video: add of helper for display timings/videomode

This adds support for reading display timings from DT into a struct
display_timings. The of_display_timing implementation supports multiple
subnodes. All children are read into an array, that can be queried.

If no native mode is specified, the first subnode will be used.

For cases where the graphics driver knows there can be only one
mode description or where the driver only supports one mode, a helper
function of_get_videomode is added, that gets a struct videomode from DT.

Signed-off-by: Steffen Trumtrar <[e-mail]>
Signed-off-by: Philipp Zabel <[e-mail]>
Acked-by: Stephen Warren <[e-mail]>
Reviewed-by: Thierry Reding <[e-mail]>
Acked-by: Thierry Reding <[e-mail]>
Tested-by: Thierry Reding <[e-mail]>
Tested-by: Philipp Zabel <[e-mail]>
Reviewed-by: Laurent Pinchart <[e-mail]>
Acked-by: Laurent Pinchart <[e-mail]>
Tested-by: Afzal Mohammed <[e-mail]>
Tested-by: Rob Clark <[e-mail]>
Tested-by: Leela Krishna Amudala <[e-mail]>

Documentation/devicetree/bindings/video/display-timing.txt

···
+display-timing bindings
+=======================
+
+display-timings node
+--------------------
+
+required properties:
+ - none
+
+optional properties:
+ - native-mode: The native mode for the display, in case multiple modes are
+		provided. When omitted, assume the first node is the native.
+
+timing subnode
+--------------
+
+required properties:
+ - hactive, vactive: display resolution
+ - hfront-porch, hback-porch, hsync-len: horizontal display timing parameters
+   in pixels
+   vfront-porch, vback-porch, vsync-len: vertical display timing parameters in
+   lines
+ - clock-frequency: display clock in Hz
+
+optional properties:
+ - hsync-active: hsync pulse is active low/high/ignored
+ - vsync-active: vsync pulse is active low/high/ignored
+ - de-active: data-enable pulse is active low/high/ignored
+ - pixelclk-active: with
+			- active high = drive pixel data on rising edge/
+					sample data on falling edge
+			- active low  = drive pixel data on falling edge/
+					sample data on rising edge
+			- ignored     = ignored
+ - interlaced (bool): boolean to enable interlaced mode
+ - doublescan (bool): boolean to enable doublescan mode
+
+All the optional properties that are not bool follow the following logic:
+    <1>: high active
+    <0>: low active
+    omitted: not used on hardware
+
+There are different ways of describing the capabilities of a display. The
+devicetree representation corresponds to the one commonly found in datasheets
+for displays. If a display supports multiple signal timings, the native-mode
+can be specified.
+
+The parameters are defined as:
+
+  +----------+-------------------------------------+----------+-------+
+  |          |        ↑                            |          |       |
+  |          |        |vback_porch                 |          |       |
+  |          |        ↓                            |          |       |
+  +----------#######################################----------+-------+
+  |          #        ↑                            #          |       |
+  |          #        |                            #          |       |
+  |  hback   #        |                            #  hfront  | hsync |
+  |   porch  #        |       hactive              #  porch   |  len  |
+  |<-------->#<-------+--------------------------->#<-------->|<----->|
+  |          #        |                            #          |       |
+  |          #        |vactive                     #          |       |
+  |          #        |                            #          |       |
+  |          #        ↓                            #          |       |
+  +----------#######################################----------+-------+
+  |          |        ↑                            |          |       |
+  |          |        |vfront_porch                |          |       |
+  |          |        ↓                            |          |       |
+  +----------+-------------------------------------+----------+-------+
+  |          |        ↑                            |          |       |
+  |          |        |vsync_len                   |          |       |
+  |          |        ↓                            |          |       |
+  +----------+-------------------------------------+----------+-------+
+
+Example:
+
+	display-timings {
+		native-mode = <&timing0>;
+		timing0: 1080p24 {
+			/* 1920x1080p24 */
+			clock-frequency = <52000000>;
+			hactive = <1920>;
+			vactive = <1080>;
+			hfront-porch = <25>;
+			hback-porch = <25>;
+			hsync-len = <25>;
+			vback-porch = <2>;
+			vfront-porch = <2>;
+			vsync-len = <2>;
+			hsync-active = <1>;
+		};
+	};
+
+Every required property also supports the use of ranges, so the commonly used
+datasheet description with minimum, typical and maximum values can be used.
+
+Example:
+
+	timing1: timing {
+		/* 1920x1080p24 */
+		clock-frequency = <148500000>;
+		hactive = <1920>;
+		vactive = <1080>;
+		hsync-len = <0 44 60>;
+		hfront-porch = <80 88 95>;
+		hback-porch = <100 148 160>;
+		vfront-porch = <0 4 6>;
+		vback-porch = <0 36 50>;
+		vsync-len = <0 5 6>;
+	};

drivers/video/Kconfig

···
 config VIDEOMODE
        bool
 
+config OF_DISPLAY_TIMING
+	bool "Enable device tree display timing support"
+	depends on OF
+	select DISPLAY_TIMING
+	help
+	  helper to parse display timings from the devicetree
+
+config OF_VIDEOMODE
+	bool "Enable device tree videomode support"
+	depends on OF
+	select VIDEOMODE
+	select OF_DISPLAY_TIMING
+	help
+	  helper to get videomodes from the devicetree
+
 menuconfig FB
 	tristate "Support for frame buffer devices"
 	---help---

drivers/video/Makefile

···
 #video output switch sysfs driver
 obj-$(CONFIG_VIDEO_OUTPUT_CONTROL) += output.o
 obj-$(CONFIG_DISPLAY_TIMING) += display_timing.o
+obj-$(CONFIG_OF_DISPLAY_TIMING) += of_display_timing.o
 obj-$(CONFIG_VIDEOMODE) += videomode.o
+obj-$(CONFIG_OF_VIDEOMODE) += of_videomode.o

drivers/video/of_display_timing.c

···
+/*
+ * OF helpers for parsing display timings
+ *
+ * Copyright (c) 2012 Steffen Trumtrar <[e-mail]>, Pengutronix
+ *
+ * based on of_videomode.c by Sascha Hauer <[e-mail]>
+ *
+ * This file is released under the GPLv2
+ */
+#include <linux/export.h>
+#include <linux/of.h>
+#include <linux/slab.h>
+#include <video/display_timing.h>
+#include <video/of_display_timing.h>
+
+/**
+ * parse_timing_property - parse timing_entry from device_node
+ * @np: device_node with the property
+ * @name: name of the property
+ * @result: will be set to the return value
+ *
+ * DESCRIPTION:
+ * Every display_timing can be specified with either just the typical value or
+ * a range consisting of min/typ/max. This function helps handling this
+ **/
+static int parse_timing_property(struct device_node *np, const char *name,
+			  struct timing_entry *result)
+{
+	struct property *prop;
+	int length, cells, ret;
+
+	prop = of_find_property(np, name, &length);
+	if (!prop) {
+		pr_err("%s: could not find property %s\n",
+			of_node_full_name(np), name);
+		return -EINVAL;
+	}
+
+	cells = length / sizeof(u32);
+	if (cells == 1) {
+		ret = of_property_read_u32(np, name, &result->typ);
+		result->min = result->typ;
+		result->max = result->typ;
+	} else if (cells == 3) {
+		ret = of_property_read_u32_array(np, name, &result->min, cells);
+	} else {
+		pr_err("%s: illegal timing specification in %s\n",
+			of_node_full_name(np), name);
+		return -EINVAL;
+	}
+
+	return ret;
+}
+
+/**
+ * of_get_display_timing - parse display_timing entry from device_node
+ * @np: device_node with the properties
+ **/
+static struct display_timing *of_get_display_timing(struct device_node *np)
+{
+	struct display_timing *dt;
+	u32 val = 0;
+	int ret = 0;
+
+	dt = kzalloc(sizeof(*dt), GFP_KERNEL);
+	if (!dt) {
+		pr_err("%s: could not allocate display_timing struct\n",
+			of_node_full_name(np));
+		return NULL;
+	}
+
+	ret |= parse_timing_property(np, "hback-porch", &dt->hback_porch);
+	ret |= parse_timing_property(np, "hfront-porch", &dt->hfront_porch);
+	ret |= parse_timing_property(np, "hactive", &dt->hactive);
+	ret |= parse_timing_property(np, "hsync-len", &dt->hsync_len);
+	ret |= parse_timing_property(np, "vback-porch", &dt->vback_porch);
+	ret |= parse_timing_property(np, "vfront-porch", &dt->vfront_porch);
+	ret |= parse_timing_property(np, "vactive", &dt->vactive);
+	ret |= parse_timing_property(np, "vsync-len", &dt->vsync_len);
+	ret |= parse_timing_property(np, "clock-frequency", &dt->pixelclock);
+
+	dt->dmt_flags = 0;
+	dt->data_flags = 0;
+	if (!of_property_read_u32(np, "vsync-active", &val))
+		dt->dmt_flags |= val ? VESA_DMT_VSYNC_HIGH :
+				VESA_DMT_VSYNC_LOW;
+	if (!of_property_read_u32(np, "hsync-active", &val))
+		dt->dmt_flags |= val ? VESA_DMT_HSYNC_HIGH :
+				VESA_DMT_HSYNC_LOW;
+	if (!of_property_read_u32(np, "de-active", &val))
+		dt->data_flags |= val ? DISPLAY_FLAGS_DE_HIGH :
+				DISPLAY_FLAGS_DE_LOW;
+	if (!of_property_read_u32(np, "pixelclk-active", &val))
+		dt->data_flags |= val ? DISPLAY_FLAGS_PIXDATA_POSEDGE :
+				DISPLAY_FLAGS_PIXDATA_NEGEDGE;
+
+	if (of_property_read_bool(np, "interlaced"))
+		dt->data_flags |= DISPLAY_FLAGS_INTERLACED;
+	if (of_property_read_bool(np, "doublescan"))
+		dt->data_flags |= DISPLAY_FLAGS_DOUBLESCAN;
+
+	if (ret) {
+		pr_err("%s: error reading timing properties\n",
+			of_node_full_name(np));
+		kfree(dt);
+		return NULL;
+	}
+
+	return dt;
+}
+
+/**
+ * of_get_display_timings - parse all display_timing entries from a device_node
+ * @np: device_node with the subnodes
+ **/
+struct display_timings *of_get_display_timings(struct device_node *np)
+{
+	struct device_node *timings_np;
+	struct device_node *entry;
+	struct device_node *native_mode;
+	struct display_timings *disp;
+
+	if (!np) {
+		pr_err("%s: no devicenode given\n", of_node_full_name(np));
+		return NULL;
+	}
+
+	timings_np = of_find_node_by_name(np, "display-timings");
+	if (!timings_np) {
+		pr_err("%s: could not find display-timings node\n",
+			of_node_full_name(np));
+		return NULL;
+	}
+
+	disp = kzalloc(sizeof(*disp), GFP_KERNEL);
+	if (!disp) {
+		pr_err("%s: could not allocate struct disp'\n",
+			of_node_full_name(np));
+		goto dispfail;
+	}
+
+	entry = of_parse_phandle(timings_np, "native-mode", 0);
+	/* assume first child as native mode if none provided */
+	if (!entry)
+		entry = of_get_next_child(np, NULL);
+	/* if there is no child, it is useless to go on */
+	if (!entry) {
+		pr_err("%s: no timing specifications given\n",
+			of_node_full_name(np));
+		goto entryfail;
+	}
+
+	pr_debug("%s: using %s as default timing\n",
+		of_node_full_name(np), entry->name);
+
+	native_mode = entry;
+
+	disp->num_timings = of_get_child_count(timings_np);
+	if (disp->num_timings == 0) {
+		/* should never happen, as entry was already found above */
+		pr_err("%s: no timings specified\n", of_node_full_name(np));
+		goto entryfail;
+	}
+
+	disp->timings = kzalloc(sizeof(struct display_timing *) *
+				disp->num_timings, GFP_KERNEL);
+	if (!disp->timings) {
+		pr_err("%s: could not allocate timings array\n",
+			of_node_full_name(np));
+		goto entryfail;
+	}
+
+	disp->num_timings = 0;
+	disp->native_mode = 0;
+
+	for_each_child_of_node(timings_np, entry) {
+		struct display_timing *dt;
+
+		dt = of_get_display_timing(entry);
+		if (!dt) {
+			/*
+			 * to not encourage wrong devicetrees, fail in case of
+			 * an error
+			 */
+			pr_err("%s: error in timing %d\n",
+				of_node_full_name(np), disp->num_timings + 1);
+			goto timingfail;
+		}
+
+		if (native_mode == entry)
+			disp->native_mode = disp->num_timings;
+
+		disp->timings[disp->num_timings] = dt;
+		disp->num_timings++;
+	}
+	of_node_put(timings_np);
+	/*
+	 * native_mode points to the device_node returned by of_parse_phandle
+	 * therefore call of_node_put on it
+	 */
+	of_node_put(native_mode);
+
+	pr_debug("%s: got %d timings. Using timing #%d as default\n",
+		of_node_full_name(np), disp->num_timings,
+		disp->native_mode + 1);
+
+	return disp;
+
+timingfail:
+	if (native_mode)
+		of_node_put(native_mode);
+	display_timings_release(disp);
+entryfail:
+	kfree(disp);
+dispfail:
+	of_node_put(timings_np);
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(of_get_display_timings);
+
+/**
+ * of_display_timings_exist - check if a display-timings node is provided
+ * @np: device_node with the timing
+ **/
+int of_display_timings_exist(struct device_node *np)
+{
+	struct device_node *timings_np;
+
+	if (!np)
+		return -EINVAL;
+
+	timings_np = of_parse_phandle(np, "display-timings", 0);
+	if (!timings_np)
+		return -EINVAL;
+
+	of_node_put(timings_np);
+	return 1;
+}
+EXPORT_SYMBOL_GPL(of_display_timings_exist);

drivers/video/of_videomode.c

···
+/*
+ * generic videomode helper
+ *
+ * Copyright (c) 2012 Steffen Trumtrar <[e-mail]>, Pengutronix
+ *
+ * This file is released under the GPLv2
+ */
+#include <linux/errno.h>
+#include <linux/export.h>
+#include <linux/of.h>
+#include <video/display_timing.h>
+#include <video/of_display_timing.h>
+#include <video/of_videomode.h>
+#include <video/videomode.h>
+
+/**
+ * of_get_videomode - get the videomode #<index> from devicetree
+ * @np - devicenode with the display_timings
+ * @vm - set to return value
+ * @index - index into list of display_timings
+ *	    (Set this to OF_USE_NATIVE_MODE to use whatever mode is
+ *	     specified as native mode in the DT.)
+ *
+ * DESCRIPTION:
+ * Get a list of all display timings and put the one
+ * specified by index into *vm. This function should only be used, if
+ * only one videomode is to be retrieved. A driver that needs to work
+ * with multiple/all videomodes should work with
+ * of_get_display_timings instead.
+ **/
+int of_get_videomode(struct device_node *np, struct videomode *vm,
+		     int index)
+{
+	struct display_timings *disp;
+	int ret;
+
+	disp = of_get_display_timings(np);
+	if (!disp) {
+		pr_err("%s: no timings specified\n", of_node_full_name(np));
+		return -EINVAL;
+	}
+
+	if (index == OF_USE_NATIVE_MODE)
+		index = disp->native_mode;
+
+	ret = videomode_from_timing(disp, vm, index);
+	if (ret)
+		return ret;
+
+	display_timings_release(disp);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(of_get_videomode);

include/video/of_display_timing.h

···
+/*
+ * Copyright 2012 Steffen Trumtrar <[e-mail]>
+ *
+ * display timings of helpers
+ *
+ * This file is released under the GPLv2
+ */
+
+#ifndef __LINUX_OF_DISPLAY_TIMING_H
+#define __LINUX_OF_DISPLAY_TIMING_H
+
+struct device_node;
+struct display_timings;
+
+#define OF_USE_NATIVE_MODE -1
+
+struct display_timings *of_get_display_timings(struct device_node *np);
+int of_display_timings_exist(struct device_node *np);
+
+#endif

include/video/of_videomode.h

···
+/*
+ * Copyright 2012 Steffen Trumtrar <[e-mail]>
+ *
+ * videomode of-helpers
+ *
+ * This file is released under the GPLv2
+ */
+
+#ifndef __LINUX_OF_VIDEOMODE_H
+#define __LINUX_OF_VIDEOMODE_H
+
+struct device_node;
+struct videomode;
+
+int of_get_videomode(struct device_node *np, struct videomode *vm,
+		     int index);
+
+#endif /* __LINUX_OF_VIDEOMODE_H */