Re: [PATCH] drm/bridge: tc358767: fix max_tu_symbol value

[Jyri Sarha <jsarha@ti.com>]

On 24/09/2019 16:17, Tomi Valkeinen wrote:
> max_tu_symbol was programmed to TU_SIZE_RECOMMENDED - 1, which is not
> what the spec says. The spec says:
> 
> roundup ((input active video bandwidth in bytes/output active video
> bandwidth in bytes) * tu_size)
> 
> It is not quite clear what the above means, but calculating
> max_tu_symbol = (input Bps / output Bps) * tu_size seems to work and
> fixes the issues seen.
> 
> This fixes artifacts in some videomodes (e.g. 1024x768@60 on 2-lanes &
> 1.62Gbps was pretty bad for me).
> 
> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

I could reproduce the problem and see that the patch fixes it, so:

Tested-by: Jyri Sarha <jsarha@ti.com>


> ---
>  drivers/gpu/drm/bridge/tc358767.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/bridge/tc358767.c b/drivers/gpu/drm/bridge/tc358767.c
> index 13ade28a36a8..b6aa1bd47e1d 100644
> --- a/drivers/gpu/drm/bridge/tc358767.c
> +++ b/drivers/gpu/drm/bridge/tc358767.c
> @@ -677,6 +677,8 @@ static int tc_set_video_mode(struct tc_data *tc,
>  	int upper_margin = mode->vtotal - mode->vsync_end;
>  	int lower_margin = mode->vsync_start - mode->vdisplay;
>  	int vsync_len = mode->vsync_end - mode->vsync_start;
> +	u32 bits_per_pixel = 24;
> +	u32 in_bw, out_bw;
>  
>  	/*
>  	 * Recommended maximum number of symbols transferred in a transfer unit:
> @@ -684,7 +686,10 @@ static int tc_set_video_mode(struct tc_data *tc,
>  	 *              (output active video bandwidth in bytes))
>  	 * Must be less than tu_size.
>  	 */
> -	max_tu_symbol = TU_SIZE_RECOMMENDED - 1;
> +
> +	in_bw = mode->clock * bits_per_pixel / 8;
> +	out_bw = tc->link.base.num_lanes * tc->link.base.rate;
> +	max_tu_symbol = DIV_ROUND_UP(in_bw * TU_SIZE_RECOMMENDED, out_bw);
>  
>  	dev_dbg(tc->dev, "set mode %dx%d\n",
>  		mode->hdisplay, mode->vdisplay);
> 


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