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    SubjectRe: [PATCH v3] applesmc: Re-work SMC comms
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    Hi Brad,

    On 2020-11-08 02:00, Brad Campbell wrote:
    > G'day Henrik,
    >
    > I noticed you'd also loosened up the requirement for SMC_STATUS_BUSY in read_smc(). I assume
    > that causes problems on the early Macbook. This is revised on the one sent earlier.
    > If you could test this on your Air1,1 it'd be appreciated.

    No, I managed to screw up the patch; you can see that I carefully added
    the same treatment for the read argument, being unsure if the BUSY state
    would remain during the AVAILABLE data phase. I can check that again,
    but unfortunately the patch in this email shows the same problem.

    I think it may be worthwhile to rethink the behavior of wait_status()
    here. If one machine shows no change after a certain status bit change,
    then perhaps the others share that behavior, and we are waiting in vain.
    Just imagine how many years of cpu that is, combined. ;-)

    Henrik

    >
    > Commit fff2d0f701e6 ("hwmon: (applesmc) avoid overlong udelay()") introduced
    > an issue whereby communication with the SMC became unreliable with write
    > errors like :
    >
    > [ 120.378614] applesmc: send_byte(0x00, 0x0300) fail: 0x40
    > [ 120.378621] applesmc: LKSB: write data fail
    > [ 120.512782] applesmc: send_byte(0x00, 0x0300) fail: 0x40
    > [ 120.512787] applesmc: LKSB: write data fail
    >
    > The original code appeared to be timing sensitive and was not reliable with
    > the timing changes in the aforementioned commit.
    >
    > This patch re-factors the SMC communication to remove the timing
    > dependencies and restore function with the changes previously committed.
    >
    > Tested on : MacbookAir6,2 MacBookPro11,1 iMac12,2
    >
    > Fixes: fff2d0f701e6 ("hwmon: (applesmc) avoid overlong udelay()")
    > Reported-by: Andreas Kemnade <andreas@kemnade.info>
    > Tested-by: Andreas Kemnade <andreas@kemnade.info> # MacBookAir6,2
    > Acked-by: Arnd Bergmann <arnd@arndb.de>
    > Signed-off-by: Brad Campbell <brad@fnarfbargle.com>
    > Signed-off-by: Henrik Rydberg <rydberg@bitmath.org>
    >
    > ---
    > Changelog :
    > v1 : Inital attempt
    > v2 : Address logic and coding style
    > v3 : Removed some debug hangover. Added tested-by. Modifications for MacBookAir1,1
    >
    > diff --git a/drivers/hwmon/applesmc.c b/drivers/hwmon/applesmc.c
    > index a18887990f4a..3e968abb37aa 100644
    > --- a/drivers/hwmon/applesmc.c
    > +++ b/drivers/hwmon/applesmc.c
    > @@ -32,6 +32,7 @@
    > #include <linux/hwmon.h>
    > #include <linux/workqueue.h>
    > #include <linux/err.h>
    > +#include <linux/bits.h>
    >
    > /* data port used by Apple SMC */
    > #define APPLESMC_DATA_PORT 0x300
    > @@ -42,6 +43,11 @@
    >
    > #define APPLESMC_MAX_DATA_LENGTH 32
    >
    > +/* Apple SMC status bits */
    > +#define SMC_STATUS_AWAITING_DATA BIT(0) /* SMC has data waiting */
    > +#define SMC_STATUS_IB_CLOSED BIT(1) /* Will ignore any input */
    > +#define SMC_STATUS_BUSY BIT(2) /* Command in progress */
    > +
    > /* wait up to 128 ms for a status change. */
    > #define APPLESMC_MIN_WAIT 0x0010
    > #define APPLESMC_RETRY_WAIT 0x0100
    > @@ -151,65 +157,73 @@ static unsigned int key_at_index;
    > static struct workqueue_struct *applesmc_led_wq;
    >
    > /*
    > - * wait_read - Wait for a byte to appear on SMC port. Callers must
    > - * hold applesmc_lock.
    > + * Wait for specific status bits with a mask on the SMC
    > + * Used before and after writes, and before reads
    > */
    > -static int wait_read(void)
    > +
    > +static int wait_status(u8 val, u8 mask)
    > {
    > unsigned long end = jiffies + (APPLESMC_MAX_WAIT * HZ) / USEC_PER_SEC;
    > u8 status;
    > int us;
    >
    > + udelay(APPLESMC_MIN_WAIT);
    > for (us = APPLESMC_MIN_WAIT; us < APPLESMC_MAX_WAIT; us <<= 1) {
    > - usleep_range(us, us * 16);
    > status = inb(APPLESMC_CMD_PORT);
    > - /* read: wait for smc to settle */
    > - if (status & 0x01)
    > + if ((status & mask) == val)
    > return 0;
    > /* timeout: give up */
    > if (time_after(jiffies, end))
    > break;
    > + usleep_range(us, us * 16);
    > }
    > -
    > - pr_warn("wait_read() fail: 0x%02x\n", status);
    > return -EIO;
    > }
    >
    > /*
    > - * send_byte - Write to SMC port, retrying when necessary. Callers
    > + * send_byte_data - Write to SMC data port. Callers
    > * must hold applesmc_lock.
    > + * Parameter skip must be true on the last write of any
    > + * command or it'll time out.
    > */
    > -static int send_byte(u8 cmd, u16 port)
    > +
    > +static int send_byte_data(u8 cmd, u16 port, bool skip)
    > {
    > - u8 status;
    > - int us;
    > - unsigned long end = jiffies + (APPLESMC_MAX_WAIT * HZ) / USEC_PER_SEC;
    > + int ret;
    >
    > + ret = wait_status(SMC_STATUS_BUSY, SMC_STATUS_BUSY | SMC_STATUS_IB_CLOSED);
    > + if (ret)
    > + return ret;
    > outb(cmd, port);
    > - for (us = APPLESMC_MIN_WAIT; us < APPLESMC_MAX_WAIT; us <<= 1) {
    > - usleep_range(us, us * 16);
    > - status = inb(APPLESMC_CMD_PORT);
    > - /* write: wait for smc to settle */
    > - if (status & 0x02)
    > - continue;
    > - /* ready: cmd accepted, return */
    > - if (status & 0x04)
    > - return 0;
    > - /* timeout: give up */
    > - if (time_after(jiffies, end))
    > - break;
    > - /* busy: long wait and resend */
    > - udelay(APPLESMC_RETRY_WAIT);
    > - outb(cmd, port);
    > - }
    > + return wait_status(skip ? 0 : SMC_STATUS_BUSY, SMC_STATUS_BUSY);
    > +}
    >
    > - pr_warn("send_byte(0x%02x, 0x%04x) fail: 0x%02x\n", cmd, port, status);
    > - return -EIO;
    > +static int send_byte(u8 cmd, u16 port)
    > +{
    > + return send_byte_data(cmd, port, false);
    > }
    >
    > +/*
    > + * send_command - Write a command to the SMC. Callers must hold applesmc_lock.
    > + * If SMC is in undefined state, any new command write resets the state machine.
    > + */
    > +
    > static int send_command(u8 cmd)
    > {
    > - return send_byte(cmd, APPLESMC_CMD_PORT);
    > + int ret;
    > + int i;
    > +
    > + for (i = 0; i < 16; i++) {
    > + ret = wait_status(0, SMC_STATUS_IB_CLOSED);
    > + if (ret)
    > + return ret;
    > +
    > + outb(cmd, APPLESMC_CMD_PORT);
    > + ret = wait_status(SMC_STATUS_BUSY, SMC_STATUS_BUSY);
    > + if (!ret)
    > + return ret;
    > + }
    > + return -EIO;
    > }
    >
    > static int send_argument(const char *key)
    > @@ -239,7 +253,8 @@ static int read_smc(u8 cmd, const char *key, u8 *buffer, u8 len)
    > }
    >
    > for (i = 0; i < len; i++) {
    > - if (wait_read()) {
    > + if (wait_status(SMC_STATUS_AWAITING_DATA,
    > + SMC_STATUS_AWAITING_DATA | SMC_STATUS_IB_CLOSED)) {
    > pr_warn("%.4s: read data[%d] fail\n", key, i);
    > return -EIO;
    > }
    > @@ -250,7 +265,7 @@ static int read_smc(u8 cmd, const char *key, u8 *buffer, u8 len)
    > for (i = 0; i < 16; i++) {
    > udelay(APPLESMC_MIN_WAIT);
    > status = inb(APPLESMC_CMD_PORT);
    > - if (!(status & 0x01))
    > + if (!(status & SMC_STATUS_AWAITING_DATA))
    > break;
    > data = inb(APPLESMC_DATA_PORT);
    > }
    > @@ -275,7 +290,7 @@ static int write_smc(u8 cmd, const char *key, const u8 *buffer, u8 len)
    > }
    >
    > for (i = 0; i < len; i++) {
    > - if (send_byte(buffer[i], APPLESMC_DATA_PORT)) {
    > + if (send_byte_data(buffer[i], APPLESMC_DATA_PORT, i == len - 1)) {
    > pr_warn("%s: write data fail\n", key);
    > return -EIO;
    > }
    >

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