Re: [PATCH 1/2 v6] of: add helper to parse display timings

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Hi,

On Thu, 2012-10-04 at 19:59 +0200, Steffen Trumtrar wrote:
> Signed-off-by: Steffen Trumtrar <s.trumtrar@xxxxxxxxxxxxxx>
> ---
>  .../devicetree/bindings/video/display-timings.txt  |  222 ++++++++++++++++++++
>  drivers/of/Kconfig                                 |    5 +
>  drivers/of/Makefile                                |    1 +
>  drivers/of/of_display_timings.c                    |  183 ++++++++++++++++
>  include/linux/of_display_timings.h                 |   85 ++++++++
>  5 files changed, 496 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/video/display-timings.txt
>  create mode 100644 drivers/of/of_display_timings.c
>  create mode 100644 include/linux/of_display_timings.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..45e39bd
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/video/display-timings.txt
> @@ -0,0 +1,222 @@
> +display-timings bindings
> +==================
> +
> +display-timings-node
> +------------
> +
> +required properties:
> + - none
> +
> +optional properties:
> + - default-timing: the default timing value
> +
> +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: displayclock in Hz
> +
> +optional properties:
> + - hsync-active-high (bool): Hsync pulse is active high
> + - vsync-active-high (bool): Vsync pulse is active high
> + - de-active-high (bool): Data-Enable pulse is active high
> + - pixelclk-inverted (bool): pixelclock is inverted
> + - interlaced (bool)
> + - doublescan (bool)

I think bool should be generally used for things that are on/off, like
interlace. For hsync-active-high & others I'd rather have 0/1 values as
others already suggested.

> +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 default-timing can be specified.
> +
> +The parameters are defined as
> +
> +struct signal_timing
> +===================
> +
> +  +----------+---------------------------------------------+----------+-------+
> +  |          |                ↑                            |          |       |
> +  |          |                |vback_porch                 |          |       |
> +  |          |                ↓                            |          |       |
> +  +----------###############################################----------+-------+
> +  |          #                ↑                            #          |       |
> +  |          #                |                            #          |       |
> +  |  hback   #                |                            #  hfront  | hsync |
> +  |   porch  #                |       hactive              #  porch   |  len  |
> +  |<-------->#<---------------+--------------------------->#<-------->|<----->|
> +  |          #                |                            #          |       |
> +  |          #                |vactive                     #          |       |
> +  |          #                |                            #          |       |
> +  |          #                ↓                            #          |       |
> +  +----------###############################################----------+-------+
> +  |          |                ↑                            |          |       |
> +  |          |                |vfront_porch                |          |       |
> +  |          |                ↓                            |          |       |
> +  +----------+---------------------------------------------+----------+-------+
> +  |          |                ↑                            |          |       |
> +  |          |                |vsync_len                   |          |       |
> +  |          |                ↓                            |          |       |
> +  +----------+---------------------------------------------+----------+-------+
> +
> +
> +Example:
> +
> +	display-timings {
> +		default-timing = <&timing0>;
> +		timing0: 1920p24 {
> +			/* 1920x1080p24 */

I think this is commonly called 1080p24.

> +			clock = <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-high;
> +		};
> +	};
> +
> +Every 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 = <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>;
> +	};
> +
> +Usage in backend
> +================
> +
> +A backend driver may choose to use the display-timings directly and convert the timing
> +ranges to a suitable mode. Or it may just use the conversion of the display timings
> +to the required mode via the generic videomode struct.
> +
> +					dtb
> +					 |
> +					 |  of_get_display_timing_list
> +					 ↓
> +			      struct display_timings
> +					 |
> +					 |  videomode_from_timing
> +					 ↓
> +			    ---  struct videomode ---
> +			    |			    |
> + videomode_to_displaymode   |			    |   videomode_to_fb_videomode
> +		            ↓			    ↓
> +		     drm_display_mode         fb_videomode
> +
> +The functions of_get_fb_videomode and of_get_display_mode are provided
> +to conveniently get the respective mode representation from the devicetree.
> +
> +Conversion to videomode
> +=======================
> +
> +As device drivers normally work with some kind of video mode, the timings can be
> +converted (may be just a simple copying of the typical value) to a generic videomode
> +structure which then can be converted to the according mode used by the backend.
> +
> +Supported modes
> +===============
> +
> +The generic videomode read in by the driver can be converted to the following
> +modes with the following parameters
> +
> +struct fb_videomode
> +===================
> +
> +  +----------+---------------------------------------------+----------+-------+
> +  |          |                ↑                            |          |       |
> +  |          |                |upper_margin                |          |       |
> +  |          |                ↓                            |          |       |
> +  +----------###############################################----------+-------+
> +  |          #                ↑                            #          |       |
> +  |          #                |                            #          |       |
> +  |          #                |                            #          |       |
> +  |          #                |                            #          |       |
> +  |   left   #                |                            #  right   | hsync |
> +  |  margin  #                |       xres                 #  margin  |  len  |
> +  |<-------->#<---------------+--------------------------->#<-------->|<----->|
> +  |          #                |                            #          |       |
> +  |          #                |                            #          |       |
> +  |          #                |                            #          |       |
> +  |          #                |yres                        #          |       |
> +  |          #                |                            #          |       |
> +  |          #                |                            #          |       |
> +  |          #                |                            #          |       |
> +  |          #                |                            #          |       |
> +  |          #                |                            #          |       |
> +  |          #                |                            #          |       |
> +  |          #                |                            #          |       |
> +  |          #                |                            #          |       |
> +  |          #                ↓                            #          |       |
> +  +----------###############################################----------+-------+
> +  |          |                ↑                            |          |       |
> +  |          |                |lower_margin                |          |       |
> +  |          |                ↓                            |          |       |
> +  +----------+---------------------------------------------+----------+-------+
> +  |          |                ↑                            |          |       |
> +  |          |                |vsync_len                   |          |       |
> +  |          |                ↓                            |          |       |
> +  +----------+---------------------------------------------+----------+-------+
> +
> +clock in nanoseconds
> +
> +struct drm_display_mode
> +=======================
> +
> +  +----------+---------------------------------------------+----------+-------+
> +  |          |                                             |          |       |  ↑
> +  |          |                                             |          |       |  |
> +  |          |                                             |          |       |  |
> +  +----------###############################################----------+-------+  |
> +  |          #   ↑         ↑          ↑                    #          |       |  |
> +  |          #   |         |          |                    #          |       |  |
> +  |          #   |         |          |                    #          |       |  |
> +  |          #   |         |          |                    #          |       |  |
> +  |          #   |         |          |                    #          |       |  |
> +  |          #   |         |          |       hdisplay     #          |       |  |
> +  |          #<--+--------------------+------------------->#          |       |  |
> +  |          #   |         |          |                    #          |       |  |
> +  |          #   |vsync_start         |                    #          |       |  |
> +  |          #   |         |          |                    #          |       |  |
> +  |          #   |         |vsync_end |                    #          |       |  |
> +  |          #   |         |          |vdisplay            #          |       |  |
> +  |          #   |         |          |                    #          |       |  |
> +  |          #   |         |          |                    #          |       |  |
> +  |          #   |         |          |                    #          |       |  | vtotal
> +  |          #   |         |          |                    #          |       |  |
> +  |          #   |         |          |     hsync_start    #          |       |  |
> +  |          #<--+---------+----------+------------------------------>|       |  |
> +  |          #   |         |          |                    #          |       |  |
> +  |          #   |         |          |     hsync_end      #          |       |  |
> +  |          #<--+---------+----------+-------------------------------------->|  |
> +  |          #   |         |          ↓                    #          |       |  |
> +  +----------####|#########|################################----------+-------+  |
> +  |          |   |         |                               |          |       |  |
> +  |          |   |         |                               |          |       |  |
> +  |          |   ↓         |                               |          |       |  |
> +  +----------+-------------+-------------------------------+----------+-------+  |
> +  |          |             |                               |          |       |  |
> +  |          |             |                               |          |       |  |
> +  |          |             ↓                               |          |       |  ↓
> +  +----------+---------------------------------------------+----------+-------+
> +                                   htotal
> +   <------------------------------------------------------------------------->
> +
> +clock in kilohertz
> diff --git a/drivers/of/Kconfig b/drivers/of/Kconfig
> index dfba3e6..646deb0 100644
> --- a/drivers/of/Kconfig
> +++ b/drivers/of/Kconfig
> @@ -83,4 +83,9 @@ config OF_MTD
>  	depends on MTD
>  	def_bool y
>  
> +config OF_DISPLAY_TIMINGS
> +	def_bool y
> +	help
> +	  helper to parse display timings from the devicetree
> +
>  endmenu # OF
> diff --git a/drivers/of/Makefile b/drivers/of/Makefile
> index e027f44..c8e9603 100644
> --- a/drivers/of/Makefile
> +++ b/drivers/of/Makefile
> @@ -11,3 +11,4 @@ obj-$(CONFIG_OF_MDIO)	+= of_mdio.o
>  obj-$(CONFIG_OF_PCI)	+= of_pci.o
>  obj-$(CONFIG_OF_PCI_IRQ)  += of_pci_irq.o
>  obj-$(CONFIG_OF_MTD)	+= of_mtd.o
> +obj-$(CONFIG_OF_DISPLAY_TIMINGS) += of_display_timings.o
> diff --git a/drivers/of/of_display_timings.c b/drivers/of/of_display_timings.c
> new file mode 100644
> index 0000000..e47bc63
> --- /dev/null
> +++ b/drivers/of/of_display_timings.c
> @@ -0,0 +1,183 @@
> +/*
> + * OF helpers for parsing display timings
> + * 
> + * Copyright (c) 2012 Steffen Trumtrar <s.trumtrar@xxxxxxxxxxxxxx>, Pengutronix
> + * 
> + * based on of_videomode.c by Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>
> + *
> + * 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>
> +
> +/* every signal_timing can be specified with either
> + * just the typical value or a range consisting of
> + * min/typ/max.
> + * This function helps handling this
> + */

The comment is not according to kernel coding style. And I'd start the
sentence with a capital letter =).

> +static int parse_property(struct device_node *np, char *name,
> +				struct timing_entry *result)
> +{
> +	struct property *prop;
> +	int length;
> +	int cells;
> +	int 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_array(np, name, &result->typ, cells);
> +	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;
> +}
> +
> +struct signal_timing *of_get_display_timing(struct device_node *np)
> +{
> +	struct signal_timing *st;
> +	int ret = 0;
> +
> +	st = kzalloc(sizeof(*st), GFP_KERNEL);
> +
> +	if (!st) {
> +		pr_err("%s: could not allocate signal_timing struct\n", __func__);
> +		return NULL;
> +	}
> +
> +	ret |= parse_property(np, "hback-porch", &st->hback_porch);
> +	ret |= parse_property(np, "hfront-porch", &st->hfront_porch);
> +	ret |= parse_property(np, "hactive", &st->hactive);
> +	ret |= parse_property(np, "hsync-len", &st->hsync_len);
> +	ret |= parse_property(np, "vback-porch", &st->vback_porch);
> +	ret |= parse_property(np, "vfront-porch", &st->vfront_porch);
> +	ret |= parse_property(np, "vactive", &st->vactive);
> +	ret |= parse_property(np, "vsync-len", &st->vsync_len);
> +	ret |= parse_property(np, "clock", &st->pixelclock);
> +
> +	st->vsync_pol_active_high = of_property_read_bool(np, "vsync-active-high");
> +	st->hsync_pol_active_high = of_property_read_bool(np, "hsync-active-high");
> +	st->de_pol_active_high = of_property_read_bool(np, "de-active-high");
> +	st->pixelclk_pol_inverted = of_property_read_bool(np, "pixelclk-inverted");
> +	st->interlaced = of_property_read_bool(np, "interlaced");
> +	st->doublescan = of_property_read_bool(np, "doublescan");
> +
> +	if (ret) {
> +		pr_err("%s: error reading timing properties\n", __func__);
> +		return NULL;
> +	}
> +
> +	return st;
> +}
> +EXPORT_SYMBOL_GPL(of_get_display_timing);
> +
> +struct display_timings *of_get_display_timing_list(struct device_node *np)
> +{
> +	struct device_node *timings_np;
> +	struct device_node *entry;
> +	struct display_timings *disp;
> +	char *default_timing;
> +
> +	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);
> +
> +	entry = of_parse_phandle(timings_np, "default-timing", 0);
> +
> +	if (!entry) {
> +		pr_info("%s: no default-timing specified\n", __func__);
> +		entry = of_find_node_by_name(np, "timing");
> +	}

If "default-timing" property is optional, I don't see any need for the
pr_info above, as it should be business as usual if the property doesn't
exist.

If the default-timing property doesn't exist, wouldn't it be simpler to
get the first subnode, instead of looking one with "timing" name?

> +
> +	if (!entry) {
> +		pr_info("%s: no timing specifications given\n", __func__);
> +		return disp;
> +	}

Again, I don't think the pr_info is needed if this is a normal case.
Then again, perhaps this could be an error? Why would there be a display
node without any timings?

> +
> +	pr_info("%s: using %s as default timing\n", __func__, entry->name);
> +
> +	default_timing = (char *)entry->full_name;

const char *?

> +
> +	disp->num_timings = 0;
> +
> +	for_each_child_of_node(timings_np, entry) {
> +		disp->num_timings++;
> +	}

No need for { }

> +	disp->timings = kzalloc(sizeof(struct signal_timing *)*disp->num_timings,
> +				GFP_KERNEL);
> +
> +	disp->num_timings = 0;
> +
> +	for_each_child_of_node(timings_np, entry) {
> +		struct signal_timing *st;
> +
> +		st = of_get_display_timing(entry);
> +
> +		if (!st)
> +			continue;
> +
> +		if (strcmp(default_timing, entry->full_name) == 0)
> +			disp->default_timing = disp->num_timings;

I don't see you setting disp->default_timing to OF_DEFAULT_TIMING in
case there's no default_timing found.

Or, at least I presume OF_DEFAULT_TIMING is meant to mark non-existing
default timing. The name OF_DEFAULT_TIMING is not very descriptive to
me.

Would it make more sense to have the disp->default_timing as a pointer
to the timing, instead of index? Then a NULL value would mark a
non-existing default timing.

> +		disp->timings[disp->num_timings] = st;
> +		disp->num_timings++;
> +	}
> +
> +
> +	of_node_put(timings_np);
> +
> +	if (disp->num_timings >= 0)
> +		pr_info("%s: got %d timings. Using timing #%d as default\n", __func__,
> +			disp->num_timings , disp->default_timing + 1);
> +	else
> +		pr_info("%s: no timings specified\n", __func__);
> +
> +	return disp;
> +}
> +EXPORT_SYMBOL_GPL(of_get_display_timing_list);
> +
> +int of_display_timings_exists(struct device_node *np)
> +{
> +	struct device_node *timings_np;
> +	struct device_node *default_np;
> +
> +	if (!np)
> +		return -EINVAL;
> +
> +	timings_np = of_parse_phandle(np, "display-timings", 0);
> +
> +	if (!timings_np)
> +		return -EINVAL;
> +
> +	default_np = of_parse_phandle(np, "default-timing", 0);
> +
> +	if (default_np)
> +		return 0;
> +
> +	return -EINVAL;
> +}
> +EXPORT_SYMBOL_GPL(of_display_timings_exists);
> diff --git a/include/linux/of_display_timings.h b/include/linux/of_display_timings.h
> new file mode 100644
> index 0000000..1ad719e
> --- /dev/null
> +++ b/include/linux/of_display_timings.h
> @@ -0,0 +1,85 @@
> +/*
> + * Copyright 2012 Steffen Trumtrar <s.trumtrar@xxxxxxxxxxxxxx>
> + *
> + * description of display timings
> + *
> + * This file is released under the GPLv2
> + */
> +
> +#ifndef __LINUX_OF_DISPLAY_TIMINGS_H
> +#define __LINUX_OF_DISPLAY_TIMINGS_H
> +
> +#define OF_DEFAULT_TIMING -1
> +
> +struct display_timings {
> +	unsigned int num_timings;
> +	unsigned int default_timing;
> +
> +	struct signal_timing **timings;

Should this be a pointer to a const array of const data? Is there ever
need to change them after they've been read from DT?

> +};
> +
> +struct timing_entry {
> +	u32 min;
> +	u32 typ;
> +	u32 max;
> +};
> +
> +struct signal_timing {
> +	struct timing_entry pixelclock;
> +
> +	struct timing_entry hactive;
> +	struct timing_entry hfront_porch;
> +	struct timing_entry hback_porch;
> +	struct timing_entry hsync_len;
> +
> +	struct timing_entry vactive;
> +	struct timing_entry vfront_porch;
> +	struct timing_entry vback_porch;
> +	struct timing_entry vsync_len;
> +
> +	bool vsync_pol_active_high;
> +	bool hsync_pol_active_high;
> +	bool de_pol_active_high;
> +	bool pixelclk_pol_inverted;
> +	bool interlaced;
> +	bool doublescan;
> +};
> +
> +struct display_timings *of_get_display_timing_list(struct device_node *np);
> +struct signal_timing *of_get_display_timing(struct device_node *np);
> +int of_display_timings_exists(struct device_node *np);
> +
> +/* placeholder function until ranges are really needed */
> +static inline u32 signal_timing_get_value(struct timing_entry *te, int index)
> +{
> +	return te->typ;
> +}
> +
> +static inline void timings_release(struct display_timings *disp)
> +{
> +	int i;
> +
> +	for (i = 0; i < disp->num_timings; i++)
> +		kfree(disp->timings[i]);
> +}
> +
> +static inline void display_timings_release(struct display_timings *disp)
> +{
> +	timings_release(disp);
> +	kfree(disp->timings);
> +}
> +
> +static inline struct signal_timing *display_timings_get(struct display_timings *disp,
> +							 int index)
> +{
> +	struct signal_timing *st;
> +
> +	if (disp->num_timings > index) {
> +		st = disp->timings[index];
> +		return st;
> +	}
> +	else
> +		return NULL;
> +}

Why do you have these functions in the header file?

 Tomi

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