linux-kernel - Re: [PATCH] drm/meson: Fix plane atomic check when no crtc for the plane

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Date:   Wed, 4 Jan 2017 14:45:44 +0100
From:   Neil Armstrong <narmstrong@...libre.com>
To:     Ville Syrjälä <ville.syrjala@...ux.intel.com>
Cc:     airlied@...ux.ie, linux-amlogic@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH] drm/meson: Fix plane atomic check when no crtc for the
 plane

On 01/04/2017 02:27 PM, Ville Syrjälä wrote:
> On Tue, Jan 03, 2017 at 10:20:54AM +0100, Neil Armstrong wrote:
>> When no CRTC is associated with the plane, the meson_plane_atomic_check()
>> call breaks the kernel with an Oops.
>>
>> Fixes: bbbe775ec5b5 ("drm: Add support for Amlogic Meson Graphic Controller")
>> Signed-off-by: Neil Armstrong <narmstrong@...libre.com>
>> ---
>>  drivers/gpu/drm/meson/meson_plane.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/meson/meson_plane.c b/drivers/gpu/drm/meson/meson_plane.c
>> index 4942ca0..7890e30 100644
>> --- a/drivers/gpu/drm/meson/meson_plane.c
>> +++ b/drivers/gpu/drm/meson/meson_plane.c
>> @@ -51,6 +51,9 @@ static int meson_plane_atomic_check(struct drm_plane *plane,
>>  	struct drm_crtc_state *crtc_state;
>>  	struct drm_rect clip = { 0, };
>>  
>> +	if (!state->crtc)
>> +		return 0;
>> +
> 
> Since you're not going to call drm_plane_helper_check_state() you will
> fail to update plane_state->visible.

Indeed I forgot about that, but i's not necessary yet since visibility is not yet handled.

> 
> What i915 does in this case is look for state->crtc first, and if that's
> NULL it'll pick the crtc from the old state (plane->state->crtc). It
> looks a bit ugly, but maybe we should hide it in a small helper function
> that could be used by all drivers?

Yes, an helper would be helpful.

> 
>>  	crtc_state = drm_atomic_get_crtc_state(state->state, state->crtc);
>>  	if (IS_ERR(crtc_state))
>>  		return PTR_ERR(crtc_state);
>> -- 
>> 1.9.1

Thanks,
Neil