Re: [PATCH v8 2/6] video: add of helper for videomode

This adds support for reading display timings from DT or/and convert one of those
timings to a videomode.
The of_display_timing implementation supports multiple children where each
property can have up to 3 values. All children are read into an array, that
can be queried.
of_get_videomode converts exactly one of that timings to a struct videomode.

Signed-off-by: Steffen Trumtrar <redacted>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
---
 .../devicetree/bindings/video/display-timings.txt  |  107 +++++++++++
 drivers/video/Kconfig                              |   13 ++
 drivers/video/Makefile                             |    2 +
 drivers/video/of_display_timing.c                  |  186 ++++++++++++++++++++
 drivers/video/of_videomode.c                       |   47 +++++
 include/linux/of_display_timings.h                 |   19 ++
 include/linux/of_videomode.h                       |   15 ++
 7 files changed, 389 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/video/display-timings.txt
 create mode 100644 drivers/video/of_display_timing.c
 create mode 100644 drivers/video/of_videomode.c
 create mode 100644 include/linux/of_display_timings.h
 create mode 100644 include/linux/of_videomode.h

diff --git a/Documentation/devicetree/bindings/video/display-timings.txt b/Documentation/devicetree/bindings/video/display-timings.txt
new file mode 100644
index 0000000..e22e2fd
--- /dev/null
+++ b/Documentation/devicetree/bindings/video/display-timings.txt

@@ -0,0 +1,107 @@
+display-timings 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.
+
+timings-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: displayclock 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-inverted : pixelclock is inverted/non-inverted/ignored
+ - interlaced (bool)
+ - doublescan (bool)
+
+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
+
+struct display_timing
+==========> +
+  +----------+---------------------------------------------+----------+-------+
+  |          |                ↑                            |          |       |
+  |          |                |vback_porch                 |          |       |
+  |          |                ↓                            |          |       |
+  +----------###############################################----------+-------+
+  |          #                ↑                            #          |       |
+  |          #                |                            #          |       |
+  |  hback   #                |                            #  hfront  | hsync |
+  |   porch  #                |       hactive              #  porch   |  len  |
+  |<-------->#<---------------+--------------------------->#<-------->|<----->|
+  |          #                |                            #          |       |
+  |          #                |vactive                     #          |       |
+  |          #                |                            #          |       |
+  |          #                ↓                            #          |       |
+  +----------###############################################----------+-------+
+  |          |                ↑                            |          |       |
+  |          |                |vfront_porch                |          |       |
+  |          |                ↓                            |          |       |
+  +----------+---------------------------------------------+----------+-------+
+  |          |                ↑                            |          |       |
+  |          |                |vsync_len                   |          |       |
+  |          |                ↓                            |          |       |
+  +----------+---------------------------------------------+----------+-------+
+
+
+Example:
+
+       display-timings {
+               native-mode = <&timing0>;
+               timing0: 1920p24 {
+                       /* 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 <min typ max>-tuples 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>;
+       };

diff --git a/drivers/video/Kconfig b/drivers/video/Kconfig
index 2a23b18..a324457 100644
--- a/drivers/video/Kconfig
+++ b/drivers/video/Kconfig

@@ -39,6 +39,19 @@ config DISPLAY_TIMING
 config VIDEOMODE
        bool

+config OF_DISPLAY_TIMING
+       def_bool y
+       select DISPLAY_TIMING
+       help
+         helper to parse display timings from the devicetree
+
+config OF_VIDEOMODE
+       def_bool y
+       select VIDEOMODE
+       select OF_DISPLAY_TIMING
+       help
+         helper to get videomodes from the devicetree
+
 menuconfig FB
        tristate "Support for frame buffer devices"
        ---help---

diff --git a/drivers/video/Makefile b/drivers/video/Makefile
index fc30439..b936b00 100644
--- a/drivers/video/Makefile
+++ b/drivers/video/Makefile

@@ -168,4 +168,6 @@ obj-$(CONFIG_FB_VIRTUAL)          += vfb.o
 #video output switch sysfs driver
 obj-$(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

diff --git a/drivers/video/of_display_timing.c b/drivers/video/of_display_timing.c
new file mode 100644
index 0000000..0bd30cc
--- /dev/null
+++ b/drivers/video/of_display_timing.c

@@ -0,0 +1,186 @@
+/*
+ * OF helpers for parsing display timings
+ *
+ * Copyright (c) 2012 Steffen Trumtrar <s.trumtrar@pengutronix.de>, Pengutronix
+ *
+ * based on of_videomode.c by Sascha Hauer <s.hauer@pengutronix.de>
+ *
+ * This file is released under the GPLv2
+ */
+#include <linux/of.h>
+#include <linux/slab.h>
+#include <linux/export.h>
+#include <linux/of_display_timings.h>
+
+/**
+ * parse_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_property(struct device_node *np, 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", __func__, 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", __func__, 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;
+       int ret = 0;
+
+       dt = kzalloc(sizeof(*dt), GFP_KERNEL);
+       if (!dt) {
+               pr_err("%s: could not allocate display_timing struct\n", __func__);
+               return NULL;
+       }
+
+       ret |= parse_property(np, "hback-porch", &dt->hback_porch);
+       ret |= parse_property(np, "hfront-porch", &dt->hfront_porch);
+       ret |= parse_property(np, "hactive", &dt->hactive);
+       ret |= parse_property(np, "hsync-len", &dt->hsync_len);
+       ret |= parse_property(np, "vback-porch", &dt->vback_porch);
+       ret |= parse_property(np, "vfront-porch", &dt->vfront_porch);
+       ret |= parse_property(np, "vactive", &dt->vactive);
+       ret |= parse_property(np, "vsync-len", &dt->vsync_len);
+       ret |= parse_property(np, "clock-frequency", &dt->pixelclock);
+
+       of_property_read_u32(np, "vsync-active", &dt->vsync_pol_active);
+       of_property_read_u32(np, "hsync-active", &dt->hsync_pol_active);
+       of_property_read_u32(np, "de-active", &dt->de_pol_active);
+       of_property_read_u32(np, "pixelclk-inverted", &dt->pixelclk_pol);
+       dt->interlaced = of_property_read_bool(np, "interlaced");
+       dt->doublescan = of_property_read_bool(np, "doublescan");
+
+       if (ret) {
+               pr_err("%s: error reading timing properties\n", __func__);
+               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", __func__);
+               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", __func__);
+               return NULL;
+       }
+
+       disp = kzalloc(sizeof(*disp), GFP_KERNEL);
+       if (!disp)
+               return -ENOMEM;
+
+       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 (!entry) {
+               pr_err("%s: no timing specifications given\n", __func__);
+               return NULL;
+       }
+
+       pr_info("%s: using %s as default timing\n", __func__, entry->name);
+
+       native_mode = entry;
+
+       disp->num_timings = of_get_child_count(timings_np);
+       disp->timings = kzalloc(sizeof(struct display_timing *)*disp->num_timings,
+                               GFP_KERNEL);
+       if (!disp->timings)
+               return -ENOMEM;