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Date:   Mon, 12 Sep 2022 14:05:36 +0200
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Ville Syrjälä <ville.syrjala@...ux.intel.com>
Cc:     David Airlie <airlied@...ux.ie>,
        Javier Martinez Canillas <javierm@...hat.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/plane-helper: Add a drm_plane_helper_atomic_check()
 helper

Hi

Am 12.09.22 um 13:18 schrieb Ville Syrjälä:
> On Mon, Sep 12, 2022 at 01:05:45PM +0200, Thomas Zimmermann wrote:
>> Hi
>>
>> Am 12.09.22 um 12:40 schrieb Ville Syrjälä:
>>> On Mon, Sep 12, 2022 at 12:15:22PM +0200, Javier Martinez Canillas wrote:
>>>> Provides a default plane state check handler for primary planes that are a
>>>> fullscreen scanout buffer and whose state scale and position can't change.
>>>>
>>>> There are some drivers that duplicate this logic in their helpers, such as
>>>> simpledrm and ssd130x. Factor out this common code into a plane helper and
>>>> make drivers use it.
>>>>
>>>> Suggested-by: Thomas Zimmermann <tzimmermann@...e.de>
>>>> Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>
>>>> ---
>>>>
>>>>    drivers/gpu/drm/drm_plane_helper.c | 29 +++++++++++++++++++++++++++++
>>>>    drivers/gpu/drm/solomon/ssd130x.c  | 18 +-----------------
>>>>    drivers/gpu/drm/tiny/simpledrm.c   | 25 +------------------------
>>>>    include/drm/drm_plane_helper.h     |  2 ++
>>>>    4 files changed, 33 insertions(+), 41 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/drm_plane_helper.c b/drivers/gpu/drm/drm_plane_helper.c
>>>> index c7785967f5bf..fb41eee74693 100644
>>>> --- a/drivers/gpu/drm/drm_plane_helper.c
>>>> +++ b/drivers/gpu/drm/drm_plane_helper.c
>>>> @@ -278,3 +278,32 @@ void drm_plane_helper_destroy(struct drm_plane *plane)
>>>>    	kfree(plane);
>>>>    }
>>>>    EXPORT_SYMBOL(drm_plane_helper_destroy);
>>>> +
>>>> +/**
>>>> + * drm_plane_helper_atomic_check() - Helper to check primary planes states
>>>> + * @plane: plane to check
>>>> + * @new_state: plane state to check
>>>
>>> That is not a plane state. Also should s/new_// since it's just
>>> the overall atomic state thing rather than some new or old state.
>>
>> Using only 'state' is non-intuitive and has lead to bugs where sub-state
>> was retrieved from the wrong state information. So we've been using
>> 'new_state' and 'old_state' explicitly in several places now.
> 
> There is no old or new drm_atomic_state. It contains both.

I (vaguely) remember a bug where a driver tried 
drm_atomic_get_new_plane_state() with the (old) state that's passed to 
atomic_update. It didn't return the expected results and modesetting 
gave slightly wrong results. So we began to be more precise about new 
and old. And whatever is stored in 'plane->state' is then just 'the state'.

I understand that the semantics of atomic_check are different from 
atomic_update, but it still doesn't hurt to talk of new_state IMHO.

Best regards
Thomas

> 
>>
>> Best regards
>> Thomas
>>
>>>
>>>> + *
>>>> + * Provides a default plane state check handler for primary planes whose atomic
>>>> + * state scale and position is not expected to change because the primary plane
>>>> + * is always a fullscreen scanout buffer.
>>>> + *
>>>> + * RETURNS:
>>>> + * Zero on success, or an errno code otherwise.
>>>> + */
>>>> +int drm_plane_helper_atomic_check(struct drm_plane *plane,
>>>> +				  struct drm_atomic_state *new_state)
>>>> +{
>>>> +	struct drm_plane_state *new_plane_state = drm_atomic_get_new_plane_state(new_state, plane);
>>>> +	struct drm_crtc *new_crtc = new_plane_state->crtc;
>>>> +	struct drm_crtc_state *new_crtc_state = NULL;
>>>> +
>>>> +	if (new_crtc)
>>>> +		new_crtc_state = drm_atomic_get_new_crtc_state(new_state, new_crtc);
>>>> +
>>>> +	return drm_atomic_helper_check_plane_state(new_plane_state, new_crtc_state,
>>>> +						   DRM_PLANE_NO_SCALING,
>>>> +						   DRM_PLANE_NO_SCALING,
>>>> +						   false, false);
>>>> +}
>>>> +EXPORT_SYMBOL(drm_plane_helper_atomic_check);
>>>> diff --git a/drivers/gpu/drm/solomon/ssd130x.c b/drivers/gpu/drm/solomon/ssd130x.c
>>>> index 79e8e2017c68..28cf9c87f86d 100644
>>>> --- a/drivers/gpu/drm/solomon/ssd130x.c
>>>> +++ b/drivers/gpu/drm/solomon/ssd130x.c
>>>> @@ -565,22 +565,6 @@ static int ssd130x_fb_blit_rect(struct drm_framebuffer *fb, const struct iosys_m
>>>>    	return ret;
>>>>    }
>>>>    
>>>> -static int ssd130x_primary_plane_helper_atomic_check(struct drm_plane *plane,
>>>> -						     struct drm_atomic_state *new_state)
>>>> -{
>>>> -	struct drm_plane_state *new_plane_state = drm_atomic_get_new_plane_state(new_state, plane);
>>>> -	struct drm_crtc *new_crtc = new_plane_state->crtc;
>>>> -	struct drm_crtc_state *new_crtc_state = NULL;
>>>> -
>>>> -	if (new_crtc)
>>>> -		new_crtc_state = drm_atomic_get_new_crtc_state(new_state, new_crtc);
>>>> -
>>>> -	return drm_atomic_helper_check_plane_state(new_plane_state, new_crtc_state,
>>>> -						   DRM_PLANE_NO_SCALING,
>>>> -						   DRM_PLANE_NO_SCALING,
>>>> -						   false, false);
>>>> -}
>>>> -
>>>>    static void ssd130x_primary_plane_helper_atomic_update(struct drm_plane *plane,
>>>>    						       struct drm_atomic_state *old_state)
>>>>    {
>>>> @@ -623,7 +607,7 @@ static void ssd130x_primary_plane_helper_atomic_disable(struct drm_plane *plane,
>>>>    
>>>>    static const struct drm_plane_helper_funcs ssd130x_primary_plane_helper_funcs = {
>>>>    	DRM_GEM_SHADOW_PLANE_HELPER_FUNCS,
>>>> -	.atomic_check = ssd130x_primary_plane_helper_atomic_check,
>>>> +	.atomic_check = drm_plane_helper_atomic_check,
>>>>    	.atomic_update = ssd130x_primary_plane_helper_atomic_update,
>>>>    	.atomic_disable = ssd130x_primary_plane_helper_atomic_disable,
>>>>    };
>>>> diff --git a/drivers/gpu/drm/tiny/simpledrm.c b/drivers/gpu/drm/tiny/simpledrm.c
>>>> index 777ccd250871..ea5b3239a659 100644
>>>> --- a/drivers/gpu/drm/tiny/simpledrm.c
>>>> +++ b/drivers/gpu/drm/tiny/simpledrm.c
>>>> @@ -469,29 +469,6 @@ static const uint64_t simpledrm_primary_plane_format_modifiers[] = {
>>>>    	DRM_FORMAT_MOD_INVALID
>>>>    };
>>>>    
>>>> -static int simpledrm_primary_plane_helper_atomic_check(struct drm_plane *plane,
>>>> -						       struct drm_atomic_state *new_state)
>>>> -{
>>>> -	struct drm_plane_state *new_plane_state = drm_atomic_get_new_plane_state(new_state, plane);
>>>> -	struct drm_crtc *new_crtc = new_plane_state->crtc;
>>>> -	struct drm_crtc_state *new_crtc_state = NULL;
>>>> -	int ret;
>>>> -
>>>> -	if (new_crtc)
>>>> -		new_crtc_state = drm_atomic_get_new_crtc_state(new_state, new_crtc);
>>>> -
>>>> -	ret = drm_atomic_helper_check_plane_state(new_plane_state, new_crtc_state,
>>>> -						  DRM_PLANE_NO_SCALING,
>>>> -						  DRM_PLANE_NO_SCALING,
>>>> -						  false, false);
>>>> -	if (ret)
>>>> -		return ret;
>>>> -	else if (!new_plane_state->visible)
>>>> -		return 0;
>>>> -
>>>> -	return 0;
>>>> -}
>>>> -
>>>>    static void simpledrm_primary_plane_helper_atomic_update(struct drm_plane *plane,
>>>>    							 struct drm_atomic_state *old_state)
>>>>    {
>>>> @@ -543,7 +520,7 @@ static void simpledrm_primary_plane_helper_atomic_disable(struct drm_plane *plan
>>>>    
>>>>    static const struct drm_plane_helper_funcs simpledrm_primary_plane_helper_funcs = {
>>>>    	DRM_GEM_SHADOW_PLANE_HELPER_FUNCS,
>>>> -	.atomic_check = simpledrm_primary_plane_helper_atomic_check,
>>>> +	.atomic_check = drm_plane_helper_atomic_check,
>>>>    	.atomic_update = simpledrm_primary_plane_helper_atomic_update,
>>>>    	.atomic_disable = simpledrm_primary_plane_helper_atomic_disable,
>>>>    };
>>>> diff --git a/include/drm/drm_plane_helper.h b/include/drm/drm_plane_helper.h
>>>> index 1781fab24dd6..7ba414655d69 100644
>>>> --- a/include/drm/drm_plane_helper.h
>>>> +++ b/include/drm/drm_plane_helper.h
>>>> @@ -41,5 +41,7 @@ int drm_plane_helper_update_primary(struct drm_plane *plane, struct drm_crtc *cr
>>>>    int drm_plane_helper_disable_primary(struct drm_plane *plane,
>>>>    				     struct drm_modeset_acquire_ctx *ctx);
>>>>    void drm_plane_helper_destroy(struct drm_plane *plane);
>>>> +int drm_plane_helper_atomic_check(struct drm_plane *plane,
>>>> +				  struct drm_atomic_state *new_state);
>>>>    
>>>>    #endif
>>>> -- 
>>>> 2.37.1
>>>
>>
>> -- 
>> Thomas Zimmermann
>> Graphics Driver Developer
>> SUSE Software Solutions Germany GmbH
>> Maxfeldstr. 5, 90409 Nürnberg, Germany
>> (HRB 36809, AG Nürnberg)
>> Geschäftsführer: Ivo Totev
> 
> 
> 
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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