[PATCH] drm/gem: Check for valid formats

[Thomas Zimmermann]

Hi

Am 05.01.23 um 16:24 schrieb Daniel Vetter:
> On Tue, Jan 03, 2023 at 02:16:30PM +0100, Thomas Zimmermann wrote:
>> Hi,
>>
>> thanks for the follow-up patch.
>>
>> Am 03.01.23 um 13:53 schrieb Maíra Canal:
>>> Currently, drm_gem_fb_create() doesn't check if the pixel format is
>>> supported, which can lead to the acceptance of invalid pixel formats
>>> e.g. the acceptance of invalid modifiers. Therefore, add a check for
>>> valid formats on drm_gem_fb_create().
>>>
>>> Moreover, note that this check is only valid for atomic drivers,
>>> because, for non-atomic drivers, checking drm_any_plane_has_format() is
>>> not possible since the format list for the primary plane is fake, and
>>> we'd therefor reject valid formats.
>>>
>>> Suggested-by: Thomas Zimmermann <tzimmermann at suse.de>
>>> Signed-off-by: Maíra Canal <mcanal at igalia.com>
>>> ---
>>>    Documentation/gpu/todo.rst                   | 7 ++-----
>>>    drivers/gpu/drm/drm_gem_framebuffer_helper.c | 9 +++++++++
>>>    2 files changed, 11 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/Documentation/gpu/todo.rst b/Documentation/gpu/todo.rst
>>> index 1f8a5ebe188e..68bdafa0284f 100644
>>> --- a/Documentation/gpu/todo.rst
>>> +++ b/Documentation/gpu/todo.rst
>>> @@ -276,11 +276,8 @@ Various hold-ups:
>>>    - Need to switch to drm_fbdev_generic_setup(), otherwise a lot of the custom fb
>>>      setup code can't be deleted.
>>> -- Many drivers wrap drm_gem_fb_create() only to check for valid formats. For
>>> -  atomic drivers we could check for valid formats by calling
>>> -  drm_plane_check_pixel_format() against all planes, and pass if any plane
>>> -  supports the format. For non-atomic that's not possible since like the format
>>> -  list for the primary plane is fake and we'd therefor reject valid formats.
>>> +- Need to switch to drm_gem_fb_create(), as now drm_gem_fb_create() checks for
>>> +  valid formats for atomic drivers.
>>>    - Many drivers subclass drm_framebuffer, we'd need a embedding compatible
>>>      version of the varios drm_gem_fb_create functions. Maybe called
>>> diff --git a/drivers/gpu/drm/drm_gem_framebuffer_helper.c b/drivers/gpu/drm/drm_gem_framebuffer_helper.c
>>> index e93533b86037..b8a615a138cd 100644
>>> --- a/drivers/gpu/drm/drm_gem_framebuffer_helper.c
>>> +++ b/drivers/gpu/drm/drm_gem_framebuffer_helper.c
>>> @@ -9,6 +9,7 @@
>>>    #include <linux/module.h>
>>>    #include <drm/drm_damage_helper.h>
>>> +#include <drm/drm_drv.h>
>>>    #include <drm/drm_fourcc.h>
>>>    #include <drm/drm_framebuffer.h>
>>>    #include <drm/drm_gem.h>
>>> @@ -164,6 +165,14 @@ int drm_gem_fb_init_with_funcs(struct drm_device *dev,
>>>    		return -EINVAL;
>>>    	}
>>> +	if (drm_drv_uses_atomic_modeset(dev) &&
>>> +	    !drm_any_plane_has_format(dev, mode_cmd->pixel_format,
>>> +				      mode_cmd->modifier[0])) {
>>
>> Because this is a generic helper, it has to handle the odd cases as well.
>> Here we cannot assume modifier[0], because there's a modifier for each pixel
>> plane in multi-plane formats. (That's a different type of plane than the
>> struct plane we're passing in.) If one combination isn't supported, the
>> helper should fail.
> 
> This was a mistake in the addfb2 design, we later rectified that all
> modifiers must match. This is because the modifier itsel can change the
> number of planes (for aux compression planes and stuff like that).
> 
> The full drm format description is the (drm_fourcc, drm_format_modifier)
> pair.

Does this mean that only modifier[0] will ever contain a valid value, OR 
that all modifiers[i] have to contain the same value?

Best regards
Thomas

> 
> This should be documented somewhere already, if not, good idea to update
> addfb docs (or make them happen in the first place).
> -Daniel
> 
>>
>> We get the number of pixel planes from the format info. So the correct
>> implementation is something like that
>>
>> if (drm_drv_uses_atomic_modeset())) {
>> 	for (i = 0; i < info->num_planes; ++i) {
>>          	if (!drm_any_plane_has_format(dev, pixel_format, \
>> 				modifier[i]) {
>> 			drm_dbg_kms(dev, "error msg");
>> 			return -EINVAL;
>> 		}
>>          }
>> }
>>
>>
>>> +		drm_dbg(dev, "Unsupported pixel format %p4cc / modifier 0x%llx\n",
>>
>> drm_dbg() is for drivers. Use drm_dbg_kms() please.
>>
>> Best regards
>> Thomas
>>
>>
>>> +			&mode_cmd->pixel_format, mode_cmd->modifier[0]);
>>> +		return -EINVAL;
>>> +	}
>>> +
>>>    	for (i = 0; i < info->num_planes; i++) {
>>>    		unsigned int width = mode_cmd->width / (i ? info->hsub : 1);
>>>    		unsigned int height = mode_cmd->height / (i ? info->vsub : 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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