drm/tilcdc: rewrite pixel clock calculation

Updating the tilcdc DRM driver code to calculate the LCD controller
pixel clock more accurately. Based on a suggested implementation by
Tomi Valkeinen.

The current code does not work correctly and produces wrong results
with many requested clock rates. It also oddly uses two different
clocks, a display pll clock and a divider clock (child of display
pll), instead of just using the clock coming to the lcdc.

This patch removes the use of the display pll clock, and rewrites the
code to calculate the clock rates. The idea is simply to request a
clock rate of pixelclock*2, as the LCD controller has an internal
divider which we set to 2.

Signed-off-by: Darren Etheridge <detheridge@ti.com>
[Rewrapped description]
Signed-off-by: Jyri Sarha <jsarha@ti.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

drivers/gpu/drm/tilcdc/tilcdc_crtc.c

@@ -573,7 +573,8 @@ void tilcdc_crtc_update_clk(struct drm_crtc *crtc)
 	struct drm_device *dev = crtc->dev;
 	struct tilcdc_drm_private *priv = dev->dev_private;
 	int dpms = tilcdc_crtc->dpms;
-	unsigned int lcd_clk, div;
+	unsigned long lcd_clk;
+	const unsigned clkdiv = 2; /* using a fixed divider of 2 */
 	int ret;
 
 	pm_runtime_get_sync(dev->dev);
@@ -581,22 +582,21 @@ void tilcdc_crtc_update_clk(struct drm_crtc *crtc)
 	if (dpms == DRM_MODE_DPMS_ON)
 		tilcdc_crtc_dpms(crtc, DRM_MODE_DPMS_OFF);
 
-	/* in raster mode, minimum divisor is 2: */
-	ret = clk_set_rate(priv->disp_clk, crtc->mode.clock * 1000 * 2);
-	if (ret) {
+	/* mode.clock is in KHz, set_rate wants parameter in Hz */
+	ret = clk_set_rate(priv->clk, crtc->mode.clock * 1000 * clkdiv);
+	if (ret < 0) {
 		dev_err(dev->dev, "failed to set display clock rate to: %d\n",
 				crtc->mode.clock);
 		goto out;
 	}
 
 	lcd_clk = clk_get_rate(priv->clk);
-	div = lcd_clk / (crtc->mode.clock * 1000);
 
-	DBG("lcd_clk=%u, mode clock=%d, div=%u", lcd_clk, crtc->mode.clock, div);
-	DBG("fck=%lu, dpll_disp_ck=%lu", clk_get_rate(priv->clk), clk_get_rate(priv->disp_clk));
+	DBG("lcd_clk=%lu, mode clock=%d, div=%u",
+		lcd_clk, crtc->mode.clock, clkdiv);
 
 	/* Configure the LCD clock divisor. */
-	tilcdc_write(dev, LCDC_CTRL_REG, LCDC_CLK_DIVISOR(div) |
+	tilcdc_write(dev, LCDC_CTRL_REG, LCDC_CLK_DIVISOR(clkdiv) |
 			LCDC_RASTER_MODE);
 
 	if (priv->rev == 2)

drivers/gpu/drm/tilcdc/tilcdc_drv.c

@@ -192,13 +192,6 @@ static int tilcdc_load(struct drm_device *dev, unsigned long flags)
 		goto fail_iounmap;
 	}
 
-	priv->disp_clk = clk_get(dev->dev, "dpll_disp_ck");
-	if (IS_ERR(priv->clk)) {
-		dev_err(dev->dev, "failed to get display clock\n");
-		ret = -ENODEV;
-		goto fail_put_clk;
-	}
-
 #ifdef CONFIG_CPU_FREQ
 	priv->lcd_fck_rate = clk_get_rate(priv->clk);
 	priv->freq_transition.notifier_call = cpufreq_transition;
@@ -206,7 +199,7 @@ static int tilcdc_load(struct drm_device *dev, unsigned long flags)
 			CPUFREQ_TRANSITION_NOTIFIER);
 	if (ret) {
 		dev_err(dev->dev, "failed to register cpufreq notifier\n");
-		goto fail_put_disp_clk;
+		goto fail_put_clk;
 	}
 #endif
 
@@ -330,8 +323,6 @@ fail_cpufreq_unregister:
 #ifdef CONFIG_CPU_FREQ
 	cpufreq_unregister_notifier(&priv->freq_transition,
 			CPUFREQ_TRANSITION_NOTIFIER);
-fail_put_disp_clk:
-	clk_put(priv->disp_clk);
 #endif
 
 fail_put_clk:

drivers/gpu/drm/tilcdc/tilcdc_drv.h

@@ -49,7 +49,6 @@
 struct tilcdc_drm_private {
 	void __iomem *mmio;
 
-	struct clk *disp_clk;    /* display dpll */
 	struct clk *clk;         /* functional clock */
 	int rev;                 /* IP revision */