Re: [PATCH] drm/i915/gen9: fix error path in intel_init_workaround_bb

["Siluvery, Arun" <arun.siluvery@linux.intel.com>]

On 23/06/2015 17:01, Chris Wilson wrote:
> On Tue, Jun 23, 2015 at 06:58:42PM +0300, Imre Deak wrote:
>> On ti, 2015-06-23 at 16:44 +0100, Chris Wilson wrote:
>>> On Tue, Jun 23, 2015 at 06:18:21PM +0300, Imre Deak wrote:
>>>> On ti, 2015-06-23 at 16:13 +0100, Siluvery, Arun wrote:
>>>>> On 23/06/2015 15:36, Imre Deak wrote:
>>>>>> On ti, 2015-06-23 at 15:31 +0100, Chris Wilson wrote:
>>>>>>> On Tue, Jun 23, 2015 at 05:26:13PM +0300, Imre Deak wrote:
>>>>>>>> On the GEN!=8 error path we call kmap_atomic() which returns in atomic
>>>>>>>> context and then lrc_destroy_wa_ctx_obj() which can be called only in
>>>>>>>> process context. Fix this by preserving the correct cleanup order on
>>>>>>>> this error path.
>>>>>>>>
>>>>>>>> Also convert the WARN to DRM_ERROR the stack trace isn't really useful.
>>>>>>>>
>>>>>>>> Signed-off-by: Imre Deak <imre.deak@intel.com>
>>>>>>>> ---
>>>>>>>>    drivers/gpu/drm/i915/intel_lrc.c | 10 +++++++---
>>>>>>>>    1 file changed, 7 insertions(+), 3 deletions(-)
>>>>>>>>
>>>>>>>> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
>>>>>>>> index 1b50dd7..8bff1a2 100644
>>>>>>>> --- a/drivers/gpu/drm/i915/intel_lrc.c
>>>>>>>> +++ b/drivers/gpu/drm/i915/intel_lrc.c
>>>>>>>> @@ -1289,10 +1289,14 @@ static int intel_init_workaround_bb(struct intel_engine_cs *ring)
>>>>>>>>    		if (ret)
>>>>>>>>    			goto out;
>>>>>>>>    	} else {
>>>>>>>> -		WARN(INTEL_INFO(ring->dev)->gen >= 8,
>>>>>>>> -		     "WA batch buffer is not initialized for Gen%d\n",
>>>>>>>> -		     INTEL_INFO(ring->dev)->gen);
>>>>>>>> +		if (INTEL_INFO(ring->dev)->gen >= 8)
>>>>>>>> +			DRM_ERROR("WA batch buffer is not initialized for Gen%d\n",
>>>>>>>> +				  INTEL_INFO(ring->dev)->gen);
>>>>>>>> +
>>>>>>>
>>>>>>> Do this test upfront, then we don't have multiple error paths.
>>>>>>> http://paste.debian.net/255769
>>>>>>
>>>>>> I didn't bother moving it, I suppose GEN9 support will be added soon
>>>>>> anyway and we get a bit more test coverage on GEN9 meanwhile. But if you
>>>>>> insist I can move it.
>>>>>
>>>>> Hi Imre,
>>>>>
>>>>> I sent the following patch with the changes suggested by Chris.
>>>>> https://patchwork.kernel.org/patch/6661891/
>>>>> Since you sent it first, my patch can be ignored if your patch is updated.
>>>>
>>>> I'm fine applying your patch, but I would ask to convert the WARN to
>>>> DRM_ERROR. The stack trace doesn't add much to the error message and the
>>>> WARN is needlessly verbose now on BXT,SKL..
>>>
>>> I presumed Arun choose WARN because we are missing w/a and wanted
>>> someone to step forward and prove the fixes?
>>
>> Imo it's unnecessarily verbose, during development when loading the
>> driver I know that things are mostly ok if I can't see any such
>> backtraces. But no strong opinion, I can also change this locally.

Error message can easily get lost and also it is not an error to not 
apply these WA which is why we also continue. I thought WARN will 
probably get more attention and help in adding missing WA quickly.

regards
Arun

>
> An alternative would be to provide the stub wa_bb emission functions so
> that future wa need only start with a plain copy'n'paste.
> -Chris
>

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