[PATCH v2 3/4] drm/tinydrm: Add tinydrm_xrgb8888_to_gray8() helper

[Daniel Vetter]

On Thu, Jun 08, 2017 at 05:14:34PM +0200, Noralf Trønnes wrote:
> Drm has no monochrome or greyscale support so add a conversion
> from the common format XR24.
> 
> Also reorder includes into the common order.
> 
> Signed-off-by: Noralf Trønnes <noralf at tronnes.org>
> ---
>  drivers/gpu/drm/tinydrm/core/tinydrm-helpers.c | 74 +++++++++++++++++++++++++-
>  include/drm/tinydrm/tinydrm-helpers.h          |  1 +
>  2 files changed, 73 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/tinydrm/core/tinydrm-helpers.c b/drivers/gpu/drm/tinydrm/core/tinydrm-helpers.c
> index d4cda33..75808bb 100644
> --- a/drivers/gpu/drm/tinydrm/core/tinydrm-helpers.c
> +++ b/drivers/gpu/drm/tinydrm/core/tinydrm-helpers.c
> @@ -7,13 +7,15 @@
>   * (at your option) any later version.
>   */
>  
> -#include <drm/tinydrm/tinydrm.h>
> -#include <drm/tinydrm/tinydrm-helpers.h>
>  #include <linux/backlight.h>
> +#include <linux/dma-buf.h>
>  #include <linux/pm.h>
>  #include <linux/spi/spi.h>
>  #include <linux/swab.h>
>  
> +#include <drm/tinydrm/tinydrm.h>
> +#include <drm/tinydrm/tinydrm-helpers.h>
> +
>  static unsigned int spi_max;
>  module_param(spi_max, uint, 0400);
>  MODULE_PARM_DESC(spi_max, "Set a lower SPI max transfer size");
> @@ -181,6 +183,74 @@ void tinydrm_xrgb8888_to_rgb565(u16 *dst, void *vaddr,
>  EXPORT_SYMBOL(tinydrm_xrgb8888_to_rgb565);
>  
>  /**
> + * tinydrm_xrgb8888_to_gray8 - Convert XRGB8888 to grayscale
> + * @dst: 8-bit grayscale destination buffer
> + * @fb: DRM framebuffer
> + *
> + * Drm doesn't have native monochrome or grayscale support.
> + * Such drivers can announce the commonly supported XR24 format to userspace
> + * and use this function to convert to the native format.
> + *
> + * Monochrome drivers will use the most significant bit,
> + * where 1 means foreground color and 0 background color.
> + *
> + * ITU BT.601 is used for the RGB -> luma (brightness) conversion.
> + *
> + * Returns:
> + * Zero on success, negative error code on failure.
> + */
> +int tinydrm_xrgb8888_to_gray8(u8 *dst, struct drm_framebuffer *fb)

I think it's ok to use this for backwards compat reasons with userspace
that simply expects xrgb8888, but adding monochrome fourcc codes to drm
isn't hard, and I think would be better to do that here.

There's also my comment from earlier that too much of tinydrm is in
tinydrm, and maybe we should move some of it out (we already have
tinydrm_xrgb8888_to_rgb565). But looks ok otherwise.

Acked-by: Daniel Vetter <daniel.vetter at ffwll.ch>

Daniel


> +{
> +	struct drm_gem_cma_object *cma_obj = drm_fb_cma_get_gem_obj(fb, 0);
> +	struct dma_buf_attachment *import_attach = cma_obj->base.import_attach;
> +	unsigned int x, y, pitch = fb->pitches[0];
> +	int ret = 0;
> +	void *buf;
> +	u32 *src;
> +
> +	if (WARN_ON(fb->format->format != DRM_FORMAT_XRGB8888))
> +		return -EINVAL;
> +	/*
> +	 * The cma memory is write-combined so reads are uncached.
> +	 * Speed up by fetching one line at a time.
> +	 */
> +	buf = kmalloc(pitch, GFP_KERNEL);
> +	if (!buf)
> +		return -ENOMEM;
> +
> +	if (import_attach) {
> +		ret = dma_buf_begin_cpu_access(import_attach->dmabuf,
> +					       DMA_FROM_DEVICE);
> +		if (ret)
> +			goto err_free;
> +	}
> +
> +	for (y = 0; y < fb->height; y++) {
> +		src = cma_obj->vaddr + (y * pitch);
> +		memcpy(buf, src, pitch);
> +		src = buf;
> +		for (x = 0; x < fb->width; x++) {
> +			u8 r = (*src & 0x00ff0000) >> 16;
> +			u8 g = (*src & 0x0000ff00) >> 8;
> +			u8 b =  *src & 0x000000ff;
> +
> +			/* ITU BT.601: Y = 0.299 R + 0.587 G + 0.114 B */
> +			*dst++ = (3 * r + 6 * g + b) / 10;
> +			src++;
> +		}
> +	}
> +
> +	if (import_attach)
> +		ret = dma_buf_end_cpu_access(import_attach->dmabuf,
> +					     DMA_FROM_DEVICE);
> +err_free:
> +	kfree(buf);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL(tinydrm_xrgb8888_to_gray8);
> +
> +/**
>   * tinydrm_of_find_backlight - Find backlight device in device-tree
>   * @dev: Device
>   *
> diff --git a/include/drm/tinydrm/tinydrm-helpers.h b/include/drm/tinydrm/tinydrm-helpers.h
> index 9b9b6cf..a6c387f 100644
> --- a/include/drm/tinydrm/tinydrm-helpers.h
> +++ b/include/drm/tinydrm/tinydrm-helpers.h
> @@ -43,6 +43,7 @@ void tinydrm_swab16(u16 *dst, void *vaddr, struct drm_framebuffer *fb,
>  void tinydrm_xrgb8888_to_rgb565(u16 *dst, void *vaddr,
>  				struct drm_framebuffer *fb,
>  				struct drm_clip_rect *clip, bool swap);
> +int tinydrm_xrgb8888_to_gray8(u8 *dst, struct drm_framebuffer *fb);
>  
>  struct backlight_device *tinydrm_of_find_backlight(struct device *dev);
>  int tinydrm_enable_backlight(struct backlight_device *backlight);
> -- 
> 2.7.4
> 
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> dri-devel at lists.freedesktop.org
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch