drm/msm/dsi: don't allow enabling 14nm VCO with unprogrammed rate

If the dispcc uses CLK_OPS_PARENT_ENABLE (e.g. on QCM2290), CCF can try
enabling VCO before the rate has been programmed. This can cause clock
lockups and/or other boot issues. Program the VCO to the minimal PLL
rate if the read rate is 0 Hz.

Cc: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reported-by: Vladimir Zapolskiy <vladimir.zapolskiy@linaro.org>
Reported-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Fixes: f079f6d9 ("drm/msm/dsi: Add PHY/PLL for 8x96")
Patchwork: https://patchwork.freedesktop.org/patch/534813/
Link: https://lore.kernel.org/r/20230501011257.3460103-1-dmitry.baryshkov@linaro.orgSigned-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

drivers/gpu/drm/msm/dsi/phy/dsi_phy_14nm.c

@@ -539,6 +539,9 @@ static int dsi_pll_14nm_vco_prepare(struct clk_hw *hw)
 	if (unlikely(pll_14nm->phy->pll_on))
 		return 0;
 
+	if (dsi_pll_14nm_vco_recalc_rate(hw, VCO_REF_CLK_RATE) == 0)
+		dsi_pll_14nm_vco_set_rate(hw, pll_14nm->phy->cfg->min_pll_rate, VCO_REF_CLK_RATE);
+
 	dsi_phy_write(base + REG_DSI_14nm_PHY_PLL_VREF_CFG1, 0x10);
 	dsi_phy_write(cmn_base + REG_DSI_14nm_PHY_CMN_PLL_CNTRL, 1);