Re: [PATCH v3 08/10] drm/msm/dsi: Account for DSC's bits_per_pixel having 4 fractional bits

[Abhinav Kumar]

On 10/9/2022 11:53 AM, Marijn Suijten wrote:
> drm_dsc_config's bits_per_pixel field holds a fractional value with 4
> bits, which all panel drivers should adhere to for
> drm_dsc_pps_payload_pack() to generate a valid payload.  All code in the
> DSI driver here seems to assume that this field doesn't contain any
> fractional bits, hence resulting in the wrong values being computed.
> Since none of the calculations leave any room for fractional bits or
> seem to indicate any possible area of support, disallow such values
> altogether.  calculate_rc_params() in intel_vdsc.c performs an identical
> bitshift to get at this integer value.
>
> Fixes: b9080324d6ca ("drm/msm/dsi: add support for dsc data")
> Signed-off-by: Marijn Suijten <marijn.suijten@xxxxxxxxxxxxxx>
Reviewed-by: Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx>
> ---
>   drivers/gpu/drm/msm/dsi/dsi_host.c | 19 ++++++++++++++-----
>   1 file changed, 14 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
> index 7e6b7e506ae8..46032c576a59 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
> @@ -34,7 +34,7 @@
>   
>   #define DSI_RESET_TOGGLE_DELAY_MS 20
>   
> -static int dsi_populate_dsc_params(struct drm_dsc_config *dsc);
> +static int dsi_populate_dsc_params(struct msm_dsi_host *msm_host, struct drm_dsc_config *dsc);
>   
>   static int dsi_get_version(const void __iomem *base, u32 *major, u32 *minor)
>   {
> @@ -909,6 +909,7 @@ static void dsi_timing_setup(struct msm_dsi_host *msm_host, bool is_bonded_dsi)
>   	u32 va_end = va_start + mode->vdisplay;
>   	u32 hdisplay = mode->hdisplay;
>   	u32 wc;
> +	int ret;
>   
>   	DBG("");
>   
> @@ -944,7 +945,9 @@ static void dsi_timing_setup(struct msm_dsi_host *msm_host, bool is_bonded_dsi)
>   		/* we do the calculations for dsc parameters here so that
>   		 * panel can use these parameters
>   		 */
> -		dsi_populate_dsc_params(dsc);
> +		ret = dsi_populate_dsc_params(msm_host, dsc);
> +		if (ret)
> +			return;
>   
>   		/* Divide the display by 3 but keep back/font porch and
>   		 * pulse width same
> @@ -1770,9 +1773,15 @@ static char bpg_offset[DSC_NUM_BUF_RANGES] = {
>   	2, 0, 0, -2, -4, -6, -8, -8, -8, -10, -10, -12, -12, -12, -12
>   };
>   
> -static int dsi_populate_dsc_params(struct drm_dsc_config *dsc)
> +static int dsi_populate_dsc_params(struct msm_dsi_host *msm_host, struct drm_dsc_config *dsc)
>   {
>   	int i;
> +	u16 bpp = dsc->bits_per_pixel >> 4;
> +
> +	if (dsc->bits_per_pixel & 0xf) {
> +		DRM_DEV_ERROR(&msm_host->pdev->dev, "DSI does not support fractional bits_per_pixel\n");
> +		return -EINVAL;
> +	}
>   
>   	if (dsc->bits_per_component != 8) {
>   		DRM_DEV_ERROR(&msm_host->pdev->dev, "DSI does not support bits_per_component != 8 yet\n");
> @@ -1798,8 +1807,8 @@ static int dsi_populate_dsc_params(struct drm_dsc_config *dsc)
>   		dsc->rc_range_params[i].range_bpg_offset = bpg_offset[i];
>   	}
>   
> -	dsc->initial_offset = 6144; /* Not bpp 12 */
> -	if (dsc->bits_per_pixel != 8)
> +	dsc->initial_offset = 6144;		/* Not bpp 12 */
> +	if (bpp != 8)
>   		dsc->initial_offset = 2048;	/* bpp = 12 */
>   
>   	if (dsc->bits_per_component <= 10)