drm/vc4: Turn the V3D clock on at runtime.

For the Raspberry Pi's bindings, the power domain also implicitly
turns on the clock and deasserts reset, but for the new Cygnus port we
start representing the clock in the devicetree.

v2: Document the clock-names property, check for -ENOENT for no clock
    in DT.
v3: Drop NULL checks around clk calls which embed NULL checks.
v4: Drop clk-names (feedback by Rob Herring)
Signed-off-by: Eric Anholt <eric@anholt.net>
Acked-by: Rob Herring <robh@kernel.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20170428224223.21904-1-eric@anholt.net

Documentation/devicetree/bindings/display/brcm,bcm-vc4.txt

@@ -59,6 +59,9 @@ Required properties for V3D:
 - interrupts:	The interrupt number
 		  See bindings/interrupt-controller/brcm,bcm2835-armctrl-ic.txt
 
+Optional properties for V3D:
+- clocks:	The clock the unit runs on
+
 Required properties for DSI:
 - compatible:	Should be "brcm,bcm2835-dsi0" or "brcm,bcm2835-dsi1"
 - reg:		Physical base address and length of the DSI block's registers

drivers/gpu/drm/vc4/vc4_drv.h

@@ -200,6 +200,7 @@ struct vc4_v3d {
 	struct vc4_dev *vc4;
 	struct platform_device *pdev;
 	void __iomem *regs;
+	struct clk *clk;
 };
 
 struct vc4_hvs {

drivers/gpu/drm/vc4/vc4_v3d.c

@@ -16,6 +16,7 @@
  * this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
+#include "linux/clk.h"
 #include "linux/component.h"
 #include "linux/pm_runtime.h"
 #include "vc4_drv.h"
@@ -305,6 +306,8 @@ static int vc4_v3d_runtime_suspend(struct device *dev)
 	drm_gem_object_put_unlocked(&vc4->bin_bo->base.base);
 	vc4->bin_bo = NULL;
 
+	clk_disable_unprepare(v3d->clk);
+
 	return 0;
 }
 
@@ -318,6 +321,10 @@ static int vc4_v3d_runtime_resume(struct device *dev)
 	if (ret)
 		return ret;
 
+	ret = clk_prepare_enable(v3d->clk);
+	if (ret != 0)
+		return ret;
+
 	vc4_v3d_init_hw(vc4->dev);
 	vc4_irq_postinstall(vc4->dev);
 
@@ -348,15 +355,37 @@ static int vc4_v3d_bind(struct device *dev, struct device *master, void *data)
 	vc4->v3d = v3d;
 	v3d->vc4 = vc4;
 
+	v3d->clk = devm_clk_get(dev, NULL);
+	if (IS_ERR(v3d->clk)) {
+		int ret = PTR_ERR(v3d->clk);
+
+		if (ret == -ENOENT) {
+			/* bcm2835 didn't have a clock reference in the DT. */
+			ret = 0;
+			v3d->clk = NULL;
+		} else {
+			if (ret != -EPROBE_DEFER)
+				dev_err(dev, "Failed to get V3D clock: %d\n",
+					ret);
+			return ret;
+		}
+	}
+
 	if (V3D_READ(V3D_IDENT0) != V3D_EXPECTED_IDENT0) {
 		DRM_ERROR("V3D_IDENT0 read 0x%08x instead of 0x%08x\n",
 			  V3D_READ(V3D_IDENT0), V3D_EXPECTED_IDENT0);
 		return -EINVAL;
 	}
 
+	ret = clk_prepare_enable(v3d->clk);
+	if (ret != 0)
+		return ret;
+
 	ret = vc4_allocate_bin_bo(drm);
-	if (ret)
+	if (ret) {
+		clk_disable_unprepare(v3d->clk);
 		return ret;
+	}
 
 	/* Reset the binner overflow address/size at setup, to be sure
 	 * we don't reuse an old one.