drm/msm/dsi/phy: Fix reading zero as PLL rates when unprepared

Hardware Programming Guide for DSI PHY says that PLL_SHUTDOWNB and
DIGTOP_PWRDN_B have to be asserted for any PLL register access.
Whenever dsi_pll_7nm_vco_recalc_rate() or dsi_pll_7nm_vco_set_rate()
were called on unprepared PLL, driver read values of zero leading to all
sort of further troubles, like failing to set pixel and byte clock
rates.

Asserting the PLL shutdown bit is done by dsi_pll_enable_pll_bias() (and
corresponding dsi_pll_disable_pll_bias()) which are called through the
code, including from PLL .prepare() and .unprepare() callbacks.

The .set_rate() and .recalc_rate() can be called almost anytime from
external users including times when PLL is or is not prepared, thus
driver should not interfere with the prepare status.

Implement simple reference counting for the PLL bias, so
set_rate/recalc_rate will not change the status of prepared PLL.

Issue of reading 0 in .recalc_rate() did not show up on existing
devices, but only after re-ordering the code for SM8750.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Patchwork: https://patchwork.freedesktop.org/patch/673416/
Link: https://lore.kernel.org/r/20250908094950.72877-2-krzysztof.kozlowski@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>

Author: krzk

drivers/gpu/drm/msm/dsi/phy/dsi_phy.h

@@ -109,6 +109,7 @@ struct msm_dsi_phy {
 	struct msm_dsi_dphy_timing timing;
 	const struct msm_dsi_phy_cfg *cfg;
 	void *tuning_cfg;
+	void *pll_data;
 
 	enum msm_dsi_phy_usecase usecase;
 	bool regulator_ldo_mode;

drivers/gpu/drm/msm/dsi/phy/dsi_phy_7nm.c

@@ -90,6 +90,13 @@ struct dsi_pll_7nm {
 	/* protects REG_DSI_7nm_PHY_CMN_CLK_CFG1 register */
 	spinlock_t pclk_mux_lock;
 
+	/*
+	 * protects REG_DSI_7nm_PHY_CMN_CTRL_0 register and pll_enable_cnt
+	 * member
+	 */
+	spinlock_t pll_enable_lock;
+	int pll_enable_cnt;
+
 	struct pll_7nm_cached_state cached_state;
 
 	struct dsi_pll_7nm *slave;
@@ -103,6 +110,9 @@ struct dsi_pll_7nm {
  */
 static struct dsi_pll_7nm *pll_7nm_list[DSI_MAX];
 
+static void dsi_pll_enable_pll_bias(struct dsi_pll_7nm *pll);
+static void dsi_pll_disable_pll_bias(struct dsi_pll_7nm *pll);
+
 static void dsi_pll_setup_config(struct dsi_pll_config *config)
 {
 	config->ssc_freq = 31500;
@@ -340,6 +350,7 @@ static int dsi_pll_7nm_vco_set_rate(struct clk_hw *hw, unsigned long rate,
 	struct dsi_pll_7nm *pll_7nm = to_pll_7nm(hw);
 	struct dsi_pll_config config;
 
+	dsi_pll_enable_pll_bias(pll_7nm);
 	DBG("DSI PLL%d rate=%lu, parent's=%lu", pll_7nm->phy->id, rate,
 	    parent_rate);
 
@@ -357,6 +368,7 @@ static int dsi_pll_7nm_vco_set_rate(struct clk_hw *hw, unsigned long rate,
 
 	dsi_pll_ssc_commit(pll_7nm, &config);
 
+	dsi_pll_disable_pll_bias(pll_7nm);
 	/* flush, ensure all register writes are done*/
 	wmb();
 
@@ -385,24 +397,47 @@ static int dsi_pll_7nm_lock_status(struct dsi_pll_7nm *pll)
 
 static void dsi_pll_disable_pll_bias(struct dsi_pll_7nm *pll)
 {
+	unsigned long flags;
 	u32 data;
 
+	spin_lock_irqsave(&pll->pll_enable_lock, flags);
+	--pll->pll_enable_cnt;
+	if (pll->pll_enable_cnt < 0) {
+		spin_unlock_irqrestore(&pll->pll_enable_lock, flags);
+		DRM_DEV_ERROR_RATELIMITED(&pll->phy->pdev->dev,
+					  "bug: imbalance in disabling PLL bias\n");
+		return;
+	} else if (pll->pll_enable_cnt > 0) {
+		spin_unlock_irqrestore(&pll->pll_enable_lock, flags);
+		return;
+	} /* else: == 0 */
+
 	data = readl(pll->phy->base + REG_DSI_7nm_PHY_CMN_CTRL_0);
 	data &= ~DSI_7nm_PHY_CMN_CTRL_0_PLL_SHUTDOWNB;
 	writel(0, pll->phy->pll_base + REG_DSI_7nm_PHY_PLL_SYSTEM_MUXES);
 	writel(data, pll->phy->base + REG_DSI_7nm_PHY_CMN_CTRL_0);
+	spin_unlock_irqrestore(&pll->pll_enable_lock, flags);
 	ndelay(250);
 }
 
 static void dsi_pll_enable_pll_bias(struct dsi_pll_7nm *pll)
 {
+	unsigned long flags;
 	u32 data;
 
+	spin_lock_irqsave(&pll->pll_enable_lock, flags);
+	if (pll->pll_enable_cnt++) {
+		spin_unlock_irqrestore(&pll->pll_enable_lock, flags);
+		WARN_ON(pll->pll_enable_cnt == INT_MAX);
+		return;
+	}
+
 	data = readl(pll->phy->base + REG_DSI_7nm_PHY_CMN_CTRL_0);
 	data |= DSI_7nm_PHY_CMN_CTRL_0_PLL_SHUTDOWNB;
 	writel(data, pll->phy->base + REG_DSI_7nm_PHY_CMN_CTRL_0);
 
 	writel(0xc0, pll->phy->pll_base + REG_DSI_7nm_PHY_PLL_SYSTEM_MUXES);
+	spin_unlock_irqrestore(&pll->pll_enable_lock, flags);
 	ndelay(250);
 }
 
@@ -543,6 +578,7 @@ static unsigned long dsi_pll_7nm_vco_recalc_rate(struct clk_hw *hw,
 	u32 dec;
 	u64 pll_freq, tmp64;
 
+	dsi_pll_enable_pll_bias(pll_7nm);
 	dec = readl(base + REG_DSI_7nm_PHY_PLL_DECIMAL_DIV_START_1);
 	dec &= 0xff;
 
@@ -567,6 +603,8 @@ static unsigned long dsi_pll_7nm_vco_recalc_rate(struct clk_hw *hw,
 	DBG("DSI PLL%d returning vco rate = %lu, dec = %x, frac = %x",
 	    pll_7nm->phy->id, (unsigned long)vco_rate, dec, frac);
 
+	dsi_pll_disable_pll_bias(pll_7nm);
+
 	return (unsigned long)vco_rate;
 }
 
@@ -600,6 +638,7 @@ static void dsi_7nm_pll_save_state(struct msm_dsi_phy *phy)
 	void __iomem *phy_base = pll_7nm->phy->base;
 	u32 cmn_clk_cfg0, cmn_clk_cfg1;
 
+	dsi_pll_enable_pll_bias(pll_7nm);
 	cached->pll_out_div = readl(pll_7nm->phy->pll_base +
 			REG_DSI_7nm_PHY_PLL_PLL_OUTDIV_RATE);
 	cached->pll_out_div &= 0x3;
@@ -611,6 +650,7 @@ static void dsi_7nm_pll_save_state(struct msm_dsi_phy *phy)
 	cmn_clk_cfg1 = readl(phy_base + REG_DSI_7nm_PHY_CMN_CLK_CFG1);
 	cached->pll_mux = FIELD_GET(DSI_7nm_PHY_CMN_CLK_CFG1_DSICLK_SEL__MASK, cmn_clk_cfg1);
 
+	dsi_pll_disable_pll_bias(pll_7nm);
 	DBG("DSI PLL%d outdiv %x bit_clk_div %x pix_clk_div %x pll_mux %x",
 	    pll_7nm->phy->id, cached->pll_out_div, cached->bit_clk_div,
 	    cached->pix_clk_div, cached->pll_mux);
@@ -833,8 +873,10 @@ static int dsi_pll_7nm_init(struct msm_dsi_phy *phy)
 
 	spin_lock_init(&pll_7nm->postdiv_lock);
 	spin_lock_init(&pll_7nm->pclk_mux_lock);
+	spin_lock_init(&pll_7nm->pll_enable_lock);
 
 	pll_7nm->phy = phy;
+	phy->pll_data = pll_7nm;
 
 	ret = pll_7nm_register(pll_7nm, phy->provided_clocks->hws);
 	if (ret) {
@@ -923,8 +965,10 @@ static int dsi_7nm_phy_enable(struct msm_dsi_phy *phy,
 	u32 const delay_us = 5;
 	u32 const timeout_us = 1000;
 	struct msm_dsi_dphy_timing *timing = &phy->timing;
+	struct dsi_pll_7nm *pll = phy->pll_data;
 	void __iomem *base = phy->base;
 	bool less_than_1500_mhz;
+	unsigned long flags;
 	u32 vreg_ctrl_0, vreg_ctrl_1, lane_ctrl0;
 	u32 glbl_pemph_ctrl_0;
 	u32 glbl_str_swi_cal_sel_ctrl, glbl_hstx_str_ctrl_0;
@@ -1046,10 +1090,13 @@ static int dsi_7nm_phy_enable(struct msm_dsi_phy *phy,
 		glbl_rescode_bot_ctrl = 0x3c;
 	}
 
+	spin_lock_irqsave(&pll->pll_enable_lock, flags);
+	pll->pll_enable_cnt = 1;
 	/* de-assert digital and pll power down */
 	data = DSI_7nm_PHY_CMN_CTRL_0_DIGTOP_PWRDN_B |
 	       DSI_7nm_PHY_CMN_CTRL_0_PLL_SHUTDOWNB;
 	writel(data, base + REG_DSI_7nm_PHY_CMN_CTRL_0);
+	spin_unlock_irqrestore(&pll->pll_enable_lock, flags);
 
 	/* Assert PLL core reset */
 	writel(0x00, base + REG_DSI_7nm_PHY_CMN_PLL_CNTRL);
@@ -1162,7 +1209,9 @@ static bool dsi_7nm_set_continuous_clock(struct msm_dsi_phy *phy, bool enable)
 
 static void dsi_7nm_phy_disable(struct msm_dsi_phy *phy)
 {
+	struct dsi_pll_7nm *pll = phy->pll_data;
 	void __iomem *base = phy->base;
+	unsigned long flags;
 	u32 data;
 
 	DBG("");
@@ -1189,8 +1238,12 @@ static void dsi_7nm_phy_disable(struct msm_dsi_phy *phy)
 	writel(data, base + REG_DSI_7nm_PHY_CMN_CTRL_0);
 	writel(0, base + REG_DSI_7nm_PHY_CMN_LANE_CTRL0);
 
+	spin_lock_irqsave(&pll->pll_enable_lock, flags);
+	pll->pll_enable_cnt = 0;
 	/* Turn off all PHY blocks */
 	writel(0x00, base + REG_DSI_7nm_PHY_CMN_CTRL_0);
+	spin_unlock_irqrestore(&pll->pll_enable_lock, flags);
+
 	/* make sure phy is turned off */
 	wmb();