Re: [PATCH v4 03/25] drm/gem-dma: Compute dumb-buffer sizes with drm_mode_size_dumb()

[Thomas Zimmermann <tzimmermann@suse.de>]

Hi

Am 12.06.25 um 10:43 schrieb Tomi Valkeinen:
> Hi,
>
> On 11/03/2025 17:47, Thomas Zimmermann wrote:
>> Call drm_mode_size_dumb() to compute dumb-buffer scanline pitch and
>> buffer size. Align the pitch to a multiple of 8.
>>
>> Push the current calculation into the only direct caller imx. Imx's
>> hardware requires the framebuffer width to be aligned to 8. The
>> driver's current approach is actually incorrect, as it only guarantees
>> this implicitly and requires bpp to be a multiple of 8 already. A
>> later commit will fix this problem by aligning the scanline pitch
>> such that an aligned width still fits into each scanline's memory.
>>
>> A number of other drivers are build on top of gem-dma helpers and
>> implement their own dumb-buffer allocation. These drivers invoke
>> drm_gem_dma_dumb_create_internal(), which is not affected by this
>> commit.
>>
>> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
>> ---
>>   drivers/gpu/drm/drm_gem_dma_helper.c     | 7 +++++--
>>   drivers/gpu/drm/imx/ipuv3/imx-drm-core.c | 2 ++
>>   2 files changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_gem_dma_helper.c b/drivers/gpu/drm/drm_gem_dma_helper.c
>> index b7f033d4352a..49be9b033610 100644
>> --- a/drivers/gpu/drm/drm_gem_dma_helper.c
>> +++ b/drivers/gpu/drm/drm_gem_dma_helper.c
>> @@ -20,6 +20,7 @@
>>   #include <drm/drm.h>
>>   #include <drm/drm_device.h>
>>   #include <drm/drm_drv.h>
>> +#include <drm/drm_dumb_buffers.h>
>>   #include <drm/drm_gem_dma_helper.h>
>>   #include <drm/drm_vma_manager.h>
>>   
>> @@ -304,9 +305,11 @@ int drm_gem_dma_dumb_create(struct drm_file *file_priv,
>>   			    struct drm_mode_create_dumb *args)
>>   {
>>   	struct drm_gem_dma_object *dma_obj;
>> +	int ret;
>>   
>> -	args->pitch = DIV_ROUND_UP(args->width * args->bpp, 8);
>> -	args->size = args->pitch * args->height;
>> +	ret = drm_mode_size_dumb(drm, args, SZ_8, 0);
>> +	if (ret)
>> +		return ret;
>>   
>>   	dma_obj = drm_gem_dma_create_with_handle(file_priv, drm, args->size,
>>   						 &args->handle);
>> diff --git a/drivers/gpu/drm/imx/ipuv3/imx-drm-core.c b/drivers/gpu/drm/imx/ipuv3/imx-drm-core.c
>> index ec5fd9a01f1e..e7025df7b978 100644
>> --- a/drivers/gpu/drm/imx/ipuv3/imx-drm-core.c
>> +++ b/drivers/gpu/drm/imx/ipuv3/imx-drm-core.c
>> @@ -145,6 +145,8 @@ static int imx_drm_dumb_create(struct drm_file *file_priv,
>>   	int ret;
>>   
>>   	args->width = ALIGN(width, 8);
>> +	args->pitch = DIV_ROUND_UP(args->width * args->bpp, 8);
>> +	args->size = args->pitch * args->height;
>>   
>>   	ret = drm_gem_dma_dumb_create(file_priv, drm, args);
>>   	if (ret)
> Won't the pitch and size just be overwritten by the
> drm_gem_dma_dumb_create() call?

Right, looks like it. Thanks for looking over this. The call to 
drm_gem_dma_dumb_create() needs to be changed 
drm_gem_dma_dumb_create_internal(). The latter doesn't modify the 
arguments besides some sanity checks. BTW patch 10 cleans up imx 
entirely. Best regards Thomas
>
>   Tomi
>

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)


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