Re: [PATCH] of: Overlay manager

From: Dmitry Shmidt
Date: Thu Sep 08 2016 - 17:15:11 EST

On Thu, Sep 8, 2016 at 2:08 PM, Frank Rowand <frowand.list@xxxxxxxxx> wrote:
> On 09/08/16 13:35, dimitrysh@xxxxxxxxxx wrote:
>> From e14eb45fa5a93c1bff8a6dfe7b6756e4ad72c579 Mon Sep 17 00:00:00 2001
>> From: Dmitry Shmidt <dimitrysh@xxxxxxxxxx>
>> Date: Wed, 24 Aug 2016 13:25:52 -0700
>> Subject: [PATCH] of: Overlay manager
>>
>> Overlay manager processes DT entries on demand.
>> It is chosen by CONFIG_OF_OVERLAY_MGR option.
>> These entries can be chosen from kernel command line:
>> overlay_mgr.overlay_dt_entry=hardware_cfg_0
>> DT contains main overlay_mng entry with all possible
>> HW config setups. And then kernel command line option
>> will allow to choose between them.
>>
>> Kernel DT entry:
>> overlay_mgr {
>> compatible = "linux,overlay_manager";
>> hardware_cfg_0 {
>> overlay@0 {
>> fragment@0 {
>> __overlay__ {
>> };
>> };
>> };
>> overlay@1 {
>> fragment@0 {
>> __overlay__ {
>> };
>> };
>> };
>> };
>> };
>
> What problem(s) are you trying to solve with this?

Currently the Linux kernel doesn't provide a way for boot time
selection of different possible board configurations, when the board
peripherals are specified via Device Tree.

Thus, this patch provides a driver which takes a boot option to
apply pre-defined device-tree overlay fragments on bootup. This
allows a single kernel/devicetree to be able to support a number of
different configurations by only changing a boot argument.

> What is the use case?

It is usually useful for development board when you can use
different peripherals. For example you want to use special
LCD panel. Using it will go on account of other stuff like GPIOs,
so you don't want it all the time. And it is not convenient to
apply new patches and to recompile the kernel. And this code
allows to choose LCD panel configuration from command line.

> -Frank
>
>>
>> Signed-off-by: Dmitry Shmidt <dimitrysh@xxxxxxxxxx>
>> Tested-by: John Stultz <john.stultz@xxxxxxxxxx>
>> Acked-by: John Stultz <john.stultz@xxxxxxxxxx>
>> ---
>> .../devicetree/bindings/of/overlay_mgr.txt | 32 ++++++++
>> drivers/of/Kconfig | 10 +++
>> drivers/of/Makefile | 1 +
>> drivers/of/overlay_mgr.c | 90 ++++++++++++++++++++++
>> 4 files changed, 133 insertions(+)
>> create mode 100644 Documentation/devicetree/bindings/of/overlay_mgr.txt
>> create mode 100644 drivers/of/overlay_mgr.c
>>
>> diff --git a/Documentation/devicetree/bindings/of/overlay_mgr.txt b/Documentation/devicetree/bindings/of/overlay_mgr.txt
>> new file mode 100644
>> index 0000000..5f3ce4c
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/of/overlay_mgr.txt
>> @@ -0,0 +1,32 @@
>> +overlay_mgr
>> +
>> +Required properties:
>> +- compatible: "linux,overlay_manager";
>> +
>> +Optional properties:
>> +- starts from the word "hardware": hardware_cfg_0
>> +
>> +These properties can be chosen from kernel command line:
>> +overlay_mgr.overlay_dt_entry=hardware_cfg_0
>> +DT contains main overlay_mng entry with all possible
>> +HW config setups. And then kernel command line option
>> +will allow to choose between them.
>> +
>> +Example:
>> + overlay_mgr {
>> + compatible = "linux,overlay_manager";
>> + hardware_cfg_0 {
>> + overlay@0 {
>> + fragment@0 {
>> + __overlay__ {
>> + };
>> + };
>> + };
>> + overlay@1 {
>> + fragment@0 {
>> + __overlay__ {
>> + };
>> + };
>> + };
>> + };
>> + };
>> diff --git a/drivers/of/Kconfig b/drivers/of/Kconfig
>> index e2a4841..e3eb06d 100644
>> --- a/drivers/of/Kconfig
>> +++ b/drivers/of/Kconfig
>> @@ -112,4 +112,14 @@ config OF_OVERLAY
>> While this option is selected automatically when needed, you can
>> enable it manually to improve device tree unit test coverage.
>>
>> +config OF_OVERLAY_MGR
>> + bool "Enable Overlay manager"
>> + default n
>> + depends on OF_OVERLAY
>> + help
>> + Enables Overlay manager - it accepts DT entry from command line
>> + overlay_mgr.overlay_dt_entry=<name> and applies all overlays in
>> + it to current DT. It is also possible to apply predefined DT
>> + entry on the fly by writing it to 'current_overlay' sysfs entry.
>> +
>> endif # OF
>> diff --git a/drivers/of/Makefile b/drivers/of/Makefile
>> index 156c072..3bddd19 100644
>> --- a/drivers/of/Makefile
>> +++ b/drivers/of/Makefile
>> @@ -14,5 +14,6 @@ obj-$(CONFIG_OF_MTD) += of_mtd.o
>> obj-$(CONFIG_OF_RESERVED_MEM) += of_reserved_mem.o
>> obj-$(CONFIG_OF_RESOLVE) += resolver.o
>> obj-$(CONFIG_OF_OVERLAY) += overlay.o
>> +obj-$(CONFIG_OF_OVERLAY_MGR) += overlay_mgr.o
>>
>> obj-$(CONFIG_OF_UNITTEST) += unittest-data/
>> diff --git a/drivers/of/overlay_mgr.c b/drivers/of/overlay_mgr.c
>> new file mode 100644
>> index 0000000..1fdeb0a
>> --- /dev/null
>> +++ b/drivers/of/overlay_mgr.c
>> @@ -0,0 +1,90 @@
>> +/*
>> + * Overlay manager that allows to apply list of overlays from DT entry
>> + *
>> + * Copyright (C) 2016 Google, Inc.
>> + *
>> + * This software is licensed under the terms of the GNU General Public
>> + * License version 2, as published by the Free Software Foundation, and
>> + * may be copied, distributed, and modified under those terms.
>> + *
>> + * This program is distributed in the hope that it will be useful,
>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
>> + * GNU General Public License for more details.
>> + */
>> +
>> +#include <linux/module.h>
>> +#include <linux/moduleparam.h>
>> +#include <linux/kernel.h>
>> +#include <linux/of.h>
>> +#include <linux/platform_device.h>
>> +
>> +static char *of_overlay_dt_entry;
>> +module_param_named(overlay_dt_entry, of_overlay_dt_entry, charp, 0644);
>> +
>> +static int of_overlay_mgr_apply_overlay(struct device_node *onp)
>> +{
>> + int ret;
>> +
>> + ret = of_overlay_create(onp);
>> + if (ret < 0) {
>> + pr_err("overlay_mgr: fail to create overlay: %d\n", ret);
>> + of_node_put(onp);
>> + return ret;
>> + }
>> + pr_info("overlay_mgr: %s overlay applied\n", onp->name);
>> + return 0;
>> +}
>> +
>> +static int of_overlay_mgr_apply_dt(struct device *dev, char *dt_entry)
>> +{
>> + struct device_node *enp = dev->of_node;
>> + struct device_node *next;
>> + struct device_node *prev = NULL;
>> +
>> + if (!enp) {
>> + pr_err("overlay_mgr: no dt entry\n");
>> + return -ENODEV;
>> + }
>> +
>> + enp = of_get_child_by_name(enp, dt_entry);
>> + if (!enp) {
>> + pr_err("overlay_mgr: dt entry %s not found\n", dt_entry);
>> + return -ENODEV;
>> + }
>> + pr_info("overlay_mgr: apply %s dt entry\n", enp->name);
>> + while ((next = of_get_next_available_child(enp, prev)) != NULL) {
>> + if (strncmp(next->name, "overlay", 7) == 0)
>> + of_overlay_mgr_apply_overlay(next);
>> + prev = next;
>> + }
>> + return 0;
>> +}
>> +
>> +static int of_overlay_mgr_probe(struct platform_device *pdev)
>> +{
>> + if (!of_overlay_dt_entry)
>> + return 0;
>> + of_overlay_mgr_apply_dt(&pdev->dev, of_overlay_dt_entry);
>> + return 0;
>> +}
>> +
>> +static const struct of_device_id of_overlay_mgr_match[] = {
>> + { .compatible = "linux,overlay_manager", },
>> + {}
>> +};
>> +
>> +static struct platform_driver of_overlay_mgr_driver = {
>> + .probe = of_overlay_mgr_probe,
>> + .driver = {
>> + .name = "overlay_manager",
>> + .of_match_table = of_match_ptr(of_overlay_mgr_match),
>> + },
>> +};
>> +
>> +static int __init of_overlay_mgr_init(void)
>> +{
>> + return platform_driver_register(&of_overlay_mgr_driver);
>> +}
>> +
>> +postcore_initcall(of_overlay_mgr_init);
>