drm/msm/dsi/dsi_phy_10nm: Fix missing initial VCO rate

Driver unconditionally saves current state on first init in
dsi_pll_10nm_init(), but does not save the VCO rate, only some of the
divider registers.  The state is then restored during probe/enable via
msm_dsi_phy_enable() -> msm_dsi_phy_pll_restore_state() ->
dsi_10nm_pll_restore_state().

Restoring calls dsi_pll_10nm_vco_set_rate() with
pll_10nm->vco_current_rate=0, which basically overwrites existing rate of
VCO and messes with clock hierarchy, by setting frequency to 0 to clock
tree.  This makes anyway little sense - VCO rate was not saved, so
should not be restored.

If PLL was not configured configure it to minimum rate to avoid glitches
and configuring entire in clock hierarchy to 0 Hz.

Suggested-by: Dmitry Baryshkov <[email protected]>
Link: https://lore.kernel.org/r/sz4kbwy5nwsebgf64ia7uq4ee7wbsa5uy3xmlqwcstsbntzcov@ew3dcyjdzmi2/
Signed-off-by: Krzysztof Kozlowski <[email protected]>
Fixes: a4ccc37 ("drm/msm/dsi_pll_10nm: restore VCO rate during
Reviewed-by: Dmitry Baryshkov <[email protected]>
Patchwork: https://patchwork.freedesktop.org/patch/654796/
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Dmitry Baryshkov <[email protected]>

Author: krzk

drivers/gpu/drm/msm/dsi/phy/dsi_phy_10nm.c

@@ -704,6 +704,13 @@ static int dsi_pll_10nm_init(struct msm_dsi_phy *phy)
 	/* TODO: Remove this when we have proper display handover support */
 	msm_dsi_phy_pll_save_state(phy);
 
+	/*
+	 * Store also proper vco_current_rate, because its value will be used in
+	 * dsi_10nm_pll_restore_state().
+	 */
+	if (!dsi_pll_10nm_vco_recalc_rate(&pll_10nm->clk_hw, VCO_REF_CLK_RATE))
+		pll_10nm->vco_current_rate = pll_10nm->phy->cfg->min_pll_rate;
+
 	return 0;
 }