Re: [PATCH v3 02/25] drm/dumb-buffers: Provide helper to set pitch and size

Thomas Zimmermann
2025-02-19T08:22:27Z

Hi

Am 18.02.25 um 20:32 schrieb Geert Uytterhoeven:
[...]
>> + args->bpp);
>> + fallthrough;
>> + case 12:
>> + case 15:
>> + case 30: /* see drm_gem_afbc_get_bpp() */
>> + case 10:
> Perhaps keep them sorted numerically?

The first block comes from the afbc helper; the second block from Mesa;
hence the odd order. I'll reorder and comment each case individually.

>
>> + case 64: /* used by Mesa */
>> + pitch = args->width * DIV_ROUND_UP(args->bpp, SZ_8);
>> + break;
>> + }
>> + }
>> +
>> + if (!pitch || pitch > U32_MAX)
>> + return -EINVAL;
>> +
>> + args->pitch = pitch;
>> +
>> + return drm_mode_align_dumb(args, pitch_align, size_align);
>> +}
>> +EXPORT_SYMBOL(drm_mode_size_dumb);
>> +
>> int drm_mode_create_dumb(struct drm_device *dev,
>> struct drm_mode_create_dumb *args,
>> struct drm_file *file_priv)
>> diff --git a/include/drm/drm_dumb_buffers.h b/include/drm/drm_dumb_buffers.h
>> new file mode 100644
>> index 000000000000..6fe36004b19d
>> --- /dev/null
>> +++ b/include/drm/drm_dumb_buffers.h
>> @@ -0,0 +1,14 @@
>> +/* SPDX-License-Identifier: MIT */
>> +
>> +#ifndef __DRM_DUMB_BUFFERS_H__
>> +#define __DRM_DUMB_BUFFERS_H__
>> +
>> +struct drm_device;
>> +struct drm_mode_create_dumb;
>> +
>> +int drm_mode_size_dumb(struct drm_device *dev,
>> + struct drm_mode_create_dumb *args,
>> + unsigned long pitch_align,
>> + unsigned long size_align);
>> +
>> +#endif
>> diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
>> index c082810c08a8..eea09103b1a6 100644
>> --- a/include/uapi/drm/drm_mode.h
>> +++ b/include/uapi/drm/drm_mode.h
>> @@ -1058,7 +1058,7 @@ struct drm_mode_crtc_page_flip_target {
>> * struct drm_mode_create_dumb - Create a KMS dumb buffer for scanout.
>> * @height: buffer height in pixels
>> * @width: buffer width in pixels
>> - * @bpp: bits per pixel
>> + * @bpp: color mode
>> * @flags: must be zero
>> * @handle: buffer object handle
>> * @pitch: number of bytes between two consecutive lines
>> @@ -1066,6 +1066,50 @@ struct drm_mode_crtc_page_flip_target {
>> *
>> * User-space fills @height, @width, @bpp and @flags. If the IOCTL succeeds,
>> * the kernel fills @handle, @pitch and @size.
>> + *
>> + * The value of @bpp is a color-mode number describing a specific format
>> + * or a variant thereof. The value often corresponds to the number of bits
>> + * per pixel for most modes, although there are exceptions. Each color mode
>> + * maps to a DRM format plus a number of modes with similar pixel layout.
>> + * Framebuffer layout is always linear.
>> + *
>> + * Support for all modes and formats is optional. Even if dumb-buffer
>> + * creation with a certain color mode succeeds, it is not guaranteed that
>> + * the DRM driver supports any of the related formats. Most drivers support
>> + * a color mode of 32 with a format of DRM_FORMAT_XRGB8888 on their primary
>> + * plane.
>> + *
>> + * +------------+------------------------+------------------------+
>> + * | Color mode | Framebuffer format | Compatibles |
>> + * +============+========================+========================+
>> + * | 32 | * DRM_FORMAT_XRGB8888 | * DRM_FORMAT_XBGR8888 |
>> + * | | | * DRM_FORMAT_RGBX8888 |
>> + * | | | * DRM_FORMAT_BGRX8888 |
>> + * +------------+------------------------+------------------------+
>> + * | 24 | * DRM_FORMAT_RGB888 | * DRM_FORMAT_BGR888 |
>> + * +------------+------------------------+------------------------+
>> + * | 16 | * DRM_FORMAT_RGB565 | * DRM_FORMAT_BGR565 |
>> + * +------------+------------------------+------------------------+
>> + * | 15 | * DRM_FORMAT_XRGB1555 | * DRM_FORMAT_XBGR1555 |
>> + * | | | * DRM_FORMAT_RGBX1555 |
>> + * | | | * DRM_FORMAT_BGRX1555 |
>> + * +------------+------------------------+------------------------+
>> + * | 8 | * DRM_FORMAT_C8 | * DRM_FORMAT_R8 |
> + DRM_FORMAT_D8? (and 4/2/1 below)

Right, missed that.

>
> And DRM_FORMAT_Y8, if/when Tomi's series introducing that is accepted...

Sure, if it is compatible, it can also go into the third column.

Best regards
Thomas

>
>> + * +------------+------------------------+------------------------+
>> + * | 4 | * DRM_FORMAT_C4 | * DRM_FORMAT_R4 |
>> + * +------------+------------------------+------------------------+
>> + * | 2 | * DRM_FORMAT_C2 | * DRM_FORMAT_R2 |
>> + * +------------+------------------------+------------------------+
>> + * | 1 | * DRM_FORMAT_C1 | * DRM_FORMAT_R1 |
>> + * +------------+------------------------+------------------------+
>> + *
>> + * Color modes of 10, 12, 15, 30 and 64 are only supported for use by
>> + * legacy user space. Please don't use them in new code. Other modes
>> + * are not support.
>> + *
>> + * Do not attempt to allocate anything but linear framebuffer memory
>> + * with single-plane RGB data. Allocation of other framebuffer
>> + * layouts requires dedicated ioctls in the respective DRM driver.
>> */
>> struct drm_mode_create_dumb {
>> __u32 height;
> Gr{oetje,eeting}s,
>
> Geert
>

--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
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