Re: [Intel-gfx] [PATCH v5 2/5] drm/i915: Add support for async flips in I915

[Karthik B S <karthik.b.s@intel.com>]

On 7/25/2020 4:56 AM, Paulo Zanoni wrote:
> Em seg, 2020-07-20 às 17:01 +0530, Karthik B S escreveu:
>> Set the Async Address Update Enable bit in plane ctl
>> when async flip is requested.
>>
>> v2: -Move the Async flip enablement to individual patch (Paulo)
>>
>> v3: -Rebased.
>>
>> v4: -Add separate plane hook for async flip case (Ville)
>>
>> v5: -Rebased.
>>
>> Signed-off-by: Karthik B S <karthik.b.s@intel.com>
>> Signed-off-by: Vandita Kulkarni <vandita.kulkarni@intel.com>
>> ---
>>   drivers/gpu/drm/i915/display/intel_display.c |  6 +++++
>>   drivers/gpu/drm/i915/display/intel_sprite.c  | 25 ++++++++++++++++++++
>>   drivers/gpu/drm/i915/i915_reg.h              |  1 +
>>   3 files changed, 32 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
>> index b8ff032195d9..4773f39e5924 100644
>> --- a/drivers/gpu/drm/i915/display/intel_display.c
>> +++ b/drivers/gpu/drm/i915/display/intel_display.c
>> @@ -4766,6 +4766,12 @@ u32 skl_plane_ctl(const struct intel_crtc_state *crtc_state,
>>   	const struct drm_intel_sprite_colorkey *key = &plane_state->ckey;
>>   	u32 plane_ctl;
>>   
>> +	/* During Async flip, no other updates are allowed */
> 
> My understanding is that this function is fully setting the right bits
> based on the chosen config (instead of doing read-modify-write), and
> the checks for "other updates" were done before. So the logic
> implemented here of early returning doesn't make sense.
> 

Thanks for the review.
Yes the check for other updates are done before.

So I could either do read-modify-write and return early, or,
keep the existing code flow as is, since the are checks already present.

I will keep the existing flow and remove the early return in the next 
revision.
> 
>> +	if (crtc_state->uapi.async_flip) {
>> +		plane_ctl |= PLANE_CTL_ASYNC_FLIP;
> 
> I wonder why gcc does not complain we're ORing with an unitialized
> value.

Will initialize the plane_ctl variable to zero.
> 
> 
>> +		return plane_ctl;
>> +	}
>> +
>>   	plane_ctl = PLANE_CTL_ENABLE;
> 
> It seems to be the return above means we'll never even try to enable
> the plane, we're only relying on the fact that plane_ctl is not zero
> initialize so maybe  bit 31 is already set.
> 

Since we only allow async flips on planes that are already enabled,
I assumed this would not be needed. Also, other than bit 9 (async 
address update enable), this register is double buffered and cannot be 
updated asynchronously.
> 
>>   
>>   	if (INTEL_GEN(dev_priv) < 10 && !IS_GEMINILAKE(dev_priv)) {
>> diff --git a/drivers/gpu/drm/i915/display/intel_sprite.c b/drivers/gpu/drm/i915/display/intel_sprite.c
>> index c26ca029fc0a..3747482e8fa3 100644
>> --- a/drivers/gpu/drm/i915/display/intel_sprite.c
>> +++ b/drivers/gpu/drm/i915/display/intel_sprite.c
>> @@ -603,6 +603,24 @@ icl_program_input_csc(struct intel_plane *plane,
>>   			  PLANE_INPUT_CSC_POSTOFF(pipe, plane_id, 2), 0x0);
>>   }
>>   
>> +static void
>> +skl_program_async_surface_address(struct drm_i915_private *dev_priv,
>> +				  const struct intel_plane_state *plane_state,
>> +				  enum pipe pipe, enum plane_id plane_id,
>> +				  u32 surf_addr)
>> +{
>> +	unsigned long irqflags;
>> +	u32 plane_ctl = plane_state->ctl;
>> +
>> +	spin_lock_irqsave(&dev_priv->uncore.lock, irqflags);
>> +
>> +	intel_de_write_fw(dev_priv, PLANE_CTL(pipe, plane_id), plane_ctl);
>> +	intel_de_write_fw(dev_priv, PLANE_SURF(pipe, plane_id),
>> +			  intel_plane_ggtt_offset(plane_state) + surf_addr);
>> +
>> +	spin_unlock_irqrestore(&dev_priv->uncore.lock, irqflags);
>> +}
>> +
>>   static void
>>   skl_program_plane(struct intel_plane *plane,
>>   		  const struct intel_crtc_state *crtc_state,
>> @@ -631,6 +649,13 @@ skl_program_plane(struct intel_plane *plane,
>>   	u32 keymsk, keymax;
>>   	u32 plane_ctl = plane_state->ctl;
>>   
>> +	/* During Async flip, no other updates are allowed */
>> +	if (crtc_state->uapi.async_flip) {
>> +		skl_program_async_surface_address(dev_priv, plane_state,
>> +						  pipe, plane_id, surf_addr);
>> +		return;
>> +	}
> 
> 
> I'd vote for us to keep the "don't rewrite registers that shouldn't
> change" part on its own commit, since it's just an optimization. It
> could even go at the end of the series. But perhaps this is simple
> enough and not needed.
> 
>

Will move this change to the end of the series.

Thanks,
Karthik.B.S

>> +
>>   	plane_ctl |= skl_plane_ctl_crtc(crtc_state);
>>   
>>   	if (INTEL_GEN(dev_priv) >= 10 || IS_GEMINILAKE(dev_priv))
>> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
>> index 8cee06314d5d..19aad4199874 100644
>> --- a/drivers/gpu/drm/i915/i915_reg.h
>> +++ b/drivers/gpu/drm/i915/i915_reg.h
>> @@ -6935,6 +6935,7 @@ enum {
>>   #define   PLANE_CTL_TILED_X			(1 << 10)
>>   #define   PLANE_CTL_TILED_Y			(4 << 10)
>>   #define   PLANE_CTL_TILED_YF			(5 << 10)
>> +#define   PLANE_CTL_ASYNC_FLIP			(1 << 9)
>>   #define   PLANE_CTL_FLIP_HORIZONTAL		(1 << 8)
>>   #define   PLANE_CTL_MEDIA_DECOMPRESSION_ENABLE	(1 << 4) /* TGL+ */
>>   #define   PLANE_CTL_ALPHA_MASK			(0x3 << 4) /* Pre-GLK */
> 
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