Re: [PATCH v1] drm/mediatek: adjust rdma fifo threshold calculate formula

[CK Hu]

Hi, Yongqiang:

On Mon, 2021-04-12 at 15:25 +0800, Yongqiang Niu wrote:
> the orginal formula will caused rdma fifo threshold config overflow
> 
> Signed-off-by: Yongqiang Niu <yongqiang.niu@xxxxxxxxxxxx>
> ---
>  drivers/gpu/drm/mediatek/mtk_disp_rdma.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_disp_rdma.c b/drivers/gpu/drm/mediatek/mtk_disp_rdma.c
> index 728aaad..8c9371b 100644
> --- a/drivers/gpu/drm/mediatek/mtk_disp_rdma.c
> +++ b/drivers/gpu/drm/mediatek/mtk_disp_rdma.c
> @@ -167,7 +167,7 @@ void mtk_rdma_config(struct device *dev, unsigned int width,
>  	 * output threshold to 6 microseconds with 7/6 overhead to
>  	 * account for blanking, and with a pixel depth of 4 bytes:
>  	 */
> -	threshold = width * height * vrefresh * 4 * 7 / 1000000;
> +	threshold = rdma_fifo_size * 7 / 10;

It's better to set threshold by width and height, but it seems that no
one could come out a solution for all SoC. I could just accept this
solution, but I need some addition comment for this solution. How do you
decide 7/10? In the future, another may need to modify this value and he
need to know why you use 7/10. If you just choose it at random, just
tell us that you just randomly choose it.

Regards,
CK

>  	reg = RDMA_FIFO_UNDERFLOW_EN |
>  	      RDMA_FIFO_PSEUDO_SIZE(rdma_fifo_size) |
>  	      RDMA_OUTPUT_VALID_FIFO_THRESHOLD(threshold);