drm/tegra: dc: Support OPP and SoC core voltage scaling

Add OPP and SoC core voltage scaling support to the display controller
driver. This is required for enabling system-wide DVFS on pre-Tegra186
SoCs.
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Tested-by: Peter Geis <pgwipeout@gmail.com> # Ouya T30
Tested-by: Paul Fertser <fercerpav@gmail.com> # PAZ00 T20
Tested-by: Nicolas Chauvet <kwizart@gmail.com> # PAZ00 T20 and TK1 T124
Tested-by: Matt Merhar <mattmerhar@protonmail.com> # Ouya T30
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>

drivers/gpu/drm/tegra/dc.c

@@ -11,9 +11,12 @@
 #include <linux/interconnect.h>
 #include <linux/module.h>
 #include <linux/of_device.h>
+#include <linux/pm_domain.h>
+#include <linux/pm_opp.h>
 #include <linux/pm_runtime.h>
 #include <linux/reset.h>
 
+#include <soc/tegra/common.h>
 #include <soc/tegra/pmc.h>
 
 #include <drm/drm_atomic.h>
@@ -1834,6 +1837,52 @@ int tegra_dc_state_setup_clock(struct tegra_dc *dc,
 	return 0;
 }
 
+static void tegra_dc_update_voltage_state(struct tegra_dc *dc,
+					  struct tegra_dc_state *state)
+{
+	unsigned long rate, pstate;
+	struct dev_pm_opp *opp;
+	int err;
+
+	if (!dc->has_opp_table)
+		return;
+
+	/* calculate actual pixel clock rate which depends on internal divider */
+	rate = DIV_ROUND_UP(clk_get_rate(dc->clk) * 2, state->div + 2);
+
+	/* find suitable OPP for the rate */
+	opp = dev_pm_opp_find_freq_ceil(dc->dev, &rate);
+
+	/*
+	 * Very high resolution modes may results in a clock rate that is
+	 * above the characterized maximum. In this case it's okay to fall
+	 * back to the characterized maximum.
+	 */
+	if (opp == ERR_PTR(-ERANGE))
+		opp = dev_pm_opp_find_freq_floor(dc->dev, &rate);
+
+	if (IS_ERR(opp)) {
+		dev_err(dc->dev, "failed to find OPP for %luHz: %pe\n",
+			rate, opp);
+		return;
+	}
+
+	pstate = dev_pm_opp_get_required_pstate(opp, 0);
+	dev_pm_opp_put(opp);
+
+	/*
+	 * The minimum core voltage depends on the pixel clock rate (which
+	 * depends on internal clock divider of the CRTC) and not on the
+	 * rate of the display controller clock. This is why we're not using
+	 * dev_pm_opp_set_rate() API and instead controlling the power domain
+	 * directly.
+	 */
+	err = dev_pm_genpd_set_performance_state(dc->dev, pstate);
+	if (err)
+		dev_err(dc->dev, "failed to set power domain state to %lu: %d\n",
+			pstate, err);
+}
+
 static void tegra_dc_set_clock_rate(struct tegra_dc *dc,
 				    struct tegra_dc_state *state)
 {
@@ -1867,6 +1916,8 @@ static void tegra_dc_set_clock_rate(struct tegra_dc *dc,
 	DRM_DEBUG_KMS("rate: %lu, div: %u\n", clk_get_rate(dc->clk),
 		      state->div);
 	DRM_DEBUG_KMS("pclk: %lu\n", state->pclk);
+
+	tegra_dc_update_voltage_state(dc, state);
 }
 
 static void tegra_dc_stop(struct tegra_dc *dc)
@@ -2057,6 +2108,13 @@ static void tegra_crtc_atomic_disable(struct drm_crtc *crtc,
 	err = host1x_client_suspend(&dc->client);
 	if (err < 0)
 		dev_err(dc->dev, "failed to suspend: %d\n", err);
+
+	if (dc->has_opp_table) {
+		err = dev_pm_genpd_set_performance_state(dc->dev, 0);
+		if (err)
+			dev_err(dc->dev,
+				"failed to clear power domain state: %d\n", err);
+	}
 }
 
 static void tegra_crtc_atomic_enable(struct drm_crtc *crtc,
@@ -3058,6 +3116,23 @@ static int tegra_dc_couple(struct tegra_dc *dc)
 	return 0;
 }
 
+static int tegra_dc_init_opp_table(struct tegra_dc *dc)
+{
+	struct tegra_core_opp_params opp_params = {};
+	int err;
+
+	err = devm_tegra_core_dev_init_opp_table(dc->dev, &opp_params);
+	if (err && err != -ENODEV)
+		return err;
+
+	if (err)
+		dc->has_opp_table = false;
+	else
+		dc->has_opp_table = true;
+
+	return 0;
+}
+
 static int tegra_dc_probe(struct platform_device *pdev)
 {
 	u64 dma_mask = dma_get_mask(pdev->dev.parent);
@@ -3123,6 +3198,10 @@ static int tegra_dc_probe(struct platform_device *pdev)
 		tegra_powergate_power_off(dc->powergate);
 	}
 
+	err = tegra_dc_init_opp_table(dc);
+	if (err < 0)
+		return err;
+
 	dc->regs = devm_platform_ioremap_resource(pdev, 0);
 	if (IS_ERR(dc->regs))
 		return PTR_ERR(dc->regs);

drivers/gpu/drm/tegra/dc.h

@@ -101,6 +101,8 @@ struct tegra_dc {
 	struct drm_info_list *debugfs_files;
 
 	const struct tegra_dc_soc_info *soc;
+
+	bool has_opp_table;
 };
 
 static inline struct tegra_dc *