Re: [RFC v3 5/8] drm/msm: update cursors asynchronously through atomic

[Archit Taneja <architt@codeaurora.org>]

On 05/17/2017 05:05 PM, Daniel Vetter wrote:
> On Wed, May 17, 2017 at 10:56:25AM +0530, Archit Taneja wrote:
>> Hi,
>>
>> On 05/16/2017 08:14 PM, Archit Taneja wrote:
>>>
>>>
>>> On 5/13/2017 12:40 AM, Gustavo Padovan wrote:
>>>> From: Gustavo Padovan <gustavo.padovan@collabora.com>
>>>>
>>>> Add support to async updates of cursors by using the new atomic
>>>> interface for that. Basically what this commit does is do what
>>>> mdp5_update_cursor_plane_legacy() did but through atomic.
>>>
>>> Works well on DB820c (which has a APQ8096 SoC).
>>>
>>> Tested-by: Archit Taneja <architt@codeaurora.org>
>>
>> Actually, after some more thorough testing, I found one issue, mentioned below.
>>
>>>
>>>>
>>>> v3: move size checks back to drivers (Ville Syrjälä)
>>>>
>>>> v2: move fb setting to core and use new state (Eric Anholt)
>>>>
>>>> Cc: Rob Clark <robdclark@gmail.com>
>>>> Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
>>>> ---
>>>>   drivers/gpu/drm/msm/mdp/mdp5/mdp5_plane.c | 151 +++++++++++++-----------------
>>>>   1 file changed, 63 insertions(+), 88 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/msm/mdp/mdp5/mdp5_plane.c b/drivers/gpu/drm/msm/mdp/mdp5/mdp5_plane.c
>>>> index a38c5fe..07106c1 100644
>>>> --- a/drivers/gpu/drm/msm/mdp/mdp5/mdp5_plane.c
>>>> +++ b/drivers/gpu/drm/msm/mdp/mdp5/mdp5_plane.c
>>>> @@ -33,15 +33,6 @@ static int mdp5_plane_mode_set(struct drm_plane *plane,
>>>>           struct drm_crtc *crtc, struct drm_framebuffer *fb,
>>>>           struct drm_rect *src, struct drm_rect *dest);
>>>>   -static int mdp5_update_cursor_plane_legacy(struct drm_plane *plane,
>>>> -        struct drm_crtc *crtc,
>>>> -        struct drm_framebuffer *fb,
>>>> -        int crtc_x, int crtc_y,
>>>> -        unsigned int crtc_w, unsigned int crtc_h,
>>>> -        uint32_t src_x, uint32_t src_y,
>>>> -        uint32_t src_w, uint32_t src_h,
>>>> -        struct drm_modeset_acquire_ctx *ctx);
>>>> -
>>>>   static struct mdp5_kms *get_kms(struct drm_plane *plane)
>>>>   {
>>>>       struct msm_drm_private *priv = plane->dev->dev_private;
>>>> @@ -257,7 +248,7 @@ static const struct drm_plane_funcs mdp5_plane_funcs = {
>>>>   };
>>>>     static const struct drm_plane_funcs mdp5_cursor_plane_funcs = {
>>>> -        .update_plane = mdp5_update_cursor_plane_legacy,
>>>> +        .update_plane = drm_atomic_helper_update_plane,
>>>>           .disable_plane = drm_atomic_helper_disable_plane,
>>>>           .destroy = mdp5_plane_destroy,
>>>>           .set_property = drm_atomic_helper_plane_set_property,
>>>> @@ -484,11 +475,73 @@ static void mdp5_plane_atomic_update(struct drm_plane *plane,
>>>>       }
>>>>   }
>>>>   +static int mdp5_plane_atomic_async_check(struct drm_plane *plane,
>>>> +                     struct drm_plane_state *state)
>>>> +{
>>>> +    struct mdp5_plane_state *mdp5_state = to_mdp5_plane_state(state);
>>>> +    struct drm_crtc_state *crtc_state;
>>>> +
>>>> +    crtc_state = drm_atomic_get_existing_crtc_state(state->state,
>>>> +                            state->crtc);
>>
>> I see a kernel splat here (a NULL pointer dereference). The async_check
>> function assumes that there is always going to be a plane_state->crtc
>> available. This doesn't seem to be the case at least in the
>> drm_atomic_helper_disable_plane() path. Moving the check to set
>> legacy_cursor_update after calling __drm_atomic_helper_disable_plane()
>> seems to fix the issue. Do you think it's a legit fix?
>
> Yes, plane_state->crtc == NULL is what happens when disabling a plane. I
> guess simplest would be to just not handle this for the async cursor
> helpers.

Okay. There is actually a check for (crtc != NULL) in drm_atomic_async_check().
The problem with it is that it is referring to the old plane state
(i.e plane->state->crtc) instead of the new plane state (i.e, plane_state->crtc).
Changing this fixes the issue without the need to touch
drm_atomic_helper_disable_plane().

>
> I thought we've had tons of igts to test this ...
>
>> One more point w.r.t msm driver is that we don't use the default
>> drm_atomic_helper_commit() for our atomic_commit op. So I had to
>> call drm_atomic_helper_async_commit() from our atomic_commit
>> implementation
>> (i.e, in msm_atomic_commit in drivers/gpu/drm/msm/msm_atomic.c)
>
> Would be great to fix that - msm predates the nonblocking support in the
> commit helper, but since this is fixed there's no reason anymore for
> driver-private commit functions. Or at least there shouldn't be, for
> almost all drivers. You can stuff all your hw commit logic into
> atomic_commit_tail.

Cool. I'll try to to convert to the commit helper funcs.

Thanks,
Archit

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