drm/msm/dsi: Account for DSC's bits_per_pixel having 4 fractional bits

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: b9080324 ("drm/msm/dsi: add support for dsc data")
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Marijn Suijten <marijn.suijten@somainline.org>
Patchwork: https://patchwork.freedesktop.org/patch/508938/
Link: https://lore.kernel.org/r/20221026182824.876933-8-marijn.suijten@somainline.orgSigned-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

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
@@ -1748,9 +1751,15 @@ 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;
+	}
 
 	dsc->rc_model_size = 8192;
 	dsc->first_line_bpg_offset = 12;
@@ -1772,7 +1781,7 @@ static int dsi_populate_dsc_params(struct drm_dsc_config *dsc)
 	}
 
 	dsc->initial_offset = 6144;		/* Not bpp 12 */
-	if (dsc->bits_per_pixel != 8)
+	if (bpp != 8)
 		dsc->initial_offset = 2048;	/* bpp = 12 */
 
 	if (dsc->bits_per_component <= 10)