Re: [PATCH] drm: Use horizontal and vertical chroma subsampling factor while calculating offsets in the physical address of framebuffer

[Liviu Dudau <liviu.dudau@arm.com>]

On Fri, Aug 17, 2018 at 06:33:04PM +0100, Ayan Kumar Halder wrote:
> For multi-planar formats, while calculating offsets in planes with index greater than 0
> (ie second plane, third plane, etc), one needs to divide (src_x * cpp) with horizontal
> chroma subsampling factor and (src_y * pitch) with vertical chroma subsampling factor.
> 
> The reason being that the planes contain subsampled (ie reduced) data (by a factor of 2) and thus the

drop the extraneous "the" at the end of the line.

> while calculating the byte position coresponding to the x and y co-ordinates, one needs to be

and drop the extraneous "be" at the end of this line.

> divide it with the sampling factor.
> 
> Signed-off-by: Ayan Kumar halder <ayan.halder@arm.com>

Otherwise, it looks good to me!

Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>

Best regards,
Liviu

> ---
>  drivers/gpu/drm/drm_fb_cma_helper.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_fb_cma_helper.c b/drivers/gpu/drm/drm_fb_cma_helper.c
> index b127061..47e0e2f 100644
> --- a/drivers/gpu/drm/drm_fb_cma_helper.c
> +++ b/drivers/gpu/drm/drm_fb_cma_helper.c
> @@ -86,14 +86,21 @@ dma_addr_t drm_fb_cma_get_gem_addr(struct drm_framebuffer *fb,
>  {
>  	struct drm_gem_cma_object *obj;
>  	dma_addr_t paddr;
> +	u8 h_div = 1, v_div = 1;
>  
>  	obj = drm_fb_cma_get_gem_obj(fb, plane);
>  	if (!obj)
>  		return 0;
>  
>  	paddr = obj->paddr + fb->offsets[plane];
> -	paddr += fb->format->cpp[plane] * (state->src_x >> 16);
> -	paddr += fb->pitches[plane] * (state->src_y >> 16);
> +
> +	if (plane > 0) {
> +		h_div = fb->format->hsub;
> +		v_div = fb->format->vsub;
> +	}
> +
> +	paddr += (fb->format->cpp[plane] * (state->src_x >> 16)) / h_div;
> +	paddr += (fb->pitches[plane] * (state->src_y >> 16)) / v_div;
>  
>  	return paddr;
>  }
> -- 
> 2.7.4
> 

-- 
====================
| I would like to |
| fix the world,  |
| but they're not |
| giving me the   |
 \ source code!  /
  ---------------
    ¯\_(ツ)_/¯