Re: [PATCH 1/3] drm: Introduce scaling filter mode property

[Harry Wentland <hwentlan@amd.com>]

On 2019-10-22 8:20 a.m., Ville Syrjälä wrote:
> On Tue, Oct 22, 2019 at 03:29:44PM +0530, Shashank Sharma wrote:
>> This patch adds a scaling filter mode porperty
>> to allow:
>> - A driver/HW to showcase it's scaling filter capabilities.
>> - A userspace to pick a desired effect while scaling.
>>
>> This option will be particularly useful in the scenarios where
>> Integer mode scaling is possible, and a UI client wants to pick
>> filters like Nearest-neighbor applied for non-blurry outputs.
>>
>> There was a RFC patch series published, to discus the request to enable
>> Integer mode scaling by some of the gaming communities, which can be
>> found here:
>> https://patchwork.freedesktop.org/series/66175/
>>
>> Signed-off-by: Shashank Sharma <shashank.sharma@intel.com>
>> ---
>>  drivers/gpu/drm/drm_atomic_uapi.c |  4 ++++
>>  include/drm/drm_crtc.h            | 26 ++++++++++++++++++++++++++
>>  include/drm/drm_mode_config.h     |  6 ++++++
>>  3 files changed, 36 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/drm_atomic_uapi.c b/drivers/gpu/drm/drm_atomic_uapi.c
>> index 0d466d3b0809..883329453a86 100644
>> --- a/drivers/gpu/drm/drm_atomic_uapi.c
>> +++ b/drivers/gpu/drm/drm_atomic_uapi.c
>> @@ -435,6 +435,8 @@ static int drm_atomic_crtc_set_property(struct drm_crtc *crtc,
>>  		return ret;
>>  	} else if (property == config->prop_vrr_enabled) {
>>  		state->vrr_enabled = val;
>> +	} else if (property == config->scaling_filter_property) {
>> +		state->scaling_filter = val;
>>  	} else if (property == config->degamma_lut_property) {
>>  		ret = drm_atomic_replace_property_blob_from_id(dev,
>>  					&state->degamma_lut,
>> @@ -503,6 +505,8 @@ drm_atomic_crtc_get_property(struct drm_crtc *crtc,
>>  		*val = (state->gamma_lut) ? state->gamma_lut->base.id : 0;
>>  	else if (property == config->prop_out_fence_ptr)
>>  		*val = 0;
>> +	else if (property == config->scaling_filter_property)
>> +		*val = state->scaling_filter;
>>  	else if (crtc->funcs->atomic_get_property)
>>  		return crtc->funcs->atomic_get_property(crtc, state, property, val);
>>  	else
>> diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
>> index 5e9b15a0e8c5..94c5509474a8 100644
>> --- a/include/drm/drm_crtc.h
>> +++ b/include/drm/drm_crtc.h
>> @@ -58,6 +58,25 @@ struct device_node;
>>  struct dma_fence;
>>  struct edid;
>>  
>> +enum drm_scaling_filters {
>> +	DRM_SCALING_FILTER_DEFAULT,
>> +	DRM_SCALING_FILTER_MEDIUM,
>> +	DRM_SCALING_FILTER_BILINEAR,
>> +	DRM_SCALING_FILTER_NN,
> 
> Please use real words.
> 
>> +	DRM_SCALING_FILTER_NN_IS_ONLY,
> 
> Not a big fan of this. I'd just add the explicit nearest filter
> and leave the decision whether to use it to userspace.
> 
>> +	DRM_SCALING_FILTER_EDGE_ENHANCE,
>> +	DRM_SCALING_FILTER_INVALID,
> 
> That invalid enum value seems entirely pointless.
> 
> This set of filters is pretty arbitrary. It doesn't even cover all
> Intel hw. I would probably just leave it at "default+linear+nearest"
> initially. Exposing more vague hw specific choices needs more though,
> and I'd prefer not to spend those brain cells until a real use case
> emerges.
> 

FWIW, AMD HW allows us to specify a number of horizontal and vertical
taps for scaling. Number of taps are limited by our linebuffer size. The
default is 4 in each dimension but you could have 2 v_taps and 4 h_taps
if your're running a large horizontal resolution on some ASICs.

I'm not sure it makes sense to define filters here that aren't used. It
sounds like default and nearest neighbour would suffice for now in order
to support integer scaling.

Harry

>> +};
>> +
>> +static const struct drm_prop_enum_list drm_scaling_filter_enum_list[] = {
>> +	{ DRM_SCALING_FILTER_DEFAULT, "Default" },
>> +	{ DRM_SCALING_FILTER_MEDIUM, "Medium" },
>> +	{ DRM_SCALING_FILTER_BILINEAR, "Bilinear" },
>> +	{ DRM_SCALING_FILTER_NN, "Nearest Neighbor" },
>> +	{ DRM_SCALING_FILTER_NN_IS_ONLY, "Integer Mode Scaling" },
>> +	{ DRM_SCALING_FILTER_INVALID, "Invalid" },
>> +};
>> +
>>  static inline int64_t U642I64(uint64_t val)
>>  {
>>  	return (int64_t)*((int64_t *)&val);
>> @@ -283,6 +302,13 @@ struct drm_crtc_state {
>>  	 */
>>  	u32 target_vblank;
>>  
>> +	/**
>> +	 * @scaling_filter:
>> +	 *
>> +	 * Scaling filter mode to be applied
>> +	 */
>> +	u32 scaling_filter;
> 
> We have an enum so should use it. The documentation should probably
> point out that this applies to full crtc scaling only, not plane
> scaling.
> 
>> +
>>  	/**
>>  	 * @async_flip:
>>  	 *
>> diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h
>> index 3bcbe30339f0..efd6fd55770f 100644
>> --- a/include/drm/drm_mode_config.h
>> +++ b/include/drm/drm_mode_config.h
>> @@ -914,6 +914,12 @@ struct drm_mode_config {
>>  	 */
>>  	struct drm_property *modifiers_property;
>>  
>> +	/**
>> +	 * @scaling_filter_property: CRTC property to apply a particular filter
>> +	 * while scaling in panel fitter mode.
>> +	 */
>> +	struct drm_property *scaling_filter_property;
>> +
>>  	/* cursor size */
>>  	uint32_t cursor_width, cursor_height;
>>  
>> -- 
>> 2.17.1
> 
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