Re: [RFC PATH 1/3] drm: add support modifiers for drivers whose planes only support linear layout

[Esaki Tomohito <etom@igel.co.jp>]

Thank you for your reviews.

On 2022/01/15 1:50, Daniel Vetter wrote:
> On Wed, Dec 22, 2021 at 02:27:25PM +0900, Tomohito Esaki wrote:
>> The LINEAR modifier is advertised as default if a driver doesn't specify
>> modifiers. However, there are legacy drivers such as radeon that do not
>> support modifiers but infer the actual layout of the underlying buffer.
>> Therefore, a new flag not_support_fb_modifires is introduced for these
>> legacy drivers. Allow_fb_modifiers will be replaced with this new flag.
>>
>> Signed-off-by: Tomohito Esaki <etom@igel.co.jp>
>> ---
>>   drivers/gpu/drm/drm_plane.c   | 34 ++++++++++++++++++++++++++--------
>>   include/drm/drm_mode_config.h | 10 ++++++++++
>>   include/drm/drm_plane.h       |  3 +++
>>   3 files changed, 39 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c
>> index 82afb854141b..75308ee240c0 100644
>> --- a/drivers/gpu/drm/drm_plane.c
>> +++ b/drivers/gpu/drm/drm_plane.c
>> @@ -161,6 +161,16 @@ modifiers_ptr(struct drm_format_modifier_blob *blob)
>>   	return (struct drm_format_modifier *)(((char *)blob) + blob->modifiers_offset);
>>   }
>>   
>> +static bool check_format_modifier(struct drm_plane *plane, uint32_t format,
>> +				  uint64_t modifier)
>> +{
>> +	if (plane->funcs->format_mod_supported)
>> +		return plane->funcs->format_mod_supported(plane, format,
>> +							  modifier);
>> +
>> +	return modifier == DRM_FORMAT_MOD_LINEAR;
>> +}
>> +
>>   static int create_in_format_blob(struct drm_device *dev, struct drm_plane *plane)
>>   {
>>   	const struct drm_mode_config *config = &dev->mode_config;
>> @@ -203,16 +213,15 @@ static int create_in_format_blob(struct drm_device *dev, struct drm_plane *plane
>>   	memcpy(formats_ptr(blob_data), plane->format_types, formats_size);
>>   
>>   	/* If we can't determine support, just bail */
>> -	if (!plane->funcs->format_mod_supported)
>> +	if (config->fb_modifiers_not_supported)
>>   		goto done;
>>   
>>   	mod = modifiers_ptr(blob_data);
>>   	for (i = 0; i < plane->modifier_count; i++) {
>>   		for (j = 0; j < plane->format_count; j++) {
>> -			if (plane->funcs->format_mod_supported(plane,
>> -							       plane->format_types[j],
>> -							       plane->modifiers[i])) {
>> -
>> +			if (check_format_modifier(plane,
>> +						  plane->format_types[j],
>> +						  plane->modifiers[i])) {
>>   				mod->formats |= 1ULL << j;
>>   			}
>>   		}
>> @@ -242,6 +251,10 @@ static int __drm_universal_plane_init(struct drm_device *dev,
>>   				      const char *name, va_list ap)
>>   {
>>   	struct drm_mode_config *config = &dev->mode_config;
>> +	const uint64_t default_modifiers[] = {
>> +		DRM_FORMAT_MOD_LINEAR,
>> +		DRM_FORMAT_MOD_INVALID
>> +	};
>>   	unsigned int format_modifier_count = 0;
>>   	int ret;
>>   
>> @@ -282,6 +295,11 @@ static int __drm_universal_plane_init(struct drm_device *dev,
>>   
>>   		while (*temp_modifiers++ != DRM_FORMAT_MOD_INVALID)
>>   			format_modifier_count++;
>> +	} else {
>> +		if (!dev->mode_config.fb_modifiers_not_supported) {
>> +			format_modifiers = default_modifiers;
>> +			format_modifier_count = 1;
>> +		}
>>   	}
>>   
>>   	/* autoset the cap and check for consistency across all planes */
>> @@ -346,7 +364,7 @@ static int __drm_universal_plane_init(struct drm_device *dev,
>>   		drm_object_attach_property(&plane->base, config->prop_src_h, 0);
>>   	}
>>   
>> -	if (config->allow_fb_modifiers)
>> +	if (format_modifier_count)
>>   		create_in_format_blob(dev, plane);
>>   
>>   	return 0;
>> @@ -373,8 +391,8 @@ static int __drm_universal_plane_init(struct drm_device *dev,
>>    * drm_universal_plane_init() to let the DRM managed resource infrastructure
>>    * take care of cleanup and deallocation.
>>    *
>> - * Drivers supporting modifiers must set @format_modifiers on all their planes,
>> - * even those that only support DRM_FORMAT_MOD_LINEAR.
>> + * For drivers supporting modifiers, all planes will advertise
>> + * DRM_FORMAT_MOD_LINEAR support, if @format_modifiers is not set.
>>    *
>>    * Returns:
>>    * Zero on success, error code on failure.
>> diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h
>> index 48b7de80daf5..c56f298c55bd 100644
>> --- a/include/drm/drm_mode_config.h
>> +++ b/include/drm/drm_mode_config.h
>> @@ -920,6 +920,16 @@ struct drm_mode_config {
>>   	 */
>>   	bool allow_fb_modifiers;
>>   
>> +	/**
>> +	 * @fb_modifiers_not_supported:
>> +	 *
>> +	 * This flag is for legacy drivers such as radeon that do not support
> 
> Maybe don't put specific driver names into kerneldoc (in commit message to
> motivate your changes it's fine). It's unlikely radeon ever changes on
> this, but also no one will update this in the docs if we ever do that.
> 
> Perhaps also add that new driver should never set this, just to hammer it
> home that modifiers really should work everywhere.

I agree with you.
I'll modify this docs.

Thanks,
Tomohito Esaki

> 
> Otherwise I think this series is the right thing to do.
> -Daniel
> 
>> +	 * modifiers but infer the actual layout of the underlying buffer.
>> +	 * Generally, each drivers must support modifiers, this flag should not
>> +	 * be set.
>> +	 */
>> +	bool fb_modifiers_not_supported;
>> +
>>   	/**
>>   	 * @normalize_zpos:
>>   	 *
>> diff --git a/include/drm/drm_plane.h b/include/drm/drm_plane.h
>> index 0c1102dc4d88..cad641b1f797 100644
>> --- a/include/drm/drm_plane.h
>> +++ b/include/drm/drm_plane.h
>> @@ -803,6 +803,9 @@ void *__drmm_universal_plane_alloc(struct drm_device *dev,
>>    *
>>    * The @drm_plane_funcs.destroy hook must be NULL.
>>    *
>> + * For drivers supporting modifiers, all planes will advertise
>> + * DRM_FORMAT_MOD_LINEAR support, if @format_modifiers is not set.
>> + *
>>    * Returns:
>>    * Pointer to new plane, or ERR_PTR on failure.
>>    */
>> -- 
>> 2.17.1
>>
>