[PATCH v2 23/25] drm/xe: Compute dumb-buffer sizes with drm_mode_size_dumb()

[Thomas Zimmermann]

Hi


Am 09.01.25 um 17:05 schrieb Matthew Auld:
> On 09/01/2025 14:57, 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. Align the
>> buffer size according to hardware requirements.
>>
>> Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
>> Cc: Lucas De Marchi <lucas.demarchi at intel.com>
>> Cc: "Thomas Hellström" <thomas.hellstrom at linux.intel.com>
>> Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
>> ---
>>   drivers/gpu/drm/xe/xe_bo.c | 8 ++++----
>>   1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
>> index e6c896ad5602..d75e3c39ab14 100644
>> --- a/drivers/gpu/drm/xe/xe_bo.c
>> +++ b/drivers/gpu/drm/xe/xe_bo.c
>> @@ -8,6 +8,7 @@
>>   #include <linux/dma-buf.h>
>>     #include <drm/drm_drv.h>
>> +#include <drm/drm_dumb_buffers.h>
>>   #include <drm/drm_gem_ttm_helper.h>
>>   #include <drm/drm_managed.h>
>>   #include <drm/ttm/ttm_device.h>
>> @@ -2535,14 +2536,13 @@ int xe_bo_dumb_create(struct drm_file 
>> *file_priv,
>>       struct xe_device *xe = to_xe_device(dev);
>>       struct xe_bo *bo;
>>       uint32_t handle;
>> -    int cpp = DIV_ROUND_UP(args->bpp, 8);
>>       int err;
>>       u32 page_size = max_t(u32, PAGE_SIZE,
>>           xe->info.vram_flags & XE_VRAM_FLAGS_NEED64K ? SZ_64K : SZ_4K);
>>   -    args->pitch = ALIGN(args->width * cpp, 64);
>> -    args->size = ALIGN(mul_u32_u32(args->pitch, args->height),
>> -               page_size);
>> +    err = drm_mode_size_dumb(dev, args, SZ_64, page_size);
>
> AFAICT this looks to change the behaviour, where u64 size was 
> technically possible and was allowed given that args->size is u64, but 
> this helper is limiting the size to u32. Is that intentional? If so, 
> we should probably make that clear in the commit message.

That's an interesting observation; thanks. The ioctl's internal checks 
have always limited the size to 32 bit. [1] I think it is not supposed 
to be larger than that. We can change the helper to support 64-bit sizes 
as well.

Having said that, is there any use case? Dumb buffers are for software 
rendering only. Allocating more than a few dozen MiB seems like a 
mistake. Maybe we should rather limit the allowed allocation size instead?

Best regards
Thomas

[1] 
https://elixir.bootlin.com/linux/v6.12.6/source/drivers/gpu/drm/drm_dumb_buffers.c#L82

>
>> +    if (err)
>> +        return err;
>>         bo = xe_bo_create_user(xe, NULL, NULL, args->size,
>>                      DRM_XE_GEM_CPU_CACHING_WC,
>

-- 
--
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)