[Intel-gfx] [PATCH] drm/i915: Don't load context at driver init time on SNB

[Stéphane Marchesin]

On Fri, Aug 9, 2013 at 9:55 PM, Ben Widawsky <ben at bwidawsk.net> wrote:
> On Fri, Aug 09, 2013 at 08:32:54PM -0700, Stéphane Marchesin wrote:
>> This is a partial revert of b4ae3f22d238617ca11610b29fde16cf8c0bc6e0
>> (drm/i915: load boot context at driver init time)
>>
>> This bit breaks hardware video decode for me after resume.
>>
>> Signed-off-by: Stéphane Marchesin <marcheu at chromium.org>
>> ---
>>  drivers/gpu/drm/i915/intel_pm.c | 4 ----
>>  1 file changed, 4 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
>> index f895d15..ffa4ab2 100644
>> --- a/drivers/gpu/drm/i915/intel_pm.c
>> +++ b/drivers/gpu/drm/i915/intel_pm.c
>> @@ -4614,10 +4614,6 @@ static void gen6_init_clock_gating(struct drm_device *dev)
>>                  ILK_DPARBUNIT_CLOCK_GATE_ENABLE  |
>>                  ILK_DPFDUNIT_CLOCK_GATE_ENABLE);
>>
>> -     /* WaMbcDriverBootEnable:snb */
>> -     I915_WRITE(GEN6_MBCTL, I915_READ(GEN6_MBCTL) |
>> -                GEN6_MBCTL_ENABLE_BOOT_FETCH);
>> -
>>       g4x_disable_trickle_feed(dev);
>>
>>       /* The default value should be 0x200 according to docs, but the two
>
> I was looking at this a bit with Stéphane. One thing we both see is that
> the bit isn't sticking as it should. Clearly doing the write is having
> an effect, but something is seriously wrong. Writing the bit manually
> with IGT does make the bit stick.
>
> Stéphane, could you try to write the bit with IGT before and after
> resume, and see if it helps?

It doesn't seem to stick, and so seems to have no effect.

The confusing thing is that video decode works fine before suspend,
even though that reg is 0. And after resume, it is broken, and that
reg is still 0. So something else is going on. Maybe this reg is
write-once-ever?

Stéphane