[PATCH 1/4 v2] drm/mcde: Improve pixel fetcher FIFO depth setting

[Daniel Vetter]

On Sun, Aug 09, 2020 at 12:31:19AM +0200, Linus Walleij wrote:
> The pixel fetcher FIFO depth was just hardcoded to 48
> which works fine as long as the framebuffer is 32BPP
> and the DSI output is RGB888.
> 
> We will need more elaborate handling for some buffer
> formats and displays, so start to improve this function
> by setting reasonable defaults for 32, 24 and 16 BPP
> framebuffers.
> 
> Cc: newbytee at protonmail.com
> Cc: Stephan Gerhold <stephan at gerhold.net>
> Signed-off-by: Linus Walleij <linus.walleij at linaro.org>
> ---
>  drivers/gpu/drm/mcde/mcde_display.c | 34 +++++++++++++++++++++++++----
>  1 file changed, 30 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/mcde/mcde_display.c b/drivers/gpu/drm/mcde/mcde_display.c
> index cac660ac8803..cbc7c0c4955a 100644
> --- a/drivers/gpu/drm/mcde/mcde_display.c
> +++ b/drivers/gpu/drm/mcde/mcde_display.c
> @@ -333,7 +333,7 @@ static void mcde_configure_overlay(struct mcde *mcde, enum mcde_overlay ovl,
>  				   enum mcde_extsrc src,
>  				   enum mcde_channel ch,
>  				   const struct drm_display_mode *mode,
> -				   u32 format)
> +				   u32 format, int cpp)

Note that format->cpp is a bit outdated, since it doesn't work for planar
stuff. But I guess not a problem for you (for now at least). Blocky
formats like yuv don't set format->cpp, or at least not in the way you'd
expect.

Anyway now idea on the hw, but patch looks reasonable.

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

>  {
>  	u32 val;
>  	u32 conf1;
> @@ -342,6 +342,7 @@ static void mcde_configure_overlay(struct mcde *mcde, enum mcde_overlay ovl,
>  	u32 ljinc;
>  	u32 cr;
>  	u32 comp;
> +	u32 pixel_fetcher_watermark;
>  
>  	switch (ovl) {
>  	case MCDE_OVERLAY_0:
> @@ -426,8 +427,33 @@ static void mcde_configure_overlay(struct mcde *mcde, enum mcde_overlay ovl,
>  			format);
>  		break;
>  	}
> -	/* The default watermark level for overlay 0 is 48 */
> -	val |= 48 << MCDE_OVLXCONF2_PIXELFETCHERWATERMARKLEVEL_SHIFT;
> +
> +	/*
> +	 * Pixel fetch watermark level is max 0x1FFF pixels.
> +	 * Two basic rules should be followed:
> +	 * 1. The value should be at least 256 bits.
> +	 * 2. The sum of all active overlays pixelfetch watermark level
> +	 *    multiplied with bits per pixel, should be lower than the
> +	 *    size of input_fifo_size in bits.
> +	 * 3. The value should be a multiple of a line (256 bits).
> +	 */
> +	switch (cpp) {
> +	case 2:
> +		pixel_fetcher_watermark = 128;
> +		break;
> +	case 3:
> +		pixel_fetcher_watermark = 96;
> +		break;
> +	case 4:
> +		pixel_fetcher_watermark = 48;
> +		break;
> +	default:
> +		pixel_fetcher_watermark = 48;
> +		break;
> +	}
> +	dev_dbg(mcde->dev, "pixel fetcher watermark level %d pixels\n",
> +		pixel_fetcher_watermark);
> +	val |= pixel_fetcher_watermark << MCDE_OVLXCONF2_PIXELFETCHERWATERMARKLEVEL_SHIFT;
>  	writel(val, mcde->regs + conf2);
>  
>  	/* Number of bytes to fetch per line */
> @@ -932,7 +958,7 @@ static void mcde_display_enable(struct drm_simple_display_pipe *pipe,
>  	 * channel 0
>  	 */
>  	mcde_configure_overlay(mcde, MCDE_OVERLAY_0, MCDE_EXTSRC_0,
> -			       MCDE_CHANNEL_0, mode, format);
> +			       MCDE_CHANNEL_0, mode, format, cpp);
>  
>  	/*
>  	 * Configure pixel-per-line and line-per-frame for channel 0 and then
> -- 
> 2.26.2
> 
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> dri-devel at lists.freedesktop.org
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch