Re: [PATCH v3 11/12] drm/sysfb: corebootdrm: Add DRM driver for coreboot framebuffers

[Tzung-Bi Shih <tzungbi@kernel.org>]

On Tue, Feb 03, 2026 at 02:52:30PM +0100, Thomas Zimmermann wrote:
> Add corebootdrm, a DRM driver for coreboot framebuffers. The driver
> supports a pre-initialized framebuffer with various packed RGB formats.
> The driver code is fairly small and uses the same logic as the other
> sysfb drivers. Most of the implementation comes from existing sysfb
> helpers.
> 
> Until now, coreboot relied on simpledrm or simplefb for boot-up graphics
> output. Initialize the platform device for corebootdrm in the same place
> in framebuffer_probe(). With a later commit, the simple-framebuffer should
> be removed.
> 
> v3:
> - comment on _HAS_LFB semantics (Tzung-Bi)
> - fix typo in commit description (Tzung-Bi)
> - comment on simple-framebuffer being obsolete for coreboot
> v2:
> - reimplement as platform driver
> - limit resources and mappings to known framebuffer memory; no
>   page alignment
> - create corebootdrm device from coreboot framebuffer code

Changelog should be after "---" otherwise it becomes part of commit message.

> +static int corebootdrm_probe(struct platform_device *pdev)
> +{
[...]
> +	if (!fb) {
> +		drm_err(dev, "coreboot framebuffer not found\n");
> +		return -EINVAL;
> +	} else if (!LB_FRAMEBUFFER_HAS_LFB(fb)) {
> +		drm_err(dev, "coreboot framebuffer entry too small\n");
> +		return -EINVAL;
> +	}
> +
> +	/*
> +	 * Hardware settings
> +	 */
> +
> +	format = corebootdrm_get_format_fb(dev, fb);
> +	if (!format)
> +		return -EINVAL;
> +	width = corebootdrm_get_width_fb(dev, fb);
> +	if (width < 0)
> +		return width;
> +	height = corebootdrm_get_height_fb(dev, fb);
> +	if (height < 0)
> +		return height;
[...]
> diff --git a/include/linux/coreboot.h b/include/linux/coreboot.h
> index 5746b99a070d..b51665165f9f 100644
> --- a/include/linux/coreboot.h
> +++ b/include/linux/coreboot.h
> @@ -14,6 +14,7 @@
>  
>  #include <linux/compiler_attributes.h>
>  #include <linux/types.h>
> +#include <linux/stddef.h>

Move it before types.h?  's' vs. 't'.

> +/*
> + * True if the coreboot-provided data is large enough to hold information
> + * on the linear framebuffer. False otherwise.
> + */
> +#define LB_FRAMEBUFFER_HAS_LFB(__fb) \
> +	((__fb)->size >= offsetofend(struct lb_framebuffer, reserved_mask_size))
> +

To make sure I understand, do you mean:

- The __fb->size is possibly less than sizeof(struct lb_framebuffer).
  LB_FRAMEBUFFER_HAS_LFB() is for checking the following fields
  (e.g. fb->x_resolution) are available?

    struct lb_framebuffer {
    	u32 tag;
    	u32 size;

    	u64 physical_address;
    	u32 x_resolution;
    	u32 y_resolution;
    	u32 bytes_per_line;
    	u8  bits_per_pixel;
    	u8  red_mask_pos;
    	u8  red_mask_size;
    	u8  green_mask_pos;
    	u8  green_mask_size;
    	u8  blue_mask_pos;
    	u8  blue_mask_size;
    	u8  reserved_mask_pos;
    	u8  reserved_mask_size;
    };

- If answer of the previous question is yes, the next question: does
  LB_FRAMEBUFFER_HAS_LFB() needs to check up to `reserved_mask_size`?
  As in the patch, it only accesses up to `blue_mask_size`.