Re: [PATCH v3 2/5] drm/tegra: Restore opaque and drop alpha formats on Tegra20/30

[Dmitry Osipenko]

On 21.12.2017 01:02, Thierry Reding wrote:
> On Thu, Dec 21, 2017 at 12:05:40AM +0300, Dmitry Osipenko wrote:
>> On 20.12.2017 23:16, Thierry Reding wrote:
>>> On Wed, Dec 20, 2017 at 11:01:49PM +0300, Dmitry Osipenko wrote:
>>>> On 20.12.2017 21:01, Thierry Reding wrote:
>>>>> On Wed, Dec 20, 2017 at 06:46:11PM +0300, Dmitry Osipenko wrote:
>>>>>> Commit 7772fdaef939 ("drm/tegra: Support ARGB and ABGR formats") broke
>>>>>> DRM's MODE_ADDFB IOCTL on Tegra20/30, because IOCTL uses XRGB format if
>>>>>> requested FB depth is 24bpp. As a result, Xorg doesn't work anymore with
>>>>>> both modesetting and opentegra drivers. On older Tegra's each plane has
>>>>>> a blending configuration which should be used to enable / disable alpha
>>>>>> blending and right now the blending configs are hardcoded to disabled
>>>>>> alpha blending. In order to support alpha formats properly, planes
>>>>>> blending configuration must be adjusted, until then the alpha formats
>>>>>> are equal to non-alpha.
>>>>>>
>>>>>> Fixes: 7772fdaef939 ("drm/tegra: Support ARGB and ABGR formats")
>>>>>> Signed-off-by: Dmitry Osipenko <digetx@xxxxxxxxx>
>>>>>> ---
>>>>>>  drivers/gpu/drm/tegra/dc.c    | 29 ++++++++++++++++++-----------
>>>>>>  drivers/gpu/drm/tegra/dc.h    |  1 +
>>>>>>  drivers/gpu/drm/tegra/fb.c    | 13 -------------
>>>>>>  drivers/gpu/drm/tegra/hub.c   |  3 ++-
>>>>>>  drivers/gpu/drm/tegra/plane.c | 22 +++++++++++++++++-----
>>>>>>  drivers/gpu/drm/tegra/plane.h |  2 +-
>>>>>>  6 files changed, 39 insertions(+), 31 deletions(-)
>>>>>
>>>>> This kept bugging me, so I spent some time looking at the blending
>>>>> programming. I came up with the attached patch which seems to work
>>>>> for all scenarios and is fairly similar to your patch. It has the
>>>>> added benefit that we can keep support for more formats.
>>>>>
>>>>> Any comments?
>>>>>
>>>>> Thierry
>>>>> --- >8 ---
>>>>> From 3d2b7d1a9b8239dc6940477d8783461ac60783bc Mon Sep 17 00:00:00 2001
>>>>> From: Thierry Reding <treding@xxxxxxxxxx>
>>>>> Date: Wed, 20 Dec 2017 09:39:14 +0100
>>>>> Subject: [PATCH] drm/tegra: dc: Implement legacy blending
>>>>>
>>>>> This implements alpha blending on legacy display controllers (Tegra20,
>>>>> Tegra30 and Tegra114). While it's theoretically possible to support the
>>>>> zpos property to enable userspace to specify the Z-order of each plane
>>>>> individually, this is not currently supported and the same fixed Z-
>>>>> order as previously defined is used.
>>>>
>>>> Perhaps one variant of implementing zpos could be by making overlays 'virtual',
>>>> so each virtual overlay will be backed by the real HW plane and we could swap
>>>> the HW planes of the virtual overlays, emulating zpos.
>>>>
>>>>> Reverts commit 71835caa00e8 ("drm/tegra: fb: Force alpha formats") since
>>>>> the opaque formats are now supported.
>>>>>
>>>>> Reported-by: Dmitry Osipenko <digetx@xxxxxxxxx>
>>>>> Fixes: 7772fdaef939 ("drm/tegra: Support ARGB and ABGR formats")
>>>>> Signed-off-by: Thierry Reding <treding@xxxxxxxxxx>
>>>>> ---
>>>>>  drivers/gpu/drm/tegra/dc.c    | 74 ++++++++++++++++++++++++++++++++++---------
>>>>>  drivers/gpu/drm/tegra/dc.h    | 13 ++++++++
>>>>>  drivers/gpu/drm/tegra/fb.c    | 12 -------
>>>>>  drivers/gpu/drm/tegra/plane.c | 41 ++++++++++++++++++++++++
>>>>>  drivers/gpu/drm/tegra/plane.h |  3 ++
>>>>>  5 files changed, 116 insertions(+), 27 deletions(-)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/tegra/dc.c b/drivers/gpu/drm/tegra/dc.c
>>>>> index bc65c314e00f..07c687d7f615 100644
>>>>> --- a/drivers/gpu/drm/tegra/dc.c
>>>>> +++ b/drivers/gpu/drm/tegra/dc.c
>>>>> @@ -168,32 +168,46 @@ static inline u32 compute_initial_dda(unsigned int in)
>>>>>  	return dfixed_frac(inf);
>>>>>  }
>>>>>  
>>>>> -static void tegra_plane_setup_blending_legacy(struct tegra_plane *plane)
>>>>> +static void
>>>>> +tegra_plane_setup_blending_legacy(struct tegra_plane *plane,
>>>>> +				  const struct tegra_dc_window *window)
>>>>>  {
>>>>> +	u32 foreground = BLEND_WEIGHT1(255) | BLEND_WEIGHT0(255) |
>>>>> +			 BLEND_COLOR_KEY_NONE;
>>>>> +	u32 background = BLEND_WEIGHT1(0) | BLEND_WEIGHT0(0) |
>>>>> +			 BLEND_COLOR_KEY_NONE;
>>>>> +	u32 blendnokey = BLEND_WEIGHT1(255) | BLEND_WEIGHT0(255);
>>>>> +
>>>>> +	/* enable alpha blending if window->alpha */
>>>>> +	if (window->alpha) {
>>>>> +		background |= BLEND_CONTROL_DEPENDENT;
>>>>> +		foreground |= BLEND_CONTROL_ALPHA;
>>>>> +	}
>>>>
>>>> I think dependent weight means that window doesn't have alpha transparency. So
>>>> we should set the dependent_weight mode for opaque formats and alpha_weight for
>>>> formats with alpha channel.
>>>
>>> According to the TRM, dependent weight means that its weight will be 1 -
>>> the sum of the other overlapping windows. And it certainly seems to work
>>> that way in my tests (see below).
>>
>> Yes, and you are hardcoding the blending modes regardless of the actual plane
>> format. So even if underlying window has alpha format, it will be treated as it
>> is opaque.
> 
> Ah yes, indeed. The patch currently assumes that if the current plane
> has an alpha component, then all the others will, too. That can probably
> be done fairly easily by looking at the current atomic state and
> inspecting the pixel format for each plane on the same CRTC. Let me take
> a stab at that tomorrow.

Okay, please push patch to the public repo once it is ready and let me know.
I'll rebase cursor patch on it.

> I'm wondering if we can deal with zpos, too, if we're already going
> through the trouble of looking at all planes involved. I think we can
> simply permute the WIN_BLEND register writes depending on the Z-order
> to implement proper zpos support.
I think we will have to permute the whole window state, not only the WIN_BLEND
register.

Also I'm not sure how to make topmost window opaque and underlying windows
transparent, will have to check how blending works. Maybe it not possible at all..