[PATCH] drm/fourcc: Add bayer formats and modifiers

Wed Mar 4 17:36:25 UTC 2020

Hi Niklas,

Thank you for the patch.

On Fri, Feb 28, 2020 at 05:31:35PM +0100, Niklas Söderlund wrote:
> Bayer formats are used with cameras and contain green, red and blue
> components, with alternating lines of red and green, and blue and green
> pixels in different orders. For each block of 2x2 pixels there is one
> pixel with a red filter, two with a green filter, and one with a blue
> filter. The filters can be arranged in different patterns.
> 
> Add DRM fourcc formats to describe the most common Bayer formats. Also
> add a modifiers to describe the custom packing layouts used by the Intel
> IPU3 and in the MIPI (Mobile Industry Processor Interface) CSI-2
> specification.
> 
> Signed-off-by: Niklas Söderlund <niklas.soderlund at ragnatech.se>
> ---
>  include/uapi/drm/drm_fourcc.h | 95 +++++++++++++++++++++++++++++++++++
>  1 file changed, 95 insertions(+)
> 
> diff --git a/include/uapi/drm/drm_fourcc.h b/include/uapi/drm/drm_fourcc.h
> index 8bc0b31597d80737..561d5a08ffd16b69 100644
> --- a/include/uapi/drm/drm_fourcc.h
> +++ b/include/uapi/drm/drm_fourcc.h
> @@ -286,6 +286,62 @@ extern "C" {
>  #define DRM_FORMAT_YVU444	fourcc_code('Y', 'V', '2', '4') /* non-subsampled Cr (1) and Cb (2) planes */
>  
>  
> +/*
> + * Bayer formats
> + *
> + * Bayer formats contain green, red and blue components, with alternating lines
> + * of red and green, and blue and green pixels in different orders. For each
> + * block of 2x2 pixels there is one pixel with a red filter, two with a green
> + * filter, and one with a blue filter. The filters can be arranged in different
> + * patterns.
> + *
> + * For example, RGGB:
> + *	row0: RGRGRGRG...
> + *	row1: GBGBGBGB...
> + *	row3: RGRGRGRG...
> + *	row4: GBGBGBGB...
> + *	...
> + *
> + * Vendors have different methods to pack the sampling formats to increase data
> + * density. For this reason the fourcc only describes pixel sample size and the

This could be for other reasons than data density, such as for less
cumbersome memory access. I'd leave out "to increase data density".

> + * filter pattern for each block of 2x2 pixels. A modifier is needed to
> + * describe the memory layout.
> + *
> + * In addition to vendor modifiers for memory layout DRM_FORMAT_MOD_LINEAR may
> + * be used to describe a layout where all samples are placed consecutively in
> + * memory. If the sample does not fit inside a single byte, the sample storage
> + * is extended to the minimum number of (little endian) bytes that can hold the
> + * sample and any unused most-significant bits are defined as padding.

Should it be added here that padding bits are all zero?

> + *
> + * For example, SRGGB10:
> + * Each 10-bit sample is contained in 2 consecutive little endian bytes, where
> + * the 6 most-significant bits are unused.
> + */
> +
> +/* 8-bit Bayer formats */
> +#define DRM_FORMAT_SRGGB8	fourcc_code('R', 'G', 'G', 'B')
> +#define DRM_FORMAT_SGRBG8	fourcc_code('G', 'R', 'B', 'G')
> +#define DRM_FORMAT_SGBRG8	fourcc_code('G', 'B', 'R', 'G')
> +#define DRM_FORMAT_SBGGR8	fourcc_code('B', 'A', '8', '1')
> +
> +/* 10-bit Bayer formats */
> +#define DRM_FORMAT_SRGGB10	fourcc_code('R', 'G', '1', '0')
> +#define DRM_FORMAT_SGRBG10	fourcc_code('B', 'A', '1', '0')
> +#define DRM_FORMAT_SGBRG10	fourcc_code('G', 'B', '1', '0')
> +#define DRM_FORMAT_SBGGR10	fourcc_code('B', 'G', '1', '0')
> +
> +/* 12-bit Bayer formats */
> +#define DRM_FORMAT_SRGGB12	fourcc_code('R', 'G', '1', '2')
> +#define DRM_FORMAT_SGRBG12	fourcc_code('B', 'A', '1', '2')
> +#define DRM_FORMAT_SGBRG12	fourcc_code('G', 'B', '1', '2')
> +#define DRM_FORMAT_SBGGR12	fourcc_code('B', 'G', '1', '2')
> +
> +/* 14-bit Bayer formats */
> +#define DRM_FORMAT_SRGGB14	fourcc_code('R', 'G', '1', '4')
> +#define DRM_FORMAT_SGRBG14	fourcc_code('B', 'A', '1', '4')
> +#define DRM_FORMAT_SGBRG14	fourcc_code('G', 'B', '1', '4')
> +#define DRM_FORMAT_SBGGR14	fourcc_code('B', 'G', '1', '4')

The 4cc codes seemingly appear to those used in V4L2. Is that intentional?
Nothing wrong in that though, but is this a rule that's universally
followed?

> +
>  /*
>   * Format Modifiers:
>   *
> @@ -309,6 +365,7 @@ extern "C" {
>  #define DRM_FORMAT_MOD_VENDOR_BROADCOM 0x07
>  #define DRM_FORMAT_MOD_VENDOR_ARM     0x08
>  #define DRM_FORMAT_MOD_VENDOR_ALLWINNER 0x09
> +#define DRM_FORMAT_MOD_VENDOR_MIPI 0x0a
>  
>  /* add more to the end as needed */
>  
> @@ -434,6 +491,17 @@ extern "C" {
>   */
>  #define I915_FORMAT_MOD_Y_TILED_GEN12_MC_CCS fourcc_mod_code(INTEL, 7)
>  
> +
> +/*
> + * IPU3 Bayer packing layout
> + *
> + * The IPU3 raw Bayer formats use a custom packing layout where there are no
> + * gaps between each 10-bit sample. It packs 25 pixels into 32 bytes leaving
> + * the 6 most significant bits in the last byte unused. The format is little
> + * endian.

Where is endianness really specified? DRM_FORMAT_BIG_ENDIAN would seem
independent of that.

I might omit endianness definition here.

> + */
> +#define IPU3_FORMAT_MOD_PACKED fourcc_mod_code(INTEL, 8)
> +
>  /*
>   * Tiled, NV12MT, grouped in 64 (pixels) x 32 (lines) -sized macroblocks
>   *
> @@ -804,6 +872,33 @@ extern "C" {
>   */
>  #define DRM_FORMAT_MOD_ALLWINNER_TILED fourcc_mod_code(ALLWINNER, 1)
>  
> +/* Mobile Industry Processor Interface (MIPI) modifiers */
> +
> +/*
> + * MIPI CSI-2 packing layout
> + *
> + * The CSI-2 RAW formats (for example Bayer) use a different packing layout
> + * depenindg on the sample size.

"depending"

> + *
> + * - 10-bits per sample
> + *   Every four consecutive samples are packed into 5 bytes. Each of the first 4
> + *   bytes contain the 8 high order bits of the pixels, and the 5th byte
> + *   contains the 2 least-significant bits of each pixel, in the same order.
> + *
> + * - 12-bits per sample
> + *   Every two consecutive samples are packed into three bytes. Each of the
> + *   first two bytes contain the 8 high order bits of the pixels, and the third
> + *   byte contains the four least-significant bits of each pixel, in the same
> + *   order.
> + *
> + * - 14-bits per sample
> + *   Every four consecutive samples are packed into seven bytes. Each of the
> + *   first four bytes contain the eight high order bits of the pixels, and the
> + *   three following bytes contains the six least-significant bits of each
> + *   pixel, in the same order.
> + */
> +#define MIPI_FORMAT_MOD_CSI2_PACKED fourcc_mod_code(MIPI, 1)
> +
>  #if defined(__cplusplus)
>  }
>  #endif

-- 
Kind regards,

Sakari Ailus