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SubjectRe: [PATCH] drm: mxsfb: check framebuffer pitch
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Hi,

On 08/09/2020 10:55, Stefan Agner wrote:
> On 2020-09-07 20:18, Daniel Vetter wrote:
>> On Mon, Sep 07, 2020 at 07:17:12PM +0300, Laurent Pinchart wrote:
>>> Hi Stefan,
>>>
>>> Thank you for the patch.
>>>
>>> On Mon, Sep 07, 2020 at 06:03:43PM +0200, Stefan Agner wrote:
>>>> The lcdif IP does not support a framebuffer pitch (stride) other than
>>>> the CRTC width. Check for equality and reject the state otherwise.
>>>>
>>>> This prevents a distorted picture when using 640x800 and running the
>>>> Mesa graphics stack. Mesa tires to use a cache aligned stride, which
>>>
>>> s/tires/tries/
>>>
>>>> leads at that particular resolution to width != stride. Currently
>>>> Mesa has no fallback behavior, but rejecting this configuration allows
>>>> userspace to handle the issue correctly.
>>>
>>> I'm increasingly impressed by how featureful this IP core is :-)
>>>
>>>> Signed-off-by: Stefan Agner <stefan@agner.ch>
>>>> ---
>>>> drivers/gpu/drm/mxsfb/mxsfb_kms.c | 22 ++++++++++++++++++----
>>>> 1 file changed, 18 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/mxsfb/mxsfb_kms.c b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
>>>> index b721b8b262ce..79aa14027f91 100644
>>>> --- a/drivers/gpu/drm/mxsfb/mxsfb_kms.c
>>>> +++ b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
>>>> @@ -403,14 +403,28 @@ static int mxsfb_plane_atomic_check(struct drm_plane *plane,
>>>> {
>>>> struct mxsfb_drm_private *mxsfb = to_mxsfb_drm_private(plane->dev);
>>>> struct drm_crtc_state *crtc_state;
>>>> + unsigned int pitch;
>>>> + int ret;
>>>>
>>>> crtc_state = drm_atomic_get_new_crtc_state(plane_state->state,
>>>> &mxsfb->crtc);
>>>>
>>>> - return drm_atomic_helper_check_plane_state(plane_state, crtc_state,
>>>> - DRM_PLANE_HELPER_NO_SCALING,
>>>> - DRM_PLANE_HELPER_NO_SCALING,
>>>> - false, true);
>>>> + ret = drm_atomic_helper_check_plane_state(plane_state, crtc_state,
>>>> + DRM_PLANE_HELPER_NO_SCALING,
>>>> + DRM_PLANE_HELPER_NO_SCALING,
>>>> + false, true);
>>>> + if (ret || !plane_state->visible)
>>>
>>> Would it be more explict to check for !plane_state->fb ? Otherwise I'll
>>> have to verify that !fb always implies !visible :-)
>>>
>>>> + return ret;
>>>> +
>>>> + pitch = crtc_state->mode.hdisplay *
>>>> + plane_state->fb->format->cpp[0];
>>>
>>> This holds on a single line.
>>>
>>>> + if (plane_state->fb->pitches[0] != pitch) {
>>>> + dev_err(plane->dev->dev,
>>>> + "Invalid pitch: fb and crtc widths must be the same");
>>>
>>> I'd turn this into a dev_dbg(), printing error messages to the kernel
>>> log in response to user-triggered conditions is a bit too verbose and
>>> could flood the log.
>>>
>>> Wouldn't it be best to catch this issue when creating the framebuffer ?
>>
>> Yeah this should be verified at addfb time. We try to validate as early as
>> possible.
>> -Daniel
>>
>
> Sounds sensible. From what I can tell fb_create is the proper callback
> to implement this at addfb time. Will give this a try.
>
> FWIW, I got the idea from drivers/gpu/drm/tilcdc/tilcdc_plane.c. Maybe
> should be moved to addfb there too?

But you don't know the crtc width when creating the framebuffer.

Tomi

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