Re: [PATCH v6 03/25] drm/gem-dma: Compute dumb-buffer sizes with drm_mode_size_dumb()

Ludovic.Desroches
2025-11-25T14:40:09Z

On 8/21/25 10:17, 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.
>
> v5:
> - avoid reset of arguments (Tomi)
>
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
> ---
> drivers/gpu/drm/drm_gem_dma_helper.c | 7 +++++--
> drivers/gpu/drm/imx/ipuv3/imx-drm-core.c | 4 +++-
> 2 files changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_gem_dma_helper.c b/drivers/gpu/drm/drm_gem_dma_helper.c
> index 4f0320df858f..ab1a70b1d6f1 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;

Hi,

Was it intentional for this change to alter the pitch?

The alignment requirement has been updated—from 8-bit alignment to
64-bit alignment. Since the pitch is expressed in bytes, we should pass
SZ_1 instead of SZ_8 for hw_patch_align.

For example, for an 850×480 framebuffer at 16 bpp, the pitch should be
1700 bytes. With the new alignment, the pitch becomes 1704 bytes.

Please let me know if you’d like me to submit a fix.

Regards,
Ludovic

>
> 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..af4a30311e18 100644
> --- a/drivers/gpu/drm/imx/ipuv3/imx-drm-core.c
> +++ b/drivers/gpu/drm/imx/ipuv3/imx-drm-core.c
> @@ -145,8 +145,10 @@ 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);
> + ret = drm_gem_dma_dumb_create_internal(file_priv, drm, args);
> if (ret)
> return ret;
>