drm/msm/dsi: properly handle the case of empty OPP table in dsi_mgr_bridge_mode_valid

It was left unnoticed during the review that even if there is no OPP
table in device tree, one will be created by a call to the function
devm_pm_opp_set_clkname(). This leads to dsi_mgr_bridge_mode_valid()
rejecting all modes if DT contains no OPP table for the DSI host.

Rework dsi_mgr_bridge_mode_valid() to handle this case by actually
checking that the table is populated with frequency entries before
returning an error.

Fixes: 8328041b8c82 ("drm/msm/dsi: implement opp table based check for dsi_mgr_bridge_mode_valid()")
Signed-off-by: Dmitry Baryshkov <[e-mail]>
Reviewed-by: Abhinav Kumar <[e-mail]>
Patchwork: https://patchwork.freedesktop.org/patch/520076/
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dmitry Baryshkov <[e-mail]>

drivers/gpu/drm/msm/dsi/dsi_manager.c

···
 
 	byte_clk_rate = dsi_byte_clk_get_rate(host, IS_BONDED_DSI(), mode);
 
-	/*
-	 * fail all errors except -ENODEV as that could mean that opp
-	 * table is not yet implemented
-	 */
 	opp = dev_pm_opp_find_freq_ceil(&pdev->dev, &byte_clk_rate);
-	if (IS_ERR(opp)) {
-		if (PTR_ERR(opp) == -ERANGE)
-			return MODE_CLOCK_RANGE;
-		else if (PTR_ERR(opp) != -ENODEV)
-			return MODE_ERROR;
-	} else {
+	if (!IS_ERR(opp)) {
 		dev_pm_opp_put(opp);
+	} else if (PTR_ERR(opp) == -ERANGE) {
+		/*
+		 * An empty table is created by devm_pm_opp_set_clkname() even
+		 * if there is none. Thus find_freq_ceil will still return
+		 * -ERANGE in such case.
+		 */
+		if (dev_pm_opp_get_opp_count(&pdev->dev) != 0)
+			return MODE_CLOCK_RANGE;
+	} else {
+			return MODE_ERROR;
 	}
 
 	return msm_dsi_host_check_dsc(host, mode);