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SubjectRe: [PATCH 1/2] i2c_imc: New driver for Intel's iMC, found on LGA2011 chips
On Mar 7, 2015 6:39 AM, "Guenter Roeck" <linux@roeck-us.net> wrote:
>
> On 03/06/2015 06:50 PM, Andy Lutomirski wrote:
>>
>> Sandy Bridge Xeon and Extreme chips have integrated memory
>> controllers with (rather limited) onboard SMBUS masters. This
>> driver gives access to the bus.
>>
>> There are various groups working on standardizing a way to arbitrate
>> access to the bus between the OS, SMM firmware, a BMC, hardware
>> thermal control, etc. In the mean time, running this driver is
>> unsafe except under special circumstances. Nonetheless, this driver
>> has real users.
>>
>> As a compromise, the driver will refuse to load unless
>> i2c_imc.allow_unsafe_access=Y. When safe access becomes available,
>> we can leave this option as a way for legacy users to run the
>> driver, and we'll allow the driver to load by default if safe bus
>> access is available.
>>
>> Signed-off-by: Andy Lutomirski <luto@amacapital.net>
>> ---
>
>
> Please consider running your patch through checkpatch --strict, or at least checkpatch.
> [ I won't comment on the checkpatch problems below ]
>
>
>> drivers/i2c/busses/Kconfig | 18 ++
>> drivers/i2c/busses/Makefile | 1 +
>> drivers/i2c/busses/i2c-imc.c | 583 +++++++++++++++++++++++++++++++++++++++++++
>> 3 files changed, 602 insertions(+)
>> create mode 100644 drivers/i2c/busses/i2c-imc.c
>>
>> diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
>> index ab838d9e28b6..d6b9ce164fbf 100644
>> --- a/drivers/i2c/busses/Kconfig
>> +++ b/drivers/i2c/busses/Kconfig
>> @@ -149,6 +149,24 @@ config I2C_ISMT
>> This driver can also be built as a module. If so, the module will be
>> called i2c-ismt.
>>
>> +config I2C_IMC
>> + tristate "Intel iMC (LGA 2011) SMBus Controller"
>> + depends on PCI && X86
>> + select I2C_DIMM_BUS
>> + help
>> + If you say yes to this option, support will be included for the Intel
>> + Integrated Memory Controller SMBus host controller interface. This
>> + controller is found on LGA 2011 Xeons and Core i7 Extremes.
>> +
>> + There are currently no systems on which the kernel knows that it can
>> + safely enable this driver. For now, you need to pass this driver a
>> + scary module parameter, and you should only pass that parameter if you
>> + have a special motherboard and know exactly what you are doing.
>> + Special motherboards include the Supermicro X9DRH-iF-NV.
>> +
>> + This driver can also be built as a module. If so, the module will be
>> + called i2c-imc.
>> +
>> config I2C_PIIX4
>> tristate "Intel PIIX4 and compatible (ATI/AMD/Serverworks/Broadcom/SMSC)"
>> depends on PCI
>> diff --git a/drivers/i2c/busses/Makefile b/drivers/i2c/busses/Makefile
>> index 56388f658d2f..4287c891e782 100644
>> --- a/drivers/i2c/busses/Makefile
>> +++ b/drivers/i2c/busses/Makefile
>> @@ -15,6 +15,7 @@ obj-$(CONFIG_I2C_AMD8111) += i2c-amd8111.o
>> obj-$(CONFIG_I2C_I801) += i2c-i801.o
>> obj-$(CONFIG_I2C_ISCH) += i2c-isch.o
>> obj-$(CONFIG_I2C_ISMT) += i2c-ismt.o
>> +obj-$(CONFIG_I2C_IMC) += i2c-imc.o
>> obj-$(CONFIG_I2C_NFORCE2) += i2c-nforce2.o
>> obj-$(CONFIG_I2C_NFORCE2_S4985) += i2c-nforce2-s4985.o
>> obj-$(CONFIG_I2C_PIIX4) += i2c-piix4.o
>> diff --git a/drivers/i2c/busses/i2c-imc.c b/drivers/i2c/busses/i2c-imc.c
>> new file mode 100644
>> index 000000000000..2dbf171114c6
>> --- /dev/null
>> +++ b/drivers/i2c/busses/i2c-imc.c
>> @@ -0,0 +1,583 @@
>> +/*
>> + * Copyright (c) 2013 Andrew Lutomirski <luto@amacapital.net>
>> + *
>> + * This program is free software; you can redistribute it and/or modify
>> + * it under the terms of the GNU General Public License version 2
>> + * as published by the Free Software Foundation.
>> + *
>> + * This program is distributed in the hope that it will be useful,
>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
>> + * GNU General Public License for more details.
>> + *
>> + * You should have received a copy of the GNU General Public License
>> + * along with this program; if not, write to the Free Software
>> + * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
>> + */
>> +
>> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
>> +
>> +#include <linux/module.h>
>> +#include <linux/kernel.h>
>> +#include <linux/delay.h>
>> +#include <linux/pci.h>
>> +#include <linux/i2c.h>
>> +
>> +/*
>> + * The datasheet can be found here, for example:
>> + * http://www.intel.com/content/dam/www/public/us/en/documents/datasheets/xeon-e5-1600-2600-vol-2-datasheet.pdf
>> + *
>> + * There seem to be quite a few bugs or spec errors, though:
>> + *
>> + * - A successful transaction sets WOD and RDO.
>> + *
>> + * - The docs for TSOD_POLL_EN make no sense (see imc_channel_claim).
>> + *
>> + * - Erratum BT109, which says:
>> + *
>> + * The processor may not complete SMBus (System Management Bus)
>> + * transactions targeting the TSOD (Temperature Sensor On DIMM)
>> + * when Package C-States are enabled. Due to this erratum, if the
>> + * processor transitions into a Package C-State while an SMBus
>> + * transaction with the TSOD is in process, the processor will
>> + * suspend receipt of the transaction. The transaction completes
>> + * while the processor is in a Package C-State. Upon exiting
>> + * Package C-State, the processor will attempt to resume the
>> + * SMBus transaction, detect a protocol violation, and log an
>> + * error.
>> + *
>> + * The description notwithstanding, I've seen difficult-to-reproduce
>> + * issues when the system goes completely idle (so package C-states can
>> + * be entered) while software-initiated SMBUS transactions are in
>> + * progress.
>> + */
>> +
>> +/* Register offsets (in PCI configuration space) */
>> +#define SMBSTAT(i) (0x180 + 0x10*i)
>> +#define SMBCMD(i) (0x184 + 0x10*i)
>> +#define SMBCNTL(i) (0x188 + 0x10*i)
>> +#define SMB_TSOD_POLL_RATE_CNTR(i) (0x18C + 0x10*i)
>
>
> You might want to use (i) to avoid undesirable side effects if i is an expression.
>

Will do.

>
>> +#define SMB_TSOD_POLL_RATE (0x1A8)
>> +
>> +/* SMBSTAT fields */
>> +#define SMBSTAT_RDO (1U << 31) /* Read Data Valid */
>> +#define SMBSTAT_WOD (1U << 30) /* Write Operation Done */
>> +#define SMBSTAT_SBE (1U << 29) /* SMBus Error */
>> +#define SMBSTAT_SMB_BUSY (1U << 28) /* SMBus Busy State */
>> +/* 26:24 is the last automatically polled TSOD address */
>> +#define SMBSTAT_RDATA_MASK 0xffff /* result of a read */
>> +
>> +/* SMBCMD fields */
>> +#define SMBCMD_TRIGGER (1U << 31) /* CMD Trigger */
>> +#define SMBCMD_PNTR_SEL (1U << 30) /* HW polls TSOD with pointer */
>> +#define SMBCMD_WORD_ACCESS (1U << 29) /* word (vs byte) access */
>> +#define SMBCMD_TYPE_MASK (3U << 27) /* Mask for access type */
>> +#define SMBCMD_TYPE_READ (0U << 27) /* Read */
>> +#define SMBCMD_TYPE_WRITE (1U << 27) /* Write */
>> +#define SMBCMD_TYPE_PNTR_WRITE (3U << 27) /* Write to pointer */
>> +#define SMBCMD_SA_MASK (7U << 24) /* Slave Address high bits */
>> +#define SMBCMD_SA_SHIFT 24
>> +#define SMBCMD_BA_MASK 0xff0000 /* Bus Txn address */
>> +#define SMBCMD_BA_SHIFT 16
>> +#define SMBCMD_WDATA_MASK 0xffff /* data to write */
>> +
>> +/* SMBCNTL fields */
>> +#define SMBCNTL_DTI_MASK 0xf0000000 /* Slave Address low bits */
>> +#define SMBCNTL_DTI_SHIFT 28 /* Slave Address low bits */
>> +#define SMBCNTL_CKOVRD (1U << 27) /* # Clock Override */
>> +#define SMBCNTL_DIS_WRT (1U << 26) /* Disable Write (sadly) */
>> +#define SMBCNTL_SOFT_RST (1U << 10) /* Soft Reset */
>> +#define SMBCNTL_TSOD_POLL_EN (1U << 8) /* TSOD Polling Enable */
>> +/* Bits 0-3 and 4-6 indicate TSOD presence in various slots */
>> +
>> +/* Bits that might randomly change if we race with something. */
>> +#define SMBCMD_OUR_BITS (~(u32)SMBCMD_TRIGGER)
>> +#define SMBCNTL_OUR_BITS (SMBCNTL_DTI_MASK | SMBCNTL_TSOD_POLL_EN)
>> +
>> +/* System Address Controller, PCI dev 13 fn 6, 8086.3cf5 */
>> +#define SAD_CONTROL 0xf4
>> +
>> +#define PCI_DEVICE_ID_INTEL_SBRIDGE_BR 0x3cf5 /* 13.6 */
>> +#define PCI_DEVICE_ID_INTEL_SBRIDGE_IMC_TA 0x3ca8 /* 15.0 */
>> +
>> +static atomic_t imc_raced; /* Set permanently to 1 if we screw up. */
>> +
>> +static bool allow_unsafe_access;
>> +
>> +struct imc_channel {
>> + struct i2c_adapter adapter;
>> + struct mutex mutex;
>> + bool can_write, suspended;
>> + bool prev_tsod_poll;
>> +};
>> +
>> +struct imc_priv {
>> + struct pci_dev *pci_dev;
>> + struct imc_channel channels[2];
>> +};
>> +
>> +static int imc_wait_not_busy(struct imc_priv *priv, int chan, u32 *stat)
>> +{
>> + /*
>> + * The clock is around 100kHz, and transactions are nine cycles
>> + * per byte plus a few start/stop cycles, plus whatever clock
>> + * streching is involved. This means that polling every 70us
>> + * or so will give decent performance.
>> + *
>> + * Ideally we would calculate a good estimate for the
>> + * transaction time and sleep, but busy-waiting is an effective
>> + * workaround for an apparent Sandy Bridge bug that causes bogus
>> + * output if the system enters a package C-state. (NB: these
>> + * states are systemwide -- we don't need be running on the
>> + * right package for this to work.)
>> + */
>> +
>> + int i;
>> + for (i = 0; i < 50; i++) {
>> + pci_read_config_dword(priv->pci_dev, SMBSTAT(chan), stat);
>> + if (!(*stat & SMBSTAT_SMB_BUSY))
>> + return 0;
>> + udelay(70);
>> + }
>
>
> 70 * 50 = 3500uS or 3.5ms is a long time. Can you use usleep_range ?
> Not sure if it would buy much, just asking.

In general, it should be much closer to 70 us. Also, at least on
Sandy Bridge, we don't want to go idle here -- there's an erratum.
Not sure about IVB/Haswell.

>
>
>> +
>> + return -ETIMEDOUT;
>> +}
>> +
>> +static void imc_channel_release(struct imc_priv *priv, int chan)
>> +{
>> + /* Return to HW control. */
>> + if (priv->channels[chan].prev_tsod_poll) {
>> + u32 cntl;
>> + pci_read_config_dword(priv->pci_dev, SMBCNTL(chan), &cntl);
>> + cntl |= SMBCNTL_TSOD_POLL_EN;
>> + pci_write_config_dword(priv->pci_dev, SMBCNTL(chan), cntl);
>> + }
>> +}
>> +
>> +static int imc_channel_claim(struct imc_priv *priv, int chan)
>> +{
>> + /*
>> + * The docs are a bit confused here. We're supposed to disable TSOD
>> + * polling, then wait for busy to be cleared, then set
>> + * SMBCNTL_TSOD_POLL_EN to zero to switch to software control. But
>> + * SMBCNTL_TSOD_POLL_EN is the only documented way to turn off polling.
>> + */
>> +
>> + u32 cntl, stat;
>> +
>> + if (priv->channels[chan].suspended)
>> + return -EIO;
>> +
>> + pci_read_config_dword(priv->pci_dev, SMBCNTL(chan), &cntl);
>> + priv->channels[chan].prev_tsod_poll = !!(cntl & SMBCNTL_TSOD_POLL_EN);
>> + cntl &= ~SMBCNTL_TSOD_POLL_EN;
>> + pci_write_config_dword(priv->pci_dev, SMBCNTL(chan), cntl);
>> +
>> + /* Sometimes the hardware won't let go. */
>> + pci_read_config_dword(priv->pci_dev, SMBCNTL(chan), &cntl);
>> + if (cntl & SMBCNTL_TSOD_POLL_EN)
>> + return -EBUSY;
>> +
>> + if (imc_wait_not_busy(priv, chan, &stat) != 0) {
>> + imc_channel_release(priv, chan);
>> + return -EBUSY;
>> + }
>> +
>> + return 0; /* The channel is ours. */
>> +}
>> +
>> +static bool imc_channel_can_claim(struct imc_priv *priv, int chan)
>> +{
>> + u32 orig_cntl, cntl;
>> +
>> + /* See if we can turn off TSOD_POLL_EN. */
>> +
>> + pci_read_config_dword(priv->pci_dev, SMBCNTL(chan), &orig_cntl);
>> + pci_write_config_dword(priv->pci_dev, SMBCNTL(chan),
>> + orig_cntl & ~SMBCNTL_TSOD_POLL_EN);
>> +
>> + pci_read_config_dword(priv->pci_dev, SMBCNTL(chan), &cntl);
>> + if (cntl & SMBCNTL_TSOD_POLL_EN)
>> + return false; /* Failed. */
>> +
>> + pci_write_config_dword(priv->pci_dev, SMBCNTL(chan), orig_cntl);
>> + return true;
>> +}
>> +
>> +/*
>> + * The iMC supports five access types. The terminology is rather
>> + * inconsistent. These are the types:
>> + *
>> + * "Write to pointer register SMBus": I2C_SMBUS_WRITE, I2C_SMBUS_BYTE
>> + *
>> + * Read byte/word: I2C_SMBUS_READ, I2C_SMBUS_{BYTE|WORD}_DATA
>> + *
>> + * Write byte/word: I2C_SMBUS_WRITE, I2C_SMBUS_{BYTE|WORD}_DATA
>> + *
>> + * The pointer write operations is AFAICT completely useless for
>> + * software control, for two reasons. First, HW periodically polls any
>> + * TSODs on the bus, so it will corrupt the pointer in between SW
>> + * transactions. More importantly, the matching "read byte"/"receive
>> + * byte" (the address-less single-byte read) is not available for SW
>> + * control. Therefore, this driver doesn't implement pointer writes
>> + *
>> + * There is no PEC support.
>> + */
>> +
>> +static u32 imc_func(struct i2c_adapter *adapter)
>> +{
>> + int chan;
>> + struct imc_channel *ch;
>> + struct imc_priv *priv = i2c_get_adapdata(adapter);
>> +
>> + chan = (adapter == &priv->channels[0].adapter ? 0 : 1);
>> + ch = &priv->channels[chan];
>> +
>> + if (ch->can_write)
>> + return I2C_FUNC_SMBUS_BYTE_DATA | I2C_FUNC_SMBUS_WORD_DATA;
>> + else
>> + return I2C_FUNC_SMBUS_READ_BYTE_DATA |
>> + I2C_FUNC_SMBUS_READ_WORD_DATA;
>> +}
>> +
>> +static s32 imc_smbus_xfer(struct i2c_adapter *adap, u16 addr,
>> + unsigned short flags, char read_write, u8 command,
>> + int size, union i2c_smbus_data *data)
>> +{
>> + int ret, chan;
>> + u32 cmd = 0, cntl, final_cmd, final_cntl, stat;
>> + struct imc_channel *ch;
>> + struct imc_priv *priv = i2c_get_adapdata(adap);
>> +
>> + if (atomic_read(&imc_raced))
>> + return -EIO; /* Minimize damage. */
>> +
>> + chan = (adap == &priv->channels[0].adapter ? 0 : 1);
>> + ch = &priv->channels[chan];
>> +
>> + if (addr > 0x7f)
>> + return -EOPNOTSUPP; /* No large address support */
>> + if (flags)
>> + return -EOPNOTSUPP; /* No PEC */
>> + if (size != I2C_SMBUS_BYTE_DATA && size != I2C_SMBUS_WORD_DATA)
>> + return -EOPNOTSUPP;
>> +
>
>
> It is quite uncommon to have those checks in the code. Usually one trusts
> the infrastructure to not request unsupported functionality.
> Is this really necessary ?

No, I can remove it.

>
>
>> + /* Encode CMD part of addresses and access size */
>> + cmd |= ((u32)addr & 0x7) << SMBCMD_SA_SHIFT;
>
>
> Double space

Fixed.

>
>
>> + cmd |= ((u32)command) << SMBCMD_BA_SHIFT;
>> + if (size == I2C_SMBUS_WORD_DATA)
>> + cmd |= SMBCMD_WORD_ACCESS;
>> +
>> + /* Encode read/write and data to write */
>> + if (read_write == I2C_SMBUS_READ) {
>> + cmd |= SMBCMD_TYPE_READ;
>> + } else {
>> + cmd |= SMBCMD_TYPE_WRITE;
>> + cmd |= (size == I2C_SMBUS_WORD_DATA
>> + ? swab16(data->word)
>> + : data->byte);
>> + }
>> +
>> + mutex_lock(&ch->mutex);
>> +
>> + ret = imc_channel_claim(priv, chan);
>> + if (ret)
>> + goto out_unlock;
>> +
>> + pci_read_config_dword(priv->pci_dev, SMBCNTL(chan), &cntl);
>> + cntl &= ~SMBCNTL_DTI_MASK;
>> + cntl |= ((u32)addr >> 3) << SMBCNTL_DTI_SHIFT;
>> + pci_write_config_dword(priv->pci_dev, SMBCNTL(chan), cntl);
>> +
>> + /*
>> + * This clears SMBCMD_PNTR_SEL. We leave it cleared so that we don't
>> + * need to think about keeping the TSOD pointer state consistent with
>> + * the hardware's expectation. This probably has some miniscule
>> + * power cost, as TSOD polls will take 9 extra cycles.
>> + */
>> + cmd |= SMBCMD_TRIGGER;
>> + pci_write_config_dword(priv->pci_dev, SMBCMD(chan), cmd);
>> +
>> + if (imc_wait_not_busy(priv, chan, &stat) != 0) {
>> + /* Timeout. TODO: Reset the controller? */
>> + ret = -EIO;
>
>
> timeout -> -ETIMEDOUT ?

OK

>
>
>> + dev_err(&priv->pci_dev->dev, "controller is wedged\n");
>
>
> If this happens, it will presumably happen all the time and the message will
> pollute the log. Is the message really necessary ?

I'd rather log something to help diagnose. Would rate-limiting it be okay?

>
>
>> + goto out_release;
>> + }
>> +
>> + /*
>> + * Be paranoid: try to detect races. This will only detect races
>> + * against BIOS, not against hardware. (I've never seen this happen.)
>> + */
>> + pci_read_config_dword(priv->pci_dev, SMBCMD(chan), &final_cmd);
>> + pci_read_config_dword(priv->pci_dev, SMBCNTL(chan), &final_cntl);
>> + if (((cmd ^ final_cmd) & SMBCMD_OUR_BITS) ||
>> + ((cntl ^ final_cntl) & SMBCNTL_OUR_BITS)) {
>> + WARN(1, "iMC SMBUS raced against firmware");
>> + dev_emerg(&priv->pci_dev->dev,
>
>
> Is a stack trace and dev_emerg really warranted here ?
>

If this happens, something's very wrong and the user should stop using
the driver. We could potentially write the wrong address, and, if we
manage to screw up thermal management, we could potentially corrupt
data for to an inappropriate refresh interval.

IOW, I want to hear about it if this happens.

>
>> + "Access to channel %d raced: cmd 0x%08X->0x%08X, cntl 0x%08X->0x%08X\n",
>> + chan, cmd, final_cmd, cntl, final_cntl);
>> + atomic_set(&imc_raced, 1);
>> + ret = -EIO;
>> + goto out_release;
>> + }
>> +
>> + if (stat & SMBSTAT_SBE) {
>> + /*
>> + * Clear the error to re-enable TSOD polling. The docs say
>> + * that, as long as SBE is set, TSOD polling won't happen.
>> + * The docs also say that writing zero to this bit (which is
>> + * the only writable bit in the whole register) will clear
>> + * the error. Empirically, writing 0 does not clear SBE, but
>> + * it's probably still good to do the write in compliance with
>> + * the spec. (TSOD polling still happens and seems to
>> + * clear SBE on its own.)
>> + */
>> + pci_write_config_dword(priv->pci_dev, SMBSTAT(chan), 0);
>> + ret = -ENXIO;
>> + goto out_release;
>> + }
>> +
>> + if (read_write == I2C_SMBUS_READ) {
>> + if (stat & SMBSTAT_RDO) {
>> + /*
>> + * The iMC SMBUS controller thinks of SMBUS
>> + * words as being big-endian (MSB first).
>> + * Linux treats them as little-endian, so we need
>> + * to swap them.
>> + *
>> + * Note: the controller will often (always?) set
>> + * WOD here. This is probably a bug.
>> + */
>> + if (size == I2C_SMBUS_WORD_DATA)
>> + data->word = swab16(stat & SMBSTAT_RDATA_MASK);
>> + else
>> + data->byte = stat & 0xFF;
>> + ret = 0;
>
>
> ret is already guaranteed to be 0 here.
>
>
>> + } else {
>> + dev_err(&priv->pci_dev->dev,
>> + "Unexpected read status 0x%08X\n", stat);
>> + ret = -EIO;
>> + }
>> + } else {
>> + if (stat & SMBSTAT_WOD) {
>> + /* Same bug (?) as in the read case. */
>> + ret = 0;
>
>
> ret is already 0, so only the else case is really needed.
>

I wanted to keep the success and failure paths in the same order in
both the read and write cases. I'll remove the unnecessary
assignment, though.

>
>> + } else {
>> + dev_err(&priv->pci_dev->dev,
>> + "Unexpected write status 0x%08X\n", stat);
>> + ret = -EIO;
>> + }
>> + }
>> +
>> +out_release:
>> + imc_channel_release(priv, chan);
>> +
>> +out_unlock:
>> + mutex_unlock(&ch->mutex);
>> +
>> + return ret;
>> +}
>> +
>> +static const struct i2c_algorithm imc_smbus_algorithm = {
>> + .smbus_xfer = imc_smbus_xfer,
>> + .functionality = imc_func,
>> +};
>> +
>> +static int imc_init_channel(struct imc_priv *priv, int i, int socket)
>> +{
>> + int err;
>> + u32 val;
>> + struct imc_channel *ch = &priv->channels[i];
>> +
>> + /*
>> + * With CLTT enabled, the hardware won't let us turn
>> + * off TSOD polling. The device is completely useless
>> + * when this happens (at least without help from Intel),
>> + * but we can at least minimize confusion.
>> + */
>> + if (!imc_channel_can_claim(priv, i)) {
>> + dev_warn(&priv->pci_dev->dev,
>> + "iMC channel %d: we cannot control the HW. Is CLTT on?\n",
>> + i);
>> + return -EBUSY;
>> + }
>> +
>> + i2c_set_adapdata(&ch->adapter, priv);
>> + ch->adapter.owner = THIS_MODULE;
>> + ch->adapter.algo = &imc_smbus_algorithm;
>> + ch->adapter.dev.parent = &priv->pci_dev->dev;
>> +
>> + pci_read_config_dword(priv->pci_dev, SMBCNTL(i), &val);
>> + ch->can_write = !(val & SMBCNTL_DIS_WRT);
>> +
>> + /*
>> + * i2c_add_addapter can call imc_smbus_xfer, so we need to be
>> + * ready immediately.
>> + */
>
>
> Seems to be a comment with no value. Every adapter needs to be ready
> by the time it registers.

It surprised me :) I'll remove it.

>
>
>> + mutex_init(&ch->mutex);
>> +
>> + snprintf(ch->adapter.name, sizeof(ch->adapter.name),
>> + "iMC socket %d channel %d", socket, i);
>> + err = i2c_add_adapter(&ch->adapter);
>> + if (err) {
>> + mutex_destroy(&ch->mutex);
>> + return err;
>> + }
>> +
>> + return 0;
>> +}
>> +
>> +static void imc_free_channel(struct imc_priv *priv, int i)
>> +{
>> + struct imc_channel *ch = &priv->channels[i];
>> +
>> + /* This can recurse into imc_smbus_xfer. */
>
>
> So ?

It needs to happen before mutex_destroy. I improved the comment.

>
>
>> + i2c_del_adapter(&ch->adapter);
>> +
>> + mutex_destroy(&ch->mutex);
>> +}
>> +
>> +static struct pci_dev *imc_get_related_device(struct pci_bus *bus, unsigned int devfn, u16 devid)
>> +{
>> + struct pci_dev *ret = pci_get_slot(bus, devfn);
>
>
> ret is a bit unusual as variable name for a pointer. dev, maybe ?
>
>
>> + if (!ret)
>> + return NULL;
>> + if (ret->vendor != PCI_VENDOR_ID_INTEL || ret->device != devid) {
>> + pci_dev_put(ret);
>> + return NULL;
>> + }
>> + return ret;
>> +}
>> +
>> +static int imc_probe(struct pci_dev *dev, const struct pci_device_id *id)
>> +{
>> + int i, err;
>> + struct imc_priv *priv;
>> + struct pci_dev *sad; /* System Address Decoder */
>> + u32 sad_control;
>> +
>> + /* Paranoia: the datasheet says this is always at 15.0 */
>> + if (dev->devfn != PCI_DEVFN(15, 0))
>> + return -ENODEV;
>> +
>> + /*
>> + * The socket number is hidden away on a different PCI device.
>> + * There's another copy at devfn 11.0 offset 0x40, and an even
>> + * less convincing copy at 5.0 0x140. The actual APICID register
>> + * is "not used ... and is still implemented in hardware because
>> + * of FUD".
>> + *
>> + * In principle we could double-check that the socket matches
>> + * the numa_node from SRAT, but this is probably not worth it.
>> + */
>> + sad = imc_get_related_device(dev->bus, PCI_DEVFN(13, 6),
>> + PCI_DEVICE_ID_INTEL_SBRIDGE_BR);
>> + if (!sad)
>> + return -ENODEV;
>> + pci_read_config_dword(sad, SAD_CONTROL, &sad_control);
>> + pci_dev_put(sad);
>> +
>> + priv = kzalloc(sizeof(*priv), GFP_KERNEL);
>
>
> devm_kzalloc() ?
>

Done.

>
>> + if (!priv)
>> + return -ENOMEM;
>> + priv->pci_dev = dev;
>> +
>> + pci_set_drvdata(dev, priv);
>> +
>> + for (i = 0; i < 2; i++) {
>> + int j;
>> + err = imc_init_channel(priv, i, sad_control & 0x7);
>> + if (err) {
>> + for (j = 0; j < i; j++)
>
>
> if (i)
> imc_free_channel(priv, 0);
>
> would be a bit simpler and accomplish the same.

I want to be ready for future hardware that might support more than
two channels.

>
>
>> + imc_free_channel(priv, j);
>> + goto exit_free;
>> + }
>> + }
>> +
>> + return 0;
>> +
>> +exit_free:
>> + kfree(priv);
>> + return err;
>> +}
>> +
>> +static void imc_remove(struct pci_dev *dev)
>> +{
>> + int i;
>> + struct imc_priv *priv = pci_get_drvdata(dev);
>> +
>> + for (i = 0; i < 2; i++)
>> + imc_free_channel(priv, i);
>> +
>> + kfree(priv);
>> +}
>> +
>> +static int imc_suspend(struct pci_dev *dev, pm_message_t mesg)
>> +{
>> + int i;
>> + struct imc_priv *priv = pci_get_drvdata(dev);
>> +
>> + /* BIOS is in charge. We should finish any pending transaction */
>> + for (i = 0; i < 2; i++) {
>> + mutex_lock(&priv->channels[i].mutex);
>> + priv->channels[i].suspended = true;
>> + mutex_unlock(&priv->channels[i].mutex);
>> + }
>> +
>> + return 0;
>> +}
>> +
>> +static int imc_resume(struct pci_dev *dev)
>> +{
>> + int i;
>> + struct imc_priv *priv = pci_get_drvdata(dev);
>> +
>> + for (i = 0; i < 2; i++) {
>> + mutex_lock(&priv->channels[i].mutex);
>> + priv->channels[i].suspended = false;
>> + mutex_unlock(&priv->channels[i].mutex);
>> + }
>> +
>> + return 0;
>> +}
>> +
>> +static DEFINE_PCI_DEVICE_TABLE(imc_ids) = {
>> + { PCI_DEVICE(PCI_VENDOR_ID_INTEL, PCI_DEVICE_ID_INTEL_SBRIDGE_IMC_TA) },
>> + { 0, }
>> +};
>> +MODULE_DEVICE_TABLE(pci, imc_ids);
>> +
>> +static struct pci_driver imc_pci_driver = {
>> + .name = "imc_smbus",
>> + .id_table = imc_ids,
>> + .probe = imc_probe,
>> + .remove = imc_remove,
>> + .suspend = imc_suspend,
>> + .resume = imc_resume,
>> +};
>> +
>> +static int __init i2c_imc_init(void)
>> +{
>> + if (!allow_unsafe_access) {
>> + pr_info("disabled because we cannot safely arbitrate with firmware and hardware\n");
>> + return -EBUSY;
>
>
> Why -EBUSY and not -ENODEV ?

No real reason. Changed.

> Also not sure if the message is really warranted.
>

Me neither. It could be helpful, and it's only dev_info. I'll remove
it, though -- it'll just be noise for the vast majority of users.

>
>> + }
>> +
>> + pr_warn("using this driver is dangerous unless your firmware is specifically designed for it; use at your own risk\n");
>
>
> Seems to me this is a bit noisy. User should already know.

I think I'm willing to mildly annoy the smallish number of legitimate
allow_unsafe_access users to help scare away all the people who like
shiny decode-dimms toys and enable this because some forum told them
to. I could be convinced otherwise, though.

One other question: from my reading of the spec, it should be possible to
augment this driver to expose a temporate sensor subdevice that shows
recent cached temperatures from HW DIMM measurements. They would be
redundant with the jc42 outputs, but it would be safe to use them even on
systems without safe SMBUS arbitration. Should I do that as a followup
later on?

--Andy


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