Re: [PATCH v2] drm/i915: Avoid selecting unavailable BSD2 ring

[Gabriel Feceoru <gabriel.feceoru@intel.com>]

On 23.02.2016 13:05, Tvrtko Ursulin wrote:
>
> Hi,
>
> On 23/02/16 10:52, Gabriel Feceoru wrote:
>> Return error when I915_EXEC_BSD_RING2 flag is set but BSD2 ring
>> is not available in the HW.
>
> What is the reasoning behind this? So far kernel was allowing userspace
> to select these bits and execute on the first engine. With this patch it
> would start failing potentially breaking userspace. Is it not too late
> to make such change?

I noticed some inconsistencies in igt with regards to bsd and bsd1.
For instance, if bsd2 is not available, gem_sync@basic-bsd1 is skipped, 
but it's skipped because of the 2nd check gem_has_bsd2 (see 
gem_require_ring). Surprisingly gem_has_ring() didn't complain about bsd1.

This fix will make gem_has_ring() return false.

I'm not aware about legacy/compatibility issue - if that's the case, 
please disregard this.

Regards,
Gabriel

>
> Regards,
>
> Tvrtko
>
>> v2: Reworked
>> Signed-off-by: Gabriel Feceoru <gabriel.feceoru@intel.com>
>> ---
>>   drivers/gpu/drm/i915/i915_gem_execbuffer.c | 7 +++++++
>>   1 file changed, 7 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
>> b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
>> index 8fd00d2..9fbd023 100644
>> --- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
>> +++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
>> @@ -1394,6 +1394,13 @@ eb_select_ring(struct drm_i915_private *dev_priv,
>>           return -EINVAL;
>>       }
>>
>> +    if ((user_ring_id == I915_EXEC_BSD) && !HAS_BSD2(dev_priv) &&
>> +            ((args->flags & I915_EXEC_BSD_MASK) != 0)) {
>> +        DRM_DEBUG("execbuf with bsd ring but with invalid "
>> +              "bsd dispatch flags: %d\n", (int)(args->flags));
>> +        return -EINVAL;
>> +    }
>> +
>>       if (user_ring_id == I915_EXEC_BSD && HAS_BSD2(dev_priv)) {
>>           unsigned int bsd_idx = args->flags & I915_EXEC_BSD_MASK;
>>
>>
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