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Message-ID: <20201216210243.c6jmqlkjzk4gq2mi@intel.com>
Date: Wed, 16 Dec 2020 13:02:43 -0800
From: Ben Widawsky <ben.widawsky@...el.com>
To: Dan Williams <dan.j.williams@...el.com>
Cc: linux-cxl@...r.kernel.org,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Linux PCI <linux-pci@...r.kernel.org>,
Linux ACPI <linux-acpi@...r.kernel.org>,
Ira Weiny <ira.weiny@...el.com>,
Vishal Verma <vishal.l.verma@...el.com>,
"Kelley, Sean V" <sean.v.kelley@...el.com>,
Rafael Wysocki <rafael.j.wysocki@...el.com>,
Bjorn Helgaas <helgaas@...nel.org>,
Jonathan Cameron <Jonathan.Cameron@...wei.com>,
Jon Masters <jcm@...masters.org>,
Chris Browy <cbrowy@...ry-design.com>,
Randy Dunlap <rdunlap@...radead.org>,
Christoph Hellwig <hch@...radead.org>
Subject: Re: [RFC PATCH 12/14] cxl: Add basic debugging
On 20-12-08 19:06:46, Dan Williams wrote:
> On Tue, Dec 8, 2020 at 6:04 PM Ben Widawsky <ben.widawsky@...el.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@...el.com> wrote:
> > > >
> > > > Provide a standard debug function for use throughout the driver.
> > > >
> > > > Signed-off-by: Ben Widawsky <ben.widawsky@...el.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.
>
In that case, I'm just going to squash in the debug messages into the various
commits that need them.
> >
> > > > #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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