drm/msm/dsi: Set PHY usescase (and mode) before registering DSI host

Ordering issues here cause an uninitialized (default STANDALONE)
usecase to be programmed (which appears to be a MUX) in some cases
when msm_dsi_host_register() is called, leading to the slave PLL in
bonded-DSI mode to source from a clock parent (dsi1vco) that is off.

This should seemingly not be a problem as the actual dispcc clocks from
DSI1 that are muxed in the clock tree of DSI0 are way further down, this
bit still seems to have an effect on them somehow and causes the right
side of the panel controlled by DSI1 to not function.

In an ideal world this code is refactored to no longer have such
error-prone calls "across subsystems", and instead model the "PLL src"
register field as a regular mux so that changing the clock parents
programmatically or in DTS via `assigned-clock-parents` has the
desired effect.
But for the avid reader, the clocks that we *are* muxing into DSI0's
tree are way further down, so if this bit turns out to be a simple mux
between dsiXvco and out_div, that shouldn't have any effect as this
whole tree is off anyway.

Fixes: 57bf433 ("drm/msm/dsi: Pass down use case to PHY")
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/637650/
Link: https://lore.kernel.org/r/20250217-drm-msm-initial-dualpipe-dsc-fixes-v3-2-913100d6103f@somainline.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

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

@@ -74,17 +74,35 @@ static int dsi_mgr_setup_components(int id)
 	int ret;
 
 	if (!IS_BONDED_DSI()) {
+		/*
+		 * Set the usecase before calling msm_dsi_host_register(), which would
+		 * already program the PLL source mux based on a default usecase.
+		 */
+		msm_dsi_phy_set_usecase(msm_dsi->phy, MSM_DSI_PHY_STANDALONE);
+		msm_dsi_host_set_phy_mode(msm_dsi->host, msm_dsi->phy);
+
 		ret = msm_dsi_host_register(msm_dsi->host);
 		if (ret)
 			return ret;
-
-		msm_dsi_phy_set_usecase(msm_dsi->phy, MSM_DSI_PHY_STANDALONE);
-		msm_dsi_host_set_phy_mode(msm_dsi->host, msm_dsi->phy);
 	} else if (other_dsi) {
 		struct msm_dsi *master_link_dsi = IS_MASTER_DSI_LINK(id) ?
 							msm_dsi : other_dsi;
 		struct msm_dsi *slave_link_dsi = IS_MASTER_DSI_LINK(id) ?
 							other_dsi : msm_dsi;
+
+		/*
+		 * PLL0 is to drive both DSI link clocks in bonded DSI mode.
+		 *
+		 * Set the usecase before calling msm_dsi_host_register(), which would
+		 * already program the PLL source mux based on a default usecase.
+		 */
+		msm_dsi_phy_set_usecase(clk_master_dsi->phy,
+					MSM_DSI_PHY_MASTER);
+		msm_dsi_phy_set_usecase(clk_slave_dsi->phy,
+					MSM_DSI_PHY_SLAVE);
+		msm_dsi_host_set_phy_mode(msm_dsi->host, msm_dsi->phy);
+		msm_dsi_host_set_phy_mode(other_dsi->host, other_dsi->phy);
+
 		/* Register slave host first, so that slave DSI device
 		 * has a chance to probe, and do not block the master
 		 * DSI device's probe.
@@ -98,14 +116,6 @@ static int dsi_mgr_setup_components(int id)
 		ret = msm_dsi_host_register(master_link_dsi->host);
 		if (ret)
 			return ret;
-
-		/* PLL0 is to drive both 2 DSI link clocks in bonded DSI mode. */
-		msm_dsi_phy_set_usecase(clk_master_dsi->phy,
-					MSM_DSI_PHY_MASTER);
-		msm_dsi_phy_set_usecase(clk_slave_dsi->phy,
-					MSM_DSI_PHY_SLAVE);
-		msm_dsi_host_set_phy_mode(msm_dsi->host, msm_dsi->phy);
-		msm_dsi_host_set_phy_mode(other_dsi->host, other_dsi->phy);
 	}
 
 	return 0;