simplefb: add clock handling code

This claims and enables clocks listed in the simple framebuffer dt node.
This is needed so that the display engine, in case the required clocks
are known by the kernel code and are described in the dt, will remain
properly enabled.

Signed-off-by: Luc Verhaegen <libv@skynet.be>
[hdegoede@redhat.com: Change clks from list to dynamic array]
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Reviewed-by: David Herrmann <dh.herrmann@gmail.com>
Acked-by: Grant Likely <grant.likely@linaro.org>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

drivers/video/fbdev/simplefb.c

@@ -26,6 +26,7 @@
 #include <linux/module.h>
 #include <linux/platform_data/simplefb.h>
 #include <linux/platform_device.h>
+#include <linux/clk-provider.h>
 
 static struct fb_fix_screeninfo simplefb_fix = {
 	.id		= "simple",
@@ -167,8 +168,105 @@ static int simplefb_parse_pd(struct platform_device *pdev,
 
 struct simplefb_par {
 	u32 palette[PSEUDO_PALETTE_SIZE];
+#ifdef CONFIG_OF
+	int clk_count;
+	struct clk **clks;
+#endif
 };
 
+#ifdef CONFIG_OF
+/*
+ * Clock handling code.
+ *
+ * Here we handle the clocks property of our "simple-framebuffer" dt node.
+ * This is necessary so that we can make sure that any clocks needed by
+ * the display engine that the bootloader set up for us (and for which it
+ * provided a simplefb dt node), stay up, for the life of the simplefb
+ * driver.
+ *
+ * When the driver unloads, we cleanly disable, and then release the clocks.
+ *
+ * We only complain about errors here, no action is taken as the most likely
+ * error can only happen due to a mismatch between the bootloader which set
+ * up simplefb, and the clock definitions in the device tree. Chances are
+ * that there are no adverse effects, and if there are, a clean teardown of
+ * the fb probe will not help us much either. So just complain and carry on,
+ * and hope that the user actually gets a working fb at the end of things.
+ */
+static int simplefb_clocks_init(struct simplefb_par *par,
+				struct platform_device *pdev)
+{
+	struct device_node *np = pdev->dev.of_node;
+	struct clk *clock;
+	int i, ret;
+
+	if (dev_get_platdata(&pdev->dev) || !np)
+		return 0;
+
+	par->clk_count = of_clk_get_parent_count(np);
+	if (par->clk_count <= 0)
+		return 0;
+
+	par->clks = kcalloc(par->clk_count, sizeof(struct clk *), GFP_KERNEL);
+	if (!par->clks)
+		return -ENOMEM;
+
+	for (i = 0; i < par->clk_count; i++) {
+		clock = of_clk_get(np, i);
+		if (IS_ERR(clock)) {
+			if (PTR_ERR(clock) == -EPROBE_DEFER) {
+				while (--i >= 0) {
+					if (par->clks[i])
+						clk_put(par->clks[i]);
+				}
+				kfree(par->clks);
+				return -EPROBE_DEFER;
+			}
+			dev_err(&pdev->dev, "%s: clock %d not found: %ld\n",
+				__func__, i, PTR_ERR(clock));
+			continue;
+		}
+		par->clks[i] = clock;
+	}
+
+	for (i = 0; i < par->clk_count; i++) {
+		if (par->clks[i]) {
+			ret = clk_prepare_enable(par->clks[i]);
+			if (ret) {
+				dev_err(&pdev->dev,
+					"%s: failed to enable clock %d: %d\n",
+					__func__, i, ret);
+				clk_put(par->clks[i]);
+				par->clks[i] = NULL;
+			}
+		}
+	}
+
+	return 0;
+}
+
+static void simplefb_clocks_destroy(struct simplefb_par *par)
+{
+	int i;
+
+	if (!par->clks)
+		return;
+
+	for (i = 0; i < par->clk_count; i++) {
+		if (par->clks[i]) {
+			clk_disable_unprepare(par->clks[i]);
+			clk_put(par->clks[i]);
+		}
+	}
+
+	kfree(par->clks);
+}
+#else
+static int simplefb_clocks_init(struct simplefb_par *par,
+	struct platform_device *pdev) { return 0; }
+static void simplefb_clocks_destroy(struct simplefb_par *par) { }
+#endif
+
 static int simplefb_probe(struct platform_device *pdev)
 {
 	int ret;
@@ -236,6 +334,10 @@ static int simplefb_probe(struct platform_device *pdev)
 	}
 	info->pseudo_palette = par->palette;
 
+	ret = simplefb_clocks_init(par, pdev);
+	if (ret < 0)
+		goto error_unmap;
+
 	dev_info(&pdev->dev, "framebuffer at 0x%lx, 0x%x bytes, mapped to 0x%p\n",
 			     info->fix.smem_start, info->fix.smem_len,
 			     info->screen_base);
@@ -247,13 +349,15 @@ static int simplefb_probe(struct platform_device *pdev)
 	ret = register_framebuffer(info);
 	if (ret < 0) {
 		dev_err(&pdev->dev, "Unable to register simplefb: %d\n", ret);
-		goto error_unmap;
+		goto error_clocks;
 	}
 
 	dev_info(&pdev->dev, "fb%d: simplefb registered!\n", info->node);
 
 	return 0;
 
+error_clocks:
+	simplefb_clocks_destroy(par);
 error_unmap:
 	iounmap(info->screen_base);
 error_fb_release:
@@ -264,8 +368,10 @@ static int simplefb_probe(struct platform_device *pdev)
 static int simplefb_remove(struct platform_device *pdev)
 {
 	struct fb_info *info = platform_get_drvdata(pdev);
+	struct simplefb_par *par = info->par;
 
 	unregister_framebuffer(info);
+	simplefb_clocks_destroy(par);
 	framebuffer_release(info);
 
 	return 0;