[PATCH 1/2] drm: Add DRM_DEBUG_GEM

[PATCH 1/2] drm: Add DRM_DEBUG_GEM

[Chris Wilson]

Add a new debug value to distinguish and filter upon debug messages
emanating from GEM support code.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 include/drm/drmP.h | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/include/drm/drmP.h b/include/drm/drmP.h
index f2d68d185274..e7b58e37c583 100644
--- a/include/drm/drmP.h
+++ b/include/drm/drmP.h
@@ -107,6 +107,11 @@ struct dma_buf_attachment;
  * ATOMIC: used in the atomic code.
  *	  This is the category used by the DRM_DEBUG_ATOMIC() macro.
  *
+ * GEM: used by portions of code backing the GEM interface, both in the
+ *      core (e.g. drm_gem.c) and vendor specific code.
+ *	This is the category used by the DRM_DEBUG_GEM() macro.
+ *
+ *
  * Enabling verbose debug messages is done through the drm.debug parameter,
  * each category being enabled by a bit.
  *
@@ -114,17 +119,18 @@ struct dma_buf_attachment;
  * drm.debug=0x2 will enable DRIVER messages
  * drm.debug=0x3 will enable CORE and DRIVER messages
  * ...
- * drm.debug=0xf will enable all messages
+ * drm.debug=0xff will enable all messages
  *
  * An interesting feature is that it's possible to enable verbose logging at
  * run-time by echoing the debug value in its sysfs node:
- *   # echo 0xf > /sys/module/drm/parameters/debug
+ *   # echo 0xff > /sys/module/drm/parameters/debug
  */
 #define DRM_UT_CORE 		0x01
 #define DRM_UT_DRIVER		0x02
 #define DRM_UT_KMS		0x04
 #define DRM_UT_PRIME		0x08
 #define DRM_UT_ATOMIC		0x10
+#define DRM_UT_GEM		0x20
 
 extern __printf(2, 3)
 void drm_ut_debug_printk(const char *function_name,
@@ -254,6 +260,11 @@ void drm_err(const char *format, ...);
 		if (unlikely(drm_debug & DRM_UT_ATOMIC))		\
 			drm_ut_debug_printk(__func__, fmt, ##args);	\
 	} while (0)
+#define DRM_DEBUG_GEM(fmt, args...)					\
+	do {								\
+		if (unlikely(drm_debug & DRM_UT_GEM))			\
+			drm_ut_debug_printk(__func__, fmt, ##args);	\
+	} while (0)
 
 /*@}*/
 
-- 
2.4.6

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[PATCH 2/2] drm/i915: Soften error messages in i915_gem_object_create_from_data()

[Chris Wilson]

Since we already return -EFAULT to the user, emitting an error message
*and* WARN is overkill. If the caller is upset, they can do so, but for
the purposes of debugging we need only log the erroneous values.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc:: Alex Dai <yu.dai@intel.com>
Cc: Dave Gordon <david.s.gordon@intel.com>
Cc: Tom O'Rourke <Tom.O'Rourke@intel.com>
---
 drivers/gpu/drm/i915/i915_gem.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index c1ded76a6eb4..2039798f4403 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -5243,8 +5243,8 @@ i915_gem_object_create_from_data(struct drm_device *dev,
 
 	i915_gem_object_unpin_pages(obj);
 
-	if (WARN_ON(bytes != size)) {
-		DRM_ERROR("Incomplete copy, wrote %zu of %zu", bytes, size);
+	if (bytes != size) {
+		DRM_DEBUG_GEM("Incomplete copy, wrote %zu of %zu", bytes, size);
 		ret = -EFAULT;
 		goto fail;
 	}
-- 
2.4.6

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Re: [PATCH 2/2] drm/i915: Soften error messages in i915_gem_object_create_from_data()

[Dave Gordon]

On 28/07/15 14:27, Chris Wilson wrote:
> Since we already return -EFAULT to the user, emitting an error message
> *and* WARN is overkill. If the caller is upset, they can do so, but for
> the purposes of debugging we need only log the erroneous values.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc:: Alex Dai <yu.dai@intel.com>
> Cc: Dave Gordon <david.s.gordon@intel.com>
> Cc: Tom O'Rourke <Tom.O'Rourke@intel.com>
> ---
>   drivers/gpu/drm/i915/i915_gem.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index c1ded76a6eb4..2039798f4403 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -5243,8 +5243,8 @@ i915_gem_object_create_from_data(struct drm_device *dev,
>
>   	i915_gem_object_unpin_pages(obj);
>
> -	if (WARN_ON(bytes != size)) {
> -		DRM_ERROR("Incomplete copy, wrote %zu of %zu", bytes, size);
> +	if (bytes != size) {
> +		DRM_DEBUG_GEM("Incomplete copy, wrote %zu of %zu", bytes, size);
>   		ret = -EFAULT;
>   		goto fail;
>   	}

I agree the WARN_ON() is overkill, but I think maybe the DRM_ERROR() is 
useful. The (one current) caller will report an error, but at that level 
it's just:

         DRM_ERROR("Failed to fetch GuC firmware from %s\n", ...)

with no more detail as to whether that was due to file-not-found, 
bad-file-size, out-of-memory, failed-to-get-pages, or any of the other 
errors that might arise.

At present this code is only called once, and I think this copy failure 
"shouldn't ever happen", so it won't be filling the logfile. But 
emitting the error here for the truly unexpected case (as opposed to the 
commonplace "out-of-memory" and suchlike) helps current and future 
callers avoid doing the detailed failure analysis.

Or maybe it's a good place for your (other) new macro?

	DRM_NOTICE_ON(bytes != size,
		"Incomplete copy, wrote %zu of %zu", bytes, size);

.Dave.
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Re: [PATCH 2/2] drm/i915: Soften error messages in i915_gem_object_create_from_data()

[Chris Wilson]

On Tue, Jul 28, 2015 at 05:29:09PM +0100, Dave Gordon wrote:
> On 28/07/15 14:27, Chris Wilson wrote:
> >Since we already return -EFAULT to the user, emitting an error message
> >*and* WARN is overkill. If the caller is upset, they can do so, but for
> >the purposes of debugging we need only log the erroneous values.
> >
> >Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> >Cc:: Alex Dai <yu.dai@intel.com>
> >Cc: Dave Gordon <david.s.gordon@intel.com>
> >Cc: Tom O'Rourke <Tom.O'Rourke@intel.com>
> >---
> >  drivers/gpu/drm/i915/i915_gem.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> >diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> >index c1ded76a6eb4..2039798f4403 100644
> >--- a/drivers/gpu/drm/i915/i915_gem.c
> >+++ b/drivers/gpu/drm/i915/i915_gem.c
> >@@ -5243,8 +5243,8 @@ i915_gem_object_create_from_data(struct drm_device *dev,
> >
> >  	i915_gem_object_unpin_pages(obj);
> >
> >-	if (WARN_ON(bytes != size)) {
> >-		DRM_ERROR("Incomplete copy, wrote %zu of %zu", bytes, size);
> >+	if (bytes != size) {
> >+		DRM_DEBUG_GEM("Incomplete copy, wrote %zu of %zu", bytes, size);
> >  		ret = -EFAULT;
> >  		goto fail;
> >  	}
> 
> I agree the WARN_ON() is overkill, but I think maybe the DRM_ERROR()
> is useful. The (one current) caller will report an error, but at
> that level it's just:
> 
>         DRM_ERROR("Failed to fetch GuC firmware from %s\n", ...)
> 
> with no more detail as to whether that was due to file-not-found,
> bad-file-size, out-of-memory, failed-to-get-pages, or any of the
> other errors that might arise.
> 
> At present this code is only called once, and I think this copy
> failure "shouldn't ever happen", so it won't be filling the logfile.
> But emitting the error here for the truly unexpected case (as
> opposed to the commonplace "out-of-memory" and suchlike) helps
> current and future callers avoid doing the detailed failure
> analysis.

The message is still there though, it's just a debug message for the
developer. And all it could mean is that the caller passed in a bad
value for the size.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
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Re: [PATCH 2/2] drm/i915: Soften error messages in i915_gem_object_create_from_data()

[Dave Gordon]

On 28/07/15 17:34, Chris Wilson wrote:
> On Tue, Jul 28, 2015 at 05:29:09PM +0100, Dave Gordon wrote:
>> On 28/07/15 14:27, Chris Wilson wrote:
>>> Since we already return -EFAULT to the user, emitting an error message
>>> *and* WARN is overkill. If the caller is upset, they can do so, but for
>>> the purposes of debugging we need only log the erroneous values.
>>>
>>> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
>>> Cc:: Alex Dai <yu.dai@intel.com>
>>> Cc: Dave Gordon <david.s.gordon@intel.com>
>>> Cc: Tom O'Rourke <Tom.O'Rourke@intel.com>
>>> ---
>>>   drivers/gpu/drm/i915/i915_gem.c | 4 ++--
>>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
>>> index c1ded76a6eb4..2039798f4403 100644
>>> --- a/drivers/gpu/drm/i915/i915_gem.c
>>> +++ b/drivers/gpu/drm/i915/i915_gem.c
>>> @@ -5243,8 +5243,8 @@ i915_gem_object_create_from_data(struct drm_device *dev,
>>>
>>>   	i915_gem_object_unpin_pages(obj);
>>>
>>> -	if (WARN_ON(bytes != size)) {
>>> -		DRM_ERROR("Incomplete copy, wrote %zu of %zu", bytes, size);
>>> +	if (bytes != size) {
>>> +		DRM_DEBUG_GEM("Incomplete copy, wrote %zu of %zu", bytes, size);
>>>   		ret = -EFAULT;
>>>   		goto fail;
>>>   	}
>>
>> I agree the WARN_ON() is overkill, but I think maybe the DRM_ERROR()
>> is useful. The (one current) caller will report an error, but at
>> that level it's just:
>>
>>          DRM_ERROR("Failed to fetch GuC firmware from %s\n", ...)
>>
>> with no more detail as to whether that was due to file-not-found,
>> bad-file-size, out-of-memory, failed-to-get-pages, or any of the
>> other errors that might arise.
>>
>> At present this code is only called once, and I think this copy
>> failure "shouldn't ever happen", so it won't be filling the logfile.
>> But emitting the error here for the truly unexpected case (as
>> opposed to the commonplace "out-of-memory" and suchlike) helps
>> current and future callers avoid doing the detailed failure
>> analysis.
>
> The message is still there though, it's just a debug message for the
> developer. And all it could mean is that the caller passed in a bad
> value for the size.
> -Chris

I'm not sure you could trigger it with a bad size. The copy-target has 
just been allocated (in this function) and so is known to be the right 
size. If the size specified is larger than the data source buffer, the 
copy will likely have OOPSed anyway - or just continued with whatever 
happens to be next in memory.

So AFAICT the bytes vs. size mismatch can only happen if something is 
broken in the GEM (or SG-list) framework, hence worth announcing. If you 
reload the driver with debug enabled, it probably won't happen again 
(and you would have to reload, not just change the debug level, because 
at present this is only called during driver load).

If not an actual ERROR, then maybe a NOTICE is the right level:

     DRM_NOTICE_IF(bytes != size,
         "Incomplete copy, wrote %zu of %zu", bytes, size);

so the the support engineer who sees the "failed to fetch" message in 
the log at least gets some hint about what particular weirdness has 
occurred on this occasion. (Other cases are easier: missing firmware 
file is obvious, wrong version gets a specific ERROR in the log; and 
these errors would be persistent. But a copy-fail would be a puzzle.)

.Dave.

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Re: [PATCH 2/2] drm/i915: Soften error messages in i915_gem_object_create_from_data()

[Chris Wilson]

On Tue, Jul 28, 2015 at 06:09:16PM +0100, Dave Gordon wrote:
> On 28/07/15 17:34, Chris Wilson wrote:
> >On Tue, Jul 28, 2015 at 05:29:09PM +0100, Dave Gordon wrote:
> >>On 28/07/15 14:27, Chris Wilson wrote:
> >>>Since we already return -EFAULT to the user, emitting an error message
> >>>*and* WARN is overkill. If the caller is upset, they can do so, but for
> >>>the purposes of debugging we need only log the erroneous values.
> >>>
> >>>Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> >>>Cc:: Alex Dai <yu.dai@intel.com>
> >>>Cc: Dave Gordon <david.s.gordon@intel.com>
> >>>Cc: Tom O'Rourke <Tom.O'Rourke@intel.com>
> >>>---
> >>>  drivers/gpu/drm/i915/i915_gem.c | 4 ++--
> >>>  1 file changed, 2 insertions(+), 2 deletions(-)
> >>>
> >>>diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> >>>index c1ded76a6eb4..2039798f4403 100644
> >>>--- a/drivers/gpu/drm/i915/i915_gem.c
> >>>+++ b/drivers/gpu/drm/i915/i915_gem.c
> >>>@@ -5243,8 +5243,8 @@ i915_gem_object_create_from_data(struct drm_device *dev,
> >>>
> >>>  	i915_gem_object_unpin_pages(obj);
> >>>
> >>>-	if (WARN_ON(bytes != size)) {
> >>>-		DRM_ERROR("Incomplete copy, wrote %zu of %zu", bytes, size);
> >>>+	if (bytes != size) {
> >>>+		DRM_DEBUG_GEM("Incomplete copy, wrote %zu of %zu", bytes, size);
> >>>  		ret = -EFAULT;
> >>>  		goto fail;
> >>>  	}
> >>
> >>I agree the WARN_ON() is overkill, but I think maybe the DRM_ERROR()
> >>is useful. The (one current) caller will report an error, but at
> >>that level it's just:
> >>
> >>         DRM_ERROR("Failed to fetch GuC firmware from %s\n", ...)
> >>
> >>with no more detail as to whether that was due to file-not-found,
> >>bad-file-size, out-of-memory, failed-to-get-pages, or any of the
> >>other errors that might arise.
> >>
> >>At present this code is only called once, and I think this copy
> >>failure "shouldn't ever happen", so it won't be filling the logfile.
> >>But emitting the error here for the truly unexpected case (as
> >>opposed to the commonplace "out-of-memory" and suchlike) helps
> >>current and future callers avoid doing the detailed failure
> >>analysis.
> >
> >The message is still there though, it's just a debug message for the
> >developer. And all it could mean is that the caller passed in a bad
> >value for the size.
> >-Chris
> 
> I'm not sure you could trigger it with a bad size. The copy-target
> has just been allocated (in this function) and so is known to be the
> right size. If the size specified is larger than the data source
> buffer, the copy will likely have OOPSed anyway - or just continued
> with whatever happens to be next in memory.
> 
> So AFAICT the bytes vs. size mismatch can only happen if something
> is broken in the GEM (or SG-list) framework, hence worth announcing.
> If you reload the driver with debug enabled, it probably won't
> happen again (and you would have to reload, not just change the
> debug level, because at present this is only called during driver
> load).

Hmm, I was thinking that the access of data[size] would be checked and
the likely cause of the failure (thinking this was basically just
another copy_from_user check). I disagree that this one failure is any
more significant that any of the other internal failure cases then.

> If not an actual ERROR, then maybe a NOTICE is the right level:

No.
 
>     DRM_NOTICE_IF(bytes != size,
>         "Incomplete copy, wrote %zu of %zu", bytes, size);
> 
> so the the support engineer who sees the "failed to fetch" message
> in the log at least gets some hint about what particular weirdness
> has occurred on this occasion. (Other cases are easier: missing
> firmware file is obvious, wrong version gets a specific ERROR in the
> log; and these errors would be persistent. But a copy-fail would be
> a puzzle.)

That equally applies to a debug message. And even more so since EFAULT
here is unique. Under my assumption bytes would be recognisable in the
context of the caller, however if it ever happens it will be an equally
opaque value.

Given your arguments here, I think we should just remove it.
-Chris

-- 
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