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Date: Mon, 25 Mar 2024 10:56:12 -0300
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Subject: Re: [PATCH v5 04/16] drm/vkms: Add typedef and documentation for
 pixel_read and pixel_write functions
To: Louis Chauvet <louis.chauvet@bootlin.com>,
 Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>,
 Melissa Wen <melissa.srw@gmail.com>,
 Haneen Mohammed <hamohammed.sa@gmail.com>, Daniel Vetter <daniel@ffwll.ch>,
 Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
 Maxime Ripard <mripard@kernel.org>, Thomas Zimmermann <tzimmermann@suse.de>,
 David Airlie <airlied@gmail.com>, arthurgrillo@riseup.net,
 Jonathan Corbet <corbet@lwn.net>, pekka.paalanen@haloniitty.fi
Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
 jeremie.dautheribes@bootlin.com, miquel.raynal@bootlin.com,
 thomas.petazzoni@bootlin.com, seanpaul@google.com, marcheu@google.com,
 nicolejadeyee@google.com
References: <20240313-yuv-v5-0-e610cbd03f52@bootlin.com>
 <20240313-yuv-v5-4-e610cbd03f52@bootlin.com>
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On 3/13/24 14:44, Louis Chauvet wrote:
> Introduce two typedefs: pixel_read_t and pixel_write_t. It allows the
> compiler to check if the passed functions take the correct arguments.
> Such typedefs will help ensuring consistency across the code base in
> case of update of these prototypes.
> 
> Rename input/output variable in a consistent way between read_line and
> write_line.
> 
> A warn has been added in get_pixel_*_function to alert when an unsupported
> pixel format is requested. As those formats are checked before
> atomic_update callbacks, it should never append.
> 
> Document for those typedefs.
> 
> Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>
> ---
>   drivers/gpu/drm/vkms/vkms_drv.h     |  23 ++++++-
>   drivers/gpu/drm/vkms/vkms_formats.c | 124 +++++++++++++++++++++---------------
>   drivers/gpu/drm/vkms/vkms_formats.h |   4 +-
>   drivers/gpu/drm/vkms/vkms_plane.c   |   2 +-
>   4 files changed, 95 insertions(+), 58 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vkms/vkms_drv.h b/drivers/gpu/drm/vkms/vkms_drv.h
> index 18086423a3a7..4bfc62d26f08 100644
> --- a/drivers/gpu/drm/vkms/vkms_drv.h
> +++ b/drivers/gpu/drm/vkms/vkms_drv.h
> @@ -53,12 +53,31 @@ struct line_buffer {
>   	struct pixel_argb_u16 *pixels;
>   };
>   
> +/**
> + * typedef pixel_write_t - These functions are used to read a pixel from a
> + * `struct pixel_argb_u16*`, convert it in a specific format and write it in the @dst_pixels
> + * buffer.

Your brief description looks a bit big to me. Also, take a look at the 
cross-references docs [1].

[1] 
https://docs.kernel.org/doc-guide/kernel-doc.html#highlights-and-cross-references

> + *
> + * @out_pixel: destination address to write the pixel
> + * @in_pixel: pixel to write
> + */
> +typedef void (*pixel_write_t)(u8 *out_pixel, struct pixel_argb_u16 *in_pixel);
> +
>   struct vkms_writeback_job {
>   	struct iosys_map data[DRM_FORMAT_MAX_PLANES];
>   	struct vkms_frame_info wb_frame_info;
> -	void (*pixel_write)(u8 *dst_pixels, struct pixel_argb_u16 *in_pixel);
> +	pixel_write_t pixel_write;
>   };
>   
> +/**
> + * typedef pixel_read_t - These functions are used to read a pixel in the source frame,
> + * convert it to `struct pixel_argb_u16` and write it to @out_pixel.

Same.

> + *
> + * @in_pixel: Pointer to the pixel to read
> + * @out_pixel: Pointer to write the converted pixel

s/Pointer/pointer

> + */
> +typedef void (*pixel_read_t)(u8 *in_pixel, struct pixel_argb_u16 *out_pixel);
> +
>   /**
>    * vkms_plane_state - Driver specific plane state
>    * @base: base plane state
> @@ -69,7 +88,7 @@ struct vkms_writeback_job {
>   struct vkms_plane_state {
>   	struct drm_shadow_plane_state base;
>   	struct vkms_frame_info *frame_info;
> -	void (*pixel_read)(u8 *src_buffer, struct pixel_argb_u16 *out_pixel);
> +	pixel_read_t pixel_read;
>   };
>   
>   struct vkms_plane {
> diff --git a/drivers/gpu/drm/vkms/vkms_formats.c b/drivers/gpu/drm/vkms/vkms_formats.c
> index 6e3dc8682ff9..55a4365d21a4 100644
> --- a/drivers/gpu/drm/vkms/vkms_formats.c
> +++ b/drivers/gpu/drm/vkms/vkms_formats.c
> @@ -76,7 +76,7 @@ static int get_x_position(const struct vkms_frame_info *frame_info, int limit, i
>    * They are used in the `vkms_compose_row` function to handle multiple formats.
>    */
>   
> -static void ARGB8888_to_argb_u16(u8 *src_pixels, struct pixel_argb_u16 *out_pixel)
> +static void ARGB8888_to_argb_u16(u8 *in_pixel, struct pixel_argb_u16 *out_pixel)
>   {
>   	/*
>   	 * The 257 is the "conversion ratio". This number is obtained by the
> @@ -84,48 +84,48 @@ static void ARGB8888_to_argb_u16(u8 *src_pixels, struct pixel_argb_u16 *out_pixe
>   	 * the best color value in a pixel format with more possibilities.
>   	 * A similar idea applies to others RGB color conversions.
>   	 */
> -	out_pixel->a = (u16)src_pixels[3] * 257;
> -	out_pixel->r = (u16)src_pixels[2] * 257;
> -	out_pixel->g = (u16)src_pixels[1] * 257;
> -	out_pixel->b = (u16)src_pixels[0] * 257;
> +	out_pixel->a = (u16)in_pixel[3] * 257;
> +	out_pixel->r = (u16)in_pixel[2] * 257;
> +	out_pixel->g = (u16)in_pixel[1] * 257;
> +	out_pixel->b = (u16)in_pixel[0] * 257;
>   }
>   
> -static void XRGB8888_to_argb_u16(u8 *src_pixels, struct pixel_argb_u16 *out_pixel)
> +static void XRGB8888_to_argb_u16(u8 *in_pixel, struct pixel_argb_u16 *out_pixel)
>   {
>   	out_pixel->a = (u16)0xffff;
> -	out_pixel->r = (u16)src_pixels[2] * 257;
> -	out_pixel->g = (u16)src_pixels[1] * 257;
> -	out_pixel->b = (u16)src_pixels[0] * 257;
> +	out_pixel->r = (u16)in_pixel[2] * 257;
> +	out_pixel->g = (u16)in_pixel[1] * 257;
> +	out_pixel->b = (u16)in_pixel[0] * 257;
>   }
>   
> -static void ARGB16161616_to_argb_u16(u8 *src_pixels, struct pixel_argb_u16 *out_pixel)
> +static void ARGB16161616_to_argb_u16(u8 *in_pixel, struct pixel_argb_u16 *out_pixel)
>   {
> -	u16 *pixels = (u16 *)src_pixels;
> +	u16 *pixel = (u16 *)in_pixel;
>   
> -	out_pixel->a = le16_to_cpu(pixels[3]);
> -	out_pixel->r = le16_to_cpu(pixels[2]);
> -	out_pixel->g = le16_to_cpu(pixels[1]);
> -	out_pixel->b = le16_to_cpu(pixels[0]);
> +	out_pixel->a = le16_to_cpu(pixel[3]);
> +	out_pixel->r = le16_to_cpu(pixel[2]);
> +	out_pixel->g = le16_to_cpu(pixel[1]);
> +	out_pixel->b = le16_to_cpu(pixel[0]);
>   }
>   
> -static void XRGB16161616_to_argb_u16(u8 *src_pixels, struct pixel_argb_u16 *out_pixel)
> +static void XRGB16161616_to_argb_u16(u8 *in_pixel, struct pixel_argb_u16 *out_pixel)
>   {
> -	u16 *pixels = (u16 *)src_pixels;
> +	u16 *pixel = (u16 *)in_pixel;
>   
>   	out_pixel->a = (u16)0xffff;
> -	out_pixel->r = le16_to_cpu(pixels[2]);
> -	out_pixel->g = le16_to_cpu(pixels[1]);
> -	out_pixel->b = le16_to_cpu(pixels[0]);
> +	out_pixel->r = le16_to_cpu(pixel[2]);
> +	out_pixel->g = le16_to_cpu(pixel[1]);
> +	out_pixel->b = le16_to_cpu(pixel[0]);
>   }
>   
> -static void RGB565_to_argb_u16(u8 *src_pixels, struct pixel_argb_u16 *out_pixel)
> +static void RGB565_to_argb_u16(u8 *in_pixel, struct pixel_argb_u16 *out_pixel)
>   {
> -	u16 *pixels = (u16 *)src_pixels;
> +	u16 *pixel = (u16 *)in_pixel;
>   
>   	s64 fp_rb_ratio = drm_fixp_div(drm_int2fixp(65535), drm_int2fixp(31));
>   	s64 fp_g_ratio = drm_fixp_div(drm_int2fixp(65535), drm_int2fixp(63));
>   
> -	u16 rgb_565 = le16_to_cpu(*pixels);
> +	u16 rgb_565 = le16_to_cpu(*pixel);
>   	s64 fp_r = drm_int2fixp((rgb_565 >> 11) & 0x1f);
>   	s64 fp_g = drm_int2fixp((rgb_565 >> 5) & 0x3f);
>   	s64 fp_b = drm_int2fixp(rgb_565 & 0x1f);
> @@ -169,12 +169,12 @@ void vkms_compose_row(struct line_buffer *stage_buffer, struct vkms_plane_state
>   
>   /*
>    * The following functions take one argb_u16 pixel and convert it to a specific format. The
> - * result is stored in @dst_pixels.
> + * result is stored in @out_pixel.
>    *
>    * They are used in the `vkms_writeback_row` to convert and store a pixel from the src_buffer to
>    * the writeback buffer.
>    */
> -static void argb_u16_to_ARGB8888(u8 *dst_pixels, struct pixel_argb_u16 *in_pixel)
> +static void argb_u16_to_ARGB8888(u8 *out_pixel, struct pixel_argb_u16 *in_pixel)
>   {
>   	/*
>   	 * This sequence below is important because the format's byte order is
> @@ -186,43 +186,43 @@ static void argb_u16_to_ARGB8888(u8 *dst_pixels, struct pixel_argb_u16 *in_pixel
>   	 * | Addr + 2 | = Red channel
>   	 * | Addr + 3 | = Alpha channel
>   	 */
> -	dst_pixels[3] = DIV_ROUND_CLOSEST(in_pixel->a, 257);
> -	dst_pixels[2] = DIV_ROUND_CLOSEST(in_pixel->r, 257);
> -	dst_pixels[1] = DIV_ROUND_CLOSEST(in_pixel->g, 257);
> -	dst_pixels[0] = DIV_ROUND_CLOSEST(in_pixel->b, 257);
> +	out_pixel[3] = DIV_ROUND_CLOSEST(in_pixel->a, 257);
> +	out_pixel[2] = DIV_ROUND_CLOSEST(in_pixel->r, 257);
> +	out_pixel[1] = DIV_ROUND_CLOSEST(in_pixel->g, 257);
> +	out_pixel[0] = DIV_ROUND_CLOSEST(in_pixel->b, 257);
>   }
>   
> -static void argb_u16_to_XRGB8888(u8 *dst_pixels, struct pixel_argb_u16 *in_pixel)
> +static void argb_u16_to_XRGB8888(u8 *out_pixel, struct pixel_argb_u16 *in_pixel)
>   {
> -	dst_pixels[3] = 0xff;
> -	dst_pixels[2] = DIV_ROUND_CLOSEST(in_pixel->r, 257);
> -	dst_pixels[1] = DIV_ROUND_CLOSEST(in_pixel->g, 257);
> -	dst_pixels[0] = DIV_ROUND_CLOSEST(in_pixel->b, 257);
> +	out_pixel[3] = 0xff;
> +	out_pixel[2] = DIV_ROUND_CLOSEST(in_pixel->r, 257);
> +	out_pixel[1] = DIV_ROUND_CLOSEST(in_pixel->g, 257);
> +	out_pixel[0] = DIV_ROUND_CLOSEST(in_pixel->b, 257);
>   }
>   
> -static void argb_u16_to_ARGB16161616(u8 *dst_pixels, struct pixel_argb_u16 *in_pixel)
> +static void argb_u16_to_ARGB16161616(u8 *out_pixel, struct pixel_argb_u16 *in_pixel)
>   {
> -	u16 *pixels = (u16 *)dst_pixels;
> +	u16 *pixel = (u16 *)out_pixel;
>   
> -	pixels[3] = cpu_to_le16(in_pixel->a);
> -	pixels[2] = cpu_to_le16(in_pixel->r);
> -	pixels[1] = cpu_to_le16(in_pixel->g);
> -	pixels[0] = cpu_to_le16(in_pixel->b);
> +	pixel[3] = cpu_to_le16(in_pixel->a);
> +	pixel[2] = cpu_to_le16(in_pixel->r);
> +	pixel[1] = cpu_to_le16(in_pixel->g);
> +	pixel[0] = cpu_to_le16(in_pixel->b);
>   }
>   
> -static void argb_u16_to_XRGB16161616(u8 *dst_pixels, struct pixel_argb_u16 *in_pixel)
> +static void argb_u16_to_XRGB16161616(u8 *out_pixel, struct pixel_argb_u16 *in_pixel)
>   {
> -	u16 *pixels = (u16 *)dst_pixels;
> +	u16 *pixel = (u16 *)out_pixel;
>   
> -	pixels[3] = 0xffff;
> -	pixels[2] = cpu_to_le16(in_pixel->r);
> -	pixels[1] = cpu_to_le16(in_pixel->g);
> -	pixels[0] = cpu_to_le16(in_pixel->b);
> +	pixel[3] = 0xffff;
> +	pixel[2] = cpu_to_le16(in_pixel->r);
> +	pixel[1] = cpu_to_le16(in_pixel->g);
> +	pixel[0] = cpu_to_le16(in_pixel->b);
>   }
>   
> -static void argb_u16_to_RGB565(u8 *dst_pixels, struct pixel_argb_u16 *in_pixel)
> +static void argb_u16_to_RGB565(u8 *out_pixel, struct pixel_argb_u16 *in_pixel)
>   {
> -	u16 *pixels = (u16 *)dst_pixels;
> +	u16 *pixel = (u16 *)out_pixel;
>   
>   	s64 fp_rb_ratio = drm_fixp_div(drm_int2fixp(65535), drm_int2fixp(31));
>   	s64 fp_g_ratio = drm_fixp_div(drm_int2fixp(65535), drm_int2fixp(63));
> @@ -235,7 +235,7 @@ static void argb_u16_to_RGB565(u8 *dst_pixels, struct pixel_argb_u16 *in_pixel)
>   	u16 g = drm_fixp2int(drm_fixp_div(fp_g, fp_g_ratio));
>   	u16 b = drm_fixp2int(drm_fixp_div(fp_b, fp_rb_ratio));
>   
> -	*pixels = cpu_to_le16(r << 11 | g << 5 | b);
> +	*pixel = cpu_to_le16(r << 11 | g << 5 | b);
>   }
>   
>   /**
> @@ -266,7 +266,7 @@ void vkms_writeback_row(struct vkms_writeback_job *wb,
>    *
>    * @format: DRM_FORMAT_* value for which to obtain a conversion function (see [drm_fourcc.h])
>    */
> -void *get_pixel_conversion_function(u32 format)
> +pixel_read_t get_pixel_read_function(u32 format)
>   {
>   	switch (format) {
>   	case DRM_FORMAT_ARGB8888:
> @@ -280,7 +280,16 @@ void *get_pixel_conversion_function(u32 format)
>   	case DRM_FORMAT_RGB565:
>   		return &RGB565_to_argb_u16;
>   	default:
> -		return NULL;
> +		/*
> +		 * This is a bug in vkms_plane_atomic_check. All the supported

s/vkms_plane_atomic_check/vkms_plane_atomic_check()

Best Regards,
- Maíra

> +		 * format must:
> +		 * - Be listed in vkms_formats in vkms_plane.c
> +		 * - Have a pixel_read callback defined here
> +		 */
> +		WARN(true,
> +		     "Pixel format %p4cc is not supported by VKMS planes. This is a kernel bug, atomic check must forbid this configuration.\n",
> +		     &format);
> +		return (pixel_read_t)NULL;
>   	}
>   }
>   
> @@ -291,7 +300,7 @@ void *get_pixel_conversion_function(u32 format)
>    *
>    * @format: DRM_FORMAT_* value for which to obtain a conversion function (see [drm_fourcc.h])
>    */
> -void *get_pixel_write_function(u32 format)
> +pixel_write_t get_pixel_write_function(u32 format)
>   {
>   	switch (format) {
>   	case DRM_FORMAT_ARGB8888:
> @@ -305,6 +314,15 @@ void *get_pixel_write_function(u32 format)
>   	case DRM_FORMAT_RGB565:
>   		return &argb_u16_to_RGB565;
>   	default:
> -		return NULL;
> +		/*
> +		 * This is a bug in vkms_writeback_atomic_check. All the supported
> +		 * format must:
> +		 * - Be listed in vkms_wb_formats in vkms_writeback.c
> +		 * - Have a pixel_write callback defined here
> +		 */
> +		WARN(true,
> +		     "Pixel format %p4cc is not supported by VKMS writeback. This is a kernel bug, atomic check must forbid this configuration.\n",
> +		     &format);
> +		return (pixel_write_t)NULL;
>   	}
>   }
> diff --git a/drivers/gpu/drm/vkms/vkms_formats.h b/drivers/gpu/drm/vkms/vkms_formats.h
> index cf59c2ed8e9a..3ecea4563254 100644
> --- a/drivers/gpu/drm/vkms/vkms_formats.h
> +++ b/drivers/gpu/drm/vkms/vkms_formats.h
> @@ -5,8 +5,8 @@
>   
>   #include "vkms_drv.h"
>   
> -void *get_pixel_conversion_function(u32 format);
> +pixel_read_t get_pixel_read_function(u32 format);
>   
> -void *get_pixel_write_function(u32 format);
> +pixel_write_t get_pixel_write_function(u32 format);
>   
>   #endif /* _VKMS_FORMATS_H_ */
> diff --git a/drivers/gpu/drm/vkms/vkms_plane.c b/drivers/gpu/drm/vkms/vkms_plane.c
> index 21b5adfb44aa..10e9b23dab28 100644
> --- a/drivers/gpu/drm/vkms/vkms_plane.c
> +++ b/drivers/gpu/drm/vkms/vkms_plane.c
> @@ -125,7 +125,7 @@ static void vkms_plane_atomic_update(struct drm_plane *plane,
>   	drm_rect_rotate(&frame_info->rotated, drm_rect_width(&frame_info->rotated),
>   			drm_rect_height(&frame_info->rotated), frame_info->rotation);
>   
> -	vkms_plane_state->pixel_read = get_pixel_conversion_function(fmt);
> +	vkms_plane_state->pixel_read = get_pixel_read_function(fmt);
>   }
>   
>   static int vkms_plane_atomic_check(struct drm_plane *plane,
>