linux-kernel - Re: [PATCH v2 1/3] power: reset: read priority from device tree

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Date:	Mon, 1 Dec 2014 09:42:15 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	Feng Kan <fkan@....com>
Cc:	Stefan Agner <stefan@...er.ch>, shawn.guo@...aro.org,
	kernel@...gutronix.de, Arnd Bergmann <arnd@...db.de>,
	sre@...nel.org, grant.likely@...aro.org, robh+dt@...nel.org,
	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	David Woodhouse <dwmw2@...radead.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] power: reset: read priority from device tree

On Mon, Dec 01, 2014 at 09:38:09AM -0800, Feng Kan wrote:
> On Mon, Dec 1, 2014 at 9:29 AM, Stefan Agner <stefan@...er.ch> wrote:
> > On 2014-12-01 18:15, Feng Kan wrote:
> >> On Mon, Dec 1, 2014 at 9:03 AM, Stefan Agner <stefan@...er.ch> wrote:
> >>> This patch adds an optional property which allows to specify the
> >>> reset source priority. This priority is used by the kernel restart
> >>> handler call chain to sort out the proper reset/restart method.
> >>> Depending on the power design of a board or other machine/board
> >>> specific peculiarity, it is not possible to pick a generic priority.
> >>>
> >>> Signed-off-by: Stefan Agner <stefan@...er.ch>
> >>> ---
> >>>  Documentation/devicetree/bindings/power/reset/syscon-reboot.txt | 3 +++
> >>>  drivers/power/reset/syscon-reboot.c                             | 5 ++++-
> >>>  2 files changed, 7 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/Documentation/devicetree/bindings/power/reset/syscon-reboot.txt b/Documentation/devicetree/bindings/power/reset/syscon-reboot.txt
> >>> index 1190631..ee41d9c 100644
> >>> --- a/Documentation/devicetree/bindings/power/reset/syscon-reboot.txt
> >>> +++ b/Documentation/devicetree/bindings/power/reset/syscon-reboot.txt
> >>> @@ -11,6 +11,9 @@ Required properties:
> >>>  - offset: offset in the register map for the reboot register (in bytes)
> >>>  - mask: the reset value written to the reboot register (32 bit access)
> >>>
> >>> +Optional properties:
> >>> +- priority: define the priority of the reset (0-255, defaults to 128)
> >>> +
> >>>  Default will be little endian mode, 32 bit access only.
> >>>
> >>>  Examples:
> >>> diff --git a/drivers/power/reset/syscon-reboot.c b/drivers/power/reset/syscon-reboot.c
> >>> index 815b901..3060d6b 100644
> >>> --- a/drivers/power/reset/syscon-reboot.c
> >>> +++ b/drivers/power/reset/syscon-reboot.c
> >>> @@ -67,8 +67,11 @@ static int syscon_reboot_probe(struct platform_device *pdev)
> >>>         if (of_property_read_u32(pdev->dev.of_node, "mask", &ctx->mask))
> >>>                 return -EINVAL;
> >>>
> >>> -       ctx->restart_handler.notifier_call = syscon_restart_handle;
> >>>         ctx->restart_handler.priority = 128;
> >>> +       of_property_read_u32(pdev->dev.of_node, "priority",
> >>> +                            &ctx->restart_handler.priority);
> >>
> >> What is this for?
> >
> > What do you mean? The moved line "ctx->restart_handler.notifier_call =
> > syscon_restart_handle;"? When one reads the diff, it looks like that
> > line was moved, in fact I tried to keep the of_property_read function
> > calls together. But I had to move the assignation of the default
> > priority in front of restart_handler.priority. That's what is the
> > outcome...
> 
> I believe Guenter explained above already. Actually this help to solve one of
> my problem. Thanks.

Since Mark doesn't seem to be happy with the idea of making the priority
dt-configurable, the alternative might be to just set a higher priority for
syscon triggered resets, as suggested by Stefan. Not as flexible, but it
should be ok for most use cases.

Guenter
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