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    SubjectRe: [RFC PATCH 12/14] cxl: Add basic debugging
    On Tue, Dec 8, 2020 at 6:04 PM Ben Widawsky <ben.widawsky@intel.com> wrote:
    >
    > On 20-12-08 17:17:36, Dan Williams wrote:
    > > On Tue, Dec 8, 2020 at 4:24 PM Ben Widawsky <ben.widawsky@intel.com> wrote:
    > > >
    > > > Provide a standard debug function for use throughout the driver.
    > > >
    > > > Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
    > > > ---
    > > > drivers/cxl/cxl.h | 3 +++
    > > > drivers/cxl/mem.c | 26 +++++++++++++++++++++++++-
    > > > 2 files changed, 28 insertions(+), 1 deletion(-)
    > > >
    > > > diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
    > > > index 77c2dee6843c..e5afb89dab0b 100644
    > > > --- a/drivers/cxl/cxl.h
    > > > +++ b/drivers/cxl/cxl.h
    > > > @@ -9,6 +9,9 @@
    > > > #include <linux/bitops.h>
    > > > #include <linux/io.h>
    > > >
    > > > +#define cxl_debug(fmt, ...) \
    > > > + pr_debug("CXL DEBUG: %s: " fmt, __func__, ##__VA_ARGS__)
    > > > +
    > >
    > > This should be dev_dbg(), then you don't need the CXL DEBUG prefix. In
    > > fact you don't need a cxl_debug() macro at all in that case. cxl_mem
    > > might need a ->dev attribute for this purpose.
    > >
    >
    > I really like the ability to turn specific messages on and off at will. (FWIW,
    > __func__ is also redundant because pr_debug allows you to specify a flag to
    > always print the function name). While it's not very frequent events here, in
    > the future it likely will be and I think it can be really helpful to be able to
    > have that level of control.
    >
    > If you want to avoid creating a new debug functionality, I'm okay with that, but
    > I'd really like to use pr_debug instead of dev_dbg for those messages going
    > forward. Once you take that step, it seems giving contributors a macro named
    > 'cxl_debug' so they don't have to figure out when to use what, makes sense. My
    > mental separation is, dev_* is useful primarily for errors and initialization
    > debug messaging, pr_debug/trace_printk is for runtime things.
    >
    > I probably should have put that in the commit message...

    I suspect you haven't taken a look at the backed and of pr_debug() and
    dev_dbg() in a while? They both use _dynamic_func_call and enjoy all
    the benefits afforded by /sys/debug/dynamic_debug/control and the
    "dyndbg" module option for adding __func__ and enable / disable by
    line number or format message . pr_debug() and this cxl_debug() macro
    are completely superseded by dev_dbg(). Even if a driver wanted a
    common prefix on all prints there is the "#define dev_fmt ..."
    mechanism for that.

    >
    > > > #define CXL_SET_FIELD(value, field) \
    > > > ({ \
    > > > WARN_ON(!FIELD_FIT(field##_MASK, value)); \
    > > > diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c
    > > > index a2cea7ac7cc6..6b2f8d3776b5 100644
    > > > --- a/drivers/cxl/mem.c
    > > > +++ b/drivers/cxl/mem.c
    > > > @@ -122,9 +122,12 @@ static int cxl_mem_wait_for_doorbell(struct cxl_mem *cxlm)
    > > > {
    > > > const int timeout = msecs_to_jiffies(2000);
    > > > const unsigned long start = jiffies;
    > > > + unsigned long end = start;
    > > >
    > > > while (cxl_doorbell_busy(cxlm)) {
    > > > - if (time_after(jiffies, start + timeout)) {
    > > > + end = jiffies;
    > > > +
    > > > + if (time_after(end, start + timeout)) {
    > > > /* Check again in case preempted before timeout test */
    > > > if (!cxl_doorbell_busy(cxlm))
    > > > break;
    > > > @@ -133,6 +136,8 @@ static int cxl_mem_wait_for_doorbell(struct cxl_mem *cxlm)
    > > > cpu_relax();
    > > > }
    > > >
    > > > + cxl_debug("Doorbell wait took %dms",
    > > > + jiffies_to_msecs(end) - jiffies_to_msecs(start));
    > > > return 0;
    > > > }
    > > >
    > > > @@ -180,6 +185,8 @@ static int cxl_mem_mbox_send_cmd(struct cxl_mem *cxlm,
    > > > }
    > > >
    > > > /* #4 */
    > > > + cxl_debug("Sending command to %s\n",
    > > > + dev_driver_string(&cxlm->pdev->dev));
    > >
    > > dev_dbg() already includes dev_driver_string().
    > >
    > > > cxl_write_mbox_reg32(cxlm, CXLDEV_MB_CTRL_OFFSET,
    > > > CXLDEV_MB_CTRL_DOORBELL);
    > > >
    > > > @@ -308,6 +315,8 @@ static int cxl_mem_open(struct inode *inode, struct file *file)
    > > > if (!cxlmd)
    > > > return -ENXIO;
    > > >
    > > > + cxl_debug("Opened %pD\n", file);
    > > > +
    > > > file->private_data = cxlmd;
    > > >
    > > > return 0;
    > > > @@ -383,6 +392,10 @@ static int handle_mailbox_cmd_from_user(struct cxl_memdev *cxlmd,
    > > > .size_in = cmd->info.size_in,
    > > > .size_out = size_out,
    > > > };
    > > > + cxl_debug("Submitting command for user\n"
    > > > + "\topcode: %x\n"
    > > > + "\tsize: %zub/%zub\n",
    > > > + mbox_cmd.opcode, mbox_cmd.size_in, mbox_cmd.size_out);
    > > > rc = cxl_mem_mbox_send_cmd(cxlmd->cxlm, &mbox_cmd);
    > > > cxl_mem_mbox_put(cxlmd->cxlm);
    > > > if (rc)
    > > > @@ -479,6 +492,8 @@ static long cxl_mem_ioctl(struct file *file, unsigned int cmd, unsigned long arg
    > > > u32 n_commands;
    > > > int i, j;
    > > >
    > > > + cxl_debug("Query IOCTL\n");
    > > > +
    > > > if (get_user(n_commands, (u32 __user *)arg))
    > > > return -EFAULT;
    > > >
    > > > @@ -511,6 +526,8 @@ static long cxl_mem_ioctl(struct file *file, unsigned int cmd, unsigned long arg
    > > > struct cxl_mem_command c;
    > > > int rc;
    > > >
    > > > + cxl_debug("Send IOCTL\n");
    > > > +
    > > > rc = cxl_validate_cmd_from_user(u, &c);
    > > > if (rc)
    > > > return rc;
    > > > @@ -843,6 +860,13 @@ static int cxl_mem_identify(struct cxl_mem *cxlm)
    > > >
    > > > id = (struct cxl_mbox_identify *)mbox_cmd.payload;
    > > >
    > > > + cxl_debug("Driver identify command\n"
    > > > + "\tFirmware Version: %s\n"
    > > > + "\tTotal Capacity: %llu (%llu persistent)\n"
    > > > + "\tLSA size: %u\n",
    > > > + id->fw_revision, id->total_capacity, id->persistent_capacity,
    > > > + id->lsa_size);
    > > > +
    > >
    > > Seems not necessary for details that are published in sysfs?
    >
    > I was thinking for cases where driver doesn't bind, seeing the identify
    > information could be useful. This is one case where dev_dbg would also serve
    > IMO.

    There's very little that can cause bind failures after
    cxl_mem_identify() succeeds. The bind failures themselves will
    dev_err() the reason.

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