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Date:   Thu, 5 Apr 2018 11:00:15 +0200
From:   Thomas Hellstrom <thellstrom@...are.com>
To:     Deepak Rawat <drawat@...are.com>, dri-devel@...ts.freedesktop.org,
        syeh@...are.com, linux-graphics-maintainer@...are.com,
        ville.syrjala@...ux.intel.com, lukasz.spintzyk@...playlink.com,
        noralf@...nnes.org, robdclark@...il.com, gustavo@...ovan.org,
        maarten.lankhorst@...ux.intel.com, seanpaul@...omium.org,
        airlied@...ux.ie, linux-kernel@...r.kernel.org
Subject: Re: [RFC 1/3] drm: Add DAMAGE_CLIPS property to plane

On 04/05/2018 09:35 AM, Daniel Vetter wrote:
> On Wed, Apr 04, 2018 at 04:49:06PM -0700, Deepak Rawat wrote:
>> From: Lukasz Spintzyk <lukasz.spintzyk@...playlink.com>
>>
>> Optional plane property to mark damaged regions on the plane in
>> framebuffer coordinates of the framebuffer attached to the plane.
>>
>> The layout of blob data is simply an array of drm_mode_rect with maximum
>> array size limited by DRM_MODE_FB_DIRTY_MAX_CLIPS. Unlike plane src
>> coordinates, damage clips are not in 16.16 fixed point.
>>
>> Damage clips are a hint to kernel as which area of framebuffer has
>> changed since last page-flip. This should be helpful for some drivers
>> especially for virtual devices where each framebuffer change needs to
>> be transmitted over network, usb, etc.
>>
>> Driver which are interested in enabling DAMAGE_CLIPS property for a
>> plane should enable this property using drm_plane_enable_damage_clips.
>>
>> Signed-off-by: Lukasz Spintzyk <lukasz.spintzyk@...playlink.com>
>> Signed-off-by: Deepak Rawat <drawat@...are.com>
> The property uapi section is missing, see:
>
> https://urldefense.proofpoint.com/v2/url?u=https-3A__dri.freedesktop.org_docs_drm_gpu_drm-2Dkms.html-23plane-2Dcomposition-2Dproperties&d=DwIBAg&c=uilaK90D4TOVoH58JNXRgQ&r=wnSlgOCqfpNS4d02vP68_E9q2BNMCwfD2OZ_6dCFVQQ&m=J31YNV1uz3IVRaorM-eo48msi9__sQurqRZrig2UE1s&s=vzsuquF1agbOw54HSC_18Kk2k9j83m8RusmDCtPAFWQ&e=
>
> Plane composition feels like the best place to put this. Please use that
> section to tie all the various bits together, including the helpers you're
> adding in the following patches for drivers to use.
>
> Bunch of nitpicks below, but overall I'm agreeing now with just going with
> fb coordinate damage rects.
>
> Like you say, the thing needed here now is userspace + driver actually
> implementing this. I'd also say the compat helper to map the legacy
> fb->dirty to this new atomic way of doing things should be included here
> (gives us a lot more testing for these new paths).
>
> Icing on the cake would be an igt to make sure kernel rejects invalid clip
> rects correctly.
>
>> ---
>>   drivers/gpu/drm/drm_atomic.c        | 42 +++++++++++++++++++++++++++++++++++++
>>   drivers/gpu/drm/drm_atomic_helper.c |  4 ++++
>>   drivers/gpu/drm/drm_mode_config.c   |  5 +++++
>>   drivers/gpu/drm/drm_plane.c         | 12 +++++++++++
>>   include/drm/drm_mode_config.h       | 15 +++++++++++++
>>   include/drm/drm_plane.h             | 16 ++++++++++++++
>>   include/uapi/drm/drm_mode.h         | 15 +++++++++++++
>>   7 files changed, 109 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
>> index 7d25c42..9226d24 100644
>> --- a/drivers/gpu/drm/drm_atomic.c
>> +++ b/drivers/gpu/drm/drm_atomic.c
>> @@ -669,6 +669,40 @@ static void drm_atomic_crtc_print_state(struct drm_printer *p,
>>   }
>>   
>>   /**
>> + * drm_atomic_set_damage_for_plane - sets the damage clips property to plane
>> + * @state: plane state
>> + * @blob: damage clips in framebuffer coordinates
>> + *
>> + * Returns:
>> + *
>> + * Zero on success, error code on failure.
>> + */
>> +static int drm_atomic_set_damage_for_plane(struct drm_plane_state *state,
>> +					   struct drm_property_blob *blob)
>> +{
>> +	if (blob == state->damage_clips)
>> +		return 0;
>> +
>> +	drm_property_blob_put(state->damage_clips);
>> +	state->damage_clips = NULL;
>> +
>> +	if (blob) {
>> +		uint32_t count = blob->length/sizeof(struct drm_rect);
>> +
>> +		if (count > DRM_MODE_FB_DIRTY_MAX_CLIPS)
>> +			return -EINVAL;
>> +
>> +		state->damage_clips = drm_property_blob_get(blob);
>> +		state->num_clips = count;
>> +	} else {
>> +		state->damage_clips = NULL;
>> +		state->num_clips = 0;
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +/**
>>    * drm_atomic_get_plane_state - get plane state
>>    * @state: global atomic state object
>>    * @plane: plane to get state object for
>> @@ -793,6 +827,12 @@ static int drm_atomic_plane_set_property(struct drm_plane *plane,
>>   		state->color_encoding = val;
>>   	} else if (property == plane->color_range_property) {
>>   		state->color_range = val;
>> +	} else if (property == config->prop_damage_clips) {
>> +		struct drm_property_blob *blob =
>> +			drm_property_lookup_blob(dev, val);
>> +		int ret = drm_atomic_set_damage_for_plane(state, blob);
> There's already a helper with size-checking built-in, see
> drm_atomic_replace_property_blob_from_id(). Wrt computing num_clips I'd
> just provide a little inline helper that does the
> blob->length/sizeof(drm_rect) conversion (it's just a shift, so fast).
>
>> +		drm_property_blob_put(blob);
>> +		return ret;
>>   	} else if (plane->funcs->atomic_set_property) {
>>   		return plane->funcs->atomic_set_property(plane, state,
>>   				property, val);
>> @@ -856,6 +896,8 @@ drm_atomic_plane_get_property(struct drm_plane *plane,
>>   		*val = state->color_encoding;
>>   	} else if (property == plane->color_range_property) {
>>   		*val = state->color_range;
>> +	} else if (property == config->prop_damage_clips) {
>> +		*val = (state->damage_clips) ? state->damage_clips->base.id : 0;
>>   	} else if (plane->funcs->atomic_get_property) {
>>   		return plane->funcs->atomic_get_property(plane, state, property, val);
>>   	} else {
>> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
>> index c356545..55b44e3 100644
>> --- a/drivers/gpu/drm/drm_atomic_helper.c
>> +++ b/drivers/gpu/drm/drm_atomic_helper.c
>> @@ -3506,6 +3506,8 @@ void __drm_atomic_helper_plane_duplicate_state(struct drm_plane *plane,
>>   
>>   	state->fence = NULL;
>>   	state->commit = NULL;
>> +	state->damage_clips = NULL;
>> +	state->num_clips = 0;
>>   }
>>   EXPORT_SYMBOL(__drm_atomic_helper_plane_duplicate_state);
>>   
>> @@ -3550,6 +3552,8 @@ void __drm_atomic_helper_plane_destroy_state(struct drm_plane_state *state)
>>   
>>   	if (state->commit)
>>   		drm_crtc_commit_put(state->commit);
>> +
>> +	drm_property_blob_put(state->damage_clips);
>>   }
>>   EXPORT_SYMBOL(__drm_atomic_helper_plane_destroy_state);
>>   
>> diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
>> index e5c6533..e93b127 100644
>> --- a/drivers/gpu/drm/drm_mode_config.c
>> +++ b/drivers/gpu/drm/drm_mode_config.c
>> @@ -293,6 +293,11 @@ static int drm_mode_create_standard_properties(struct drm_device *dev)
>>   		return -ENOMEM;
>>   	dev->mode_config.prop_crtc_id = prop;
>>   
>> +	prop = drm_property_create(dev, DRM_MODE_PROP_BLOB, "DAMAGE_CLIPS", 0);
> Bit a bikeshed, but since the coordinates are in fb pixels, not plane
> pixels, I'd call this "FB_DAMAGE_CLIPS".
>
>> +	if (!prop)
>> +		return -ENOMEM;
>> +	dev->mode_config.prop_damage_clips = prop;
>> +
>>   	prop = drm_property_create_bool(dev, DRM_MODE_PROP_ATOMIC,
>>   			"ACTIVE");
>>   	if (!prop)
>> diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c
>> index 6d2a6e4..071221b 100644
>> --- a/drivers/gpu/drm/drm_plane.c
>> +++ b/drivers/gpu/drm/drm_plane.c
>> @@ -1101,3 +1101,15 @@ int drm_mode_page_flip_ioctl(struct drm_device *dev,
>>   
>>   	return ret;
>>   }
>> +
>> +/**
>> + * drm_plane_enable_damage_clips - enable damage clips property
>> + * @plane: plane on which this property to enable.
>> + */
>> +void drm_plane_enable_damage_clips(struct drm_plane *plane)
>> +{
>> +	struct drm_device *dev = plane->dev;
>> +	struct drm_mode_config *config = &dev->mode_config;
>> +
>> +	drm_object_attach_property(&plane->base, config->prop_damage_clips, 0);
>> +}
>> diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h
>> index 7569f22..d8767da 100644
>> --- a/include/drm/drm_mode_config.h
>> +++ b/include/drm/drm_mode_config.h
>> @@ -628,6 +628,21 @@ struct drm_mode_config {
>>   	 */
>>   	struct drm_property *prop_crtc_id;
>>   	/**
>> +	 * @prop_damage_clips: Optional plane property to mark damaged regions
>> +	 * on the plane in framebuffer coordinates of the framebuffer attached
>> +	 * to the plane.
> Why should we make this optional? Looks like just another thing drivers
> might screw up, since we have multiple callbacks and things to set up for
> proper dirty tracking.
>
> One option I'm seeing is that if this is set, and it's an atomic driver,
> then we just directly call into the default atomic fb->dirty
> implementation. That way there's only 1 thing drivers need to do to set up
> dirty rect tracking, and they'll get all of it.
>
>> +	 *
>> +	 * The layout of blob data is simply an array of drm_mode_rect with
>> +	 * maximum array size limited by DRM_MODE_FB_DIRTY_MAX_CLIPS. Unlike
>> +	 * plane src coordinates, damage clips are not in 16.16 fixed point.
> I honestly have no idea where this limit is from. Worth keeping? I can
> easily imagine that userspace could trip over this - it's fairly high, but
> not unlimited.
>
>> +	 *
>> +	 * Damage clips are a hint to kernel as which area of framebuffer has
>> +	 * changed since last page-flip. This should be helpful
>> +	 * for some drivers especially for virtual devices where each
>> +	 * framebuffer change needs to be transmitted over network, usb, etc.
> I'd also clarify that userspace still must render the entire screen, i.e.
> make it more clear that it's really just a hint and not mandatory to only
> scan out the damaged parts.
>
>> +	 */
>> +	struct drm_property *prop_damage_clips;
>> +	/**
>>   	 * @prop_active: Default atomic CRTC property to control the active
>>   	 * state, which is the simplified implementation for DPMS in atomic
>>   	 * drivers.
>> diff --git a/include/drm/drm_plane.h b/include/drm/drm_plane.h
>> index f7bf4a4..9f24548 100644
>> --- a/include/drm/drm_plane.h
>> +++ b/include/drm/drm_plane.h
>> @@ -146,6 +146,21 @@ struct drm_plane_state {
>>   	 */
>>   	struct drm_crtc_commit *commit;
>>   
>> +	/*
>> +	 * @damage_clips
>> +	 *
>> +	 * blob property with damage as array of drm_rect in framebuffer
> &drm_rect gives you a nice hyperlink in the generated docs.
>
>> +	 * coodinates.
>> +	 */
>> +	struct drm_property_blob *damage_clips;
>> +
>> +	/*
>> +	 * @num_clips
>> +	 *
>> +	 * Number of drm_rect in @damage_clips.
>> +	 */
>> +	uint32_t num_clips;
>> +
>>   	struct drm_atomic_state *state;
>>   };
>>   
>> @@ -611,6 +626,7 @@ int drm_plane_init(struct drm_device *dev,
>>   		   const uint32_t *formats, unsigned int format_count,
>>   		   bool is_primary);
>>   void drm_plane_cleanup(struct drm_plane *plane);
>> +void drm_plane_enable_damage_clips(struct drm_plane *plane);
>>   
>>   /**
>>    * drm_plane_index - find the index of a registered plane
>> diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
>> index 50bcf42..0ad0d5b 100644
>> --- a/include/uapi/drm/drm_mode.h
>> +++ b/include/uapi/drm/drm_mode.h
>> @@ -873,6 +873,21 @@ struct drm_mode_revoke_lease {
>>   	__u32 lessee_id;
>>   };
>>   
>> +/**
>> + * struct drm_mode_rect - two dimensional rectangle drm_rect exported to
>> + * user-space.
>> + * @x1: horizontal starting coordinate (inclusive)
>> + * @y1: vertical starting coordinate (inclusive)
>> + * @x2: horizontal ending coordinate (exclusive)
>> + * @y2: vertical ending coordinate (exclusive)
>> + */
>> +struct drm_mode_rect {
>> +	__s32 x1;
>> +	__s32 y1;
>> +	__s32 x2;
>> +	__s32 y2;
> Why signed? Negative damage rects on an fb don't make sense to me. Also,
> please specify what this is exactly (to avoid confusion with the 16.16
> fixed point src rects), and maybe mention in the commit message why we're
> not using drm_clip_rect (going to proper uapi types and 32bit makes sense
> to me).

IMO, while we don't expect negative damage coordinates,
to avoid yet another drm uapi rect in the future when we actually need 
negative numbers signed is a good choice...

/Thomas


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