[Intel-gfx] [PATCH v4 6/6] drm/i915: Add skl_check_nv12_surface for NV12

[Maarten Lankhorst]

Op 18-04-18 om 20:35 schreef Ville Syrjälä:
> On Wed, Apr 18, 2018 at 08:06:57PM +0200, Maarten Lankhorst wrote:
>> Op 18-04-18 om 17:32 schreef Ville Syrjälä:
>>> On Wed, Apr 18, 2018 at 09:38:13AM +0530, Vidya Srinivas wrote:
>>>> From: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
>>>>
>>>> We skip src trunction/adjustments for
>>>> NV12 case and handle the sizes directly.
>>>> Without this, pipe fifo underruns are seen on APL/KBL.
>>>>
>>>> v2: For NV12, making the src coordinates multiplier of 4
>>>>
>>>> v3: Moving all the src coords handling code for NV12
>>>> to skl_check_nv12_surface
>>>>
>>>> Signed-off-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
>>>> Signed-off-by: Vidya Srinivas <vidya.srinivas at intel.com>
>>>> ---
>>>>  drivers/gpu/drm/i915/intel_display.c | 39 ++++++++++++++++++++++++++++++++++++
>>>>  drivers/gpu/drm/i915/intel_sprite.c  | 15 ++++++++++----
>>>>  2 files changed, 50 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
>>>> index 925402e..b8dbaca 100644
>>>> --- a/drivers/gpu/drm/i915/intel_display.c
>>>> +++ b/drivers/gpu/drm/i915/intel_display.c
>>>> @@ -3118,6 +3118,42 @@ static int skl_check_main_surface(const struct intel_crtc_state *crtc_state,
>>>>  	return 0;
>>>>  }
>>>>  
>>>> +static int
>>>> +skl_check_nv12_surface(const struct intel_crtc_state *crtc_state,
>>>> +		       struct intel_plane_state *plane_state)
>>>> +{
>>>> +	int crtc_x2 = plane_state->base.crtc_x + plane_state->base.crtc_w;
>>>> +	int crtc_y2 = plane_state->base.crtc_y + plane_state->base.crtc_h;
>>>> +
>>>> +	if (((plane_state->base.src_x >> 16) % 4) != 0 ||
>>>> +	    ((plane_state->base.src_y >> 16) % 4) != 0 ||
>>>> +	    ((plane_state->base.src_w >> 16) % 4) != 0 ||
>>>> +	    ((plane_state->base.src_h >> 16) % 4) != 0) {
>>>> +		DRM_DEBUG_KMS("src coords must be multiple of 4 for NV12\n");
>>>> +		return -EINVAL;
>>>> +	}
>>> I don't really see why we should check these. The clipped coordinates
>>> are what matters.
>> To propagate our limits to the userspace. I think we should do it for all formats,
>> but NV12 is the first YUV format we have tests for. If we could we should do
>> something similar for the other YUV formats, but they have different requirements.
>>
>> In case of NV12 we don't have existing userspace, there will be nothing that
>> breaks if we enforce limits from the start.
> But what about sub-pixel coordinates? You're totally ignoring them here.
> We need to come up with some proper rules for this stuff.

Would we break anything if we disallow sub-pixel coordinates for i915 globally? It's not like we supported them before,
but I'm not sure that change would break anything.

>>>> +
>>>> +	/* Clipping would cause a 1-3 pixel gap at the edge of the screen? */
>>>> +	if ((crtc_x2 > crtc_state->pipe_src_w && crtc_state->pipe_src_w % 4) ||
>>>> +	    (crtc_y2 > crtc_state->pipe_src_h && crtc_state->pipe_src_h % 4)) {
>>>> +		DRM_DEBUG_KMS("It's not possible to clip %u,%u to %u,%u\n",
>>>> +			      crtc_x2, crtc_y2,
>>>> +			      crtc_state->pipe_src_w, crtc_state->pipe_src_h);
>>>> +		return -EINVAL;
>>>> +	}
>>> Why should we care? The current code already plays it fast and loose
>>> and allows the dst rectangle to shrink to accomodate the hw limits.
>>> If we want to change that we should change it universally.
>> Unfortunately for the other formats we already have an existing userspace
>> (X.org) that doesn't perform any validation. We can't change it for that,
>> but we can prevent future mistakes.
> We should do it uniformly. Not per-format. That will make the code
> unmaintainable real quick.
>>>> +
>>>> +	plane_state->base.src.x1 =
>>>> +		DIV_ROUND_CLOSEST(plane_state->base.src.x1, 1 << 18) << 18;
>>>> +	plane_state->base.src.x2 =
>>>> +		DIV_ROUND_CLOSEST(plane_state->base.src.x2, 1 << 18) << 18;
>>>> +	plane_state->base.src.y1 =
>>>> +		DIV_ROUND_CLOSEST(plane_state->base.src.y1, 1 << 18) << 18;
>>>> +	plane_state->base.src.y2 =
>>>> +		DIV_ROUND_CLOSEST(plane_state->base.src.y2, 1 << 18) << 18;
>>> Since this can now increase the size of the source rectangle our
>>> scaling factor checks are no longer 100% valid. We might end up with
>>> a scaling factor that is too high.
>>>
>>> I don't really like any of these "let's make NV12 behave special"
>>> tricks. We should make the code behave the same way for all pixel
>>> formats instead of adding format specific hacks.
>> This is not nivalid because we restrict the original src coordinates to be
>> a multiple of 4, you can only clip to something smaller, not to something
>> bigger. :)
> The clipped coordinates can be whatever thanks to scaling/etc.

Yes, but it will always be smaller than the original rectangle, so rounding to 4 when
the original set of coordinates were a multiple of 4 would never go outside the original
boundary.

> Also why are we trying to make everything a multiple of four? I don't
> remember any hw restrictions like that.

Well Vidya already replied, it sucks but it's what we have to live with for now. :(