Commit 8714c0ce authored by Steffen Trumtrar's avatar Steffen Trumtrar

video: add display_timing and videomode

Add display_timing structure and the according helper functions. This allows
the description of a display via its supported timing parameters.

Also, add helper functions to convert from display timings to a generic videomode

The struct display_timing specifies all needed parameters to describe the signal
properties of a display in one mode. This includes
    - ranges for signals that may have min-, max- and typical values
    - single integers for signals that can be on, off or are ignored
    - booleans for signals that are either on or off

As a display may support multiple modes like this, a struct display_timings is
added, that holds all given struct display_timing pointers and declares the
native mode of the display.

Although a display may state that a signal can be in a range, it is driven with
fixed values that indicate a videomode. Therefore graphic drivers don't need all
the information of struct display_timing, but would generate a videomode from
the given set of supported signal timings and work with that.

The video subsystems all define their own structs that describe a mode and work
with that (e.g. fb_videomode or drm_display_mode). To slowly replace all those
various structures and allow code reuse across those subsystems, add struct
videomode as a generic description.

This patch only includes the most basic fields in struct videomode. All missing
fields that are needed to have a really generic video mode description can be
added at a later stage.
Signed-off-by: default avatarSteffen Trumtrar <>
Reviewed-by: Thierry Reding's avatarThierry Reding <>
Acked-by: Thierry Reding's avatarThierry Reding <>
Tested-by: Thierry Reding's avatarThierry Reding <>
Tested-by: Philipp Zabel's avatarPhilipp Zabel <>
Reviewed-by: Laurent Pinchart's avatarLaurent Pinchart <>
Acked-by: Laurent Pinchart's avatarLaurent Pinchart <>
Tested-by: default avatarAfzal Mohammed <>
Tested-by: default avatarRob Clark <>
Tested-by: default avatarLeela Krishna Amudala <>
parent ea4f3111
......@@ -33,6 +33,12 @@ config VIDEO_OUTPUT_CONTROL
This framework adds support for low-level control of the video
output switch.
menuconfig FB
tristate "Support for frame buffer devices"
......@@ -168,3 +168,5 @@ obj-$(CONFIG_FB_VIRTUAL) += vfb.o
#video output switch sysfs driver
obj-$(CONFIG_DISPLAY_TIMING) += display_timing.o
obj-$(CONFIG_VIDEOMODE) += videomode.o
* generic display timing functions
* Copyright (c) 2012 Steffen Trumtrar <>, Pengutronix
* This file is released under the GPLv2
#include <linux/export.h>
#include <linux/slab.h>
#include <video/display_timing.h>
void display_timings_release(struct display_timings *disp)
if (disp->timings) {
unsigned int i;
for (i = 0; i < disp->num_timings; i++)
* generic display timing functions
* Copyright (c) 2012 Steffen Trumtrar <>, Pengutronix
* This file is released under the GPLv2
#include <linux/errno.h>
#include <linux/export.h>
#include <video/display_timing.h>
#include <video/videomode.h>
int videomode_from_timing(const struct display_timings *disp,
struct videomode *vm, unsigned int index)
struct display_timing *dt;
dt = display_timings_get(disp, index);
if (!dt)
return -EINVAL;
vm->pixelclock = display_timing_get_value(&dt->pixelclock, TE_TYP);
vm->hactive = display_timing_get_value(&dt->hactive, TE_TYP);
vm->hfront_porch = display_timing_get_value(&dt->hfront_porch, TE_TYP);
vm->hback_porch = display_timing_get_value(&dt->hback_porch, TE_TYP);
vm->hsync_len = display_timing_get_value(&dt->hsync_len, TE_TYP);
vm->vactive = display_timing_get_value(&dt->vactive, TE_TYP);
vm->vfront_porch = display_timing_get_value(&dt->vfront_porch, TE_TYP);
vm->vback_porch = display_timing_get_value(&dt->vback_porch, TE_TYP);
vm->vsync_len = display_timing_get_value(&dt->vsync_len, TE_TYP);
vm->dmt_flags = dt->dmt_flags;
vm->data_flags = dt->data_flags;
return 0;
* Copyright 2012 Steffen Trumtrar <>
* description of display timings
* This file is released under the GPLv2
#include <linux/bitops.h>
#include <linux/types.h>
/* VESA display monitor timing parameters */
/* display specific flags */
#define DISPLAY_FLAGS_DE_LOW BIT(0) /* data enable flag */
#define DISPLAY_FLAGS_PIXDATA_POSEDGE BIT(2) /* drive data on pos. edge */
#define DISPLAY_FLAGS_PIXDATA_NEGEDGE BIT(3) /* drive data on neg. edge */
* A single signal can be specified via a range of minimal and maximal values
* with a typical value, that lies somewhere inbetween.
struct timing_entry {
u32 min;
u32 typ;
u32 max;
enum timing_entry_index {
TE_MIN = 0,
TE_TYP = 1,
TE_MAX = 2,
* Single "mode" entry. This describes one set of signal timings a display can
* have in one setting. This struct can later be converted to struct videomode
* (see include/video/videomode.h). As each timing_entry can be defined as a
* range, one struct display_timing may become multiple struct videomodes.
* Example: hsync active high, vsync active low
* Active Video
* Video ______________________XXXXXXXXXXXXXXXXXXXXXX_____________________
* |<- sync ->|<- back ->|<----- active ----->|<- front ->|<- sync..
* | | porch | | porch |
* HSync _|¯¯¯¯¯¯¯¯¯¯|___________________________________________|¯¯¯¯¯¯¯¯¯
* VSync ¯|__________|¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯|_________
struct display_timing {
struct timing_entry pixelclock;
struct timing_entry hactive; /* hor. active video */
struct timing_entry hfront_porch; /* hor. front porch */
struct timing_entry hback_porch; /* hor. back porch */
struct timing_entry hsync_len; /* hor. sync len */
struct timing_entry vactive; /* ver. active video */
struct timing_entry vfront_porch; /* ver. front porch */
struct timing_entry vback_porch; /* ver. back porch */
struct timing_entry vsync_len; /* ver. sync len */
unsigned int dmt_flags; /* VESA DMT flags */
unsigned int data_flags; /* video data flags */
* This describes all timing settings a display provides.
* The native_mode is the default setting for this display.
* Drivers that can handle multiple videomodes should work with this struct and
* convert each entry to the desired end result.
struct display_timings {
unsigned int num_timings;
unsigned int native_mode;
struct display_timing **timings;
/* get value specified by index from struct timing_entry */
static inline u32 display_timing_get_value(const struct timing_entry *te,
enum timing_entry_index index)
switch (index) {
case TE_MIN:
return te->min;
case TE_TYP:
return te->typ;
case TE_MAX:
return te->max;
return te->typ;
/* get one entry from struct display_timings */
static inline struct display_timing *display_timings_get(const struct
display_timings *disp,
unsigned int index)
if (disp->num_timings > index)
return disp->timings[index];
return NULL;
void display_timings_release(struct display_timings *disp);
* Copyright 2012 Steffen Trumtrar <>
* generic videomode description
* This file is released under the GPLv2
#include <linux/types.h>
#include <video/display_timing.h>
* Subsystem independent description of a videomode.
* Can be generated from struct display_timing.
struct videomode {
unsigned long pixelclock; /* pixelclock in Hz */
u32 hactive;
u32 hfront_porch;
u32 hback_porch;
u32 hsync_len;
u32 vactive;
u32 vfront_porch;
u32 vback_porch;
u32 vsync_len;
unsigned int dmt_flags; /* VESA DMT flags */
unsigned int data_flags; /* video data flags */
* videomode_from_timing - convert display timing to videomode
* @disp: structure with all possible timing entries
* @vm: return value
* @index: index into the list of display timings in devicetree
* This function converts a struct display_timing to a struct videomode.
int videomode_from_timing(const struct display_timings *disp,
struct videomode *vm, unsigned int index);
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