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Message-ID: <20141201181811.GB22023@leverpostej> Date: Mon, 1 Dec 2014 18:18:11 +0000 From: Mark Rutland <mark.rutland@....com> To: Guenter Roeck <linux@...ck-us.net> Cc: Stefan Agner <stefan@...er.ch>, "shawn.guo@...aro.org" <shawn.guo@...aro.org>, "kernel@...gutronix.de" <kernel@...gutronix.de>, "arnd@...db.de" <arnd@...db.de>, "sre@...nel.org" <sre@...nel.org>, "fkan@....com" <fkan@....com>, "grant.likely@...aro.org" <grant.likely@...aro.org>, "robh+dt@...nel.org" <robh+dt@...nel.org>, "dbaryshkov@...il.com" <dbaryshkov@...il.com>, "dwmw2@...radead.org" <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 06:12:55PM +0000, Guenter Roeck wrote: > On Mon, Dec 01, 2014 at 05:59:08PM +0000, Mark Rutland wrote: > > On Mon, Dec 01, 2014 at 05:51:34PM +0000, Guenter Roeck wrote: > > > On Mon, Dec 01, 2014 at 05:41:00PM +0000, Mark Rutland wrote: > > > > On Mon, Dec 01, 2014 at 05:24:37PM +0000, Stefan Agner wrote: > > > > > On 2014-12-01 18:11, Mark Rutland wrote: > > > > > > On Mon, Dec 01, 2014 at 05:03:07PM +0000, Stefan Agner 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) > > > > > >> + > > > > > > > > > > > > NAK. This is a leak of Linux-internal details. > > > > > > > > > > > > What is this necessary for? > > > > > > > > > > > > Mark. > > > > > > > > > > Hi Mark, > > > > > > > > > > In my case, it is necessary to be called ahead of the watchdog, which > > > > > has a priority of 128. This syscon-reboot driver currently has a default > > > > > priority of 128 too. I could live with a higher default priority for the > > > > > syscon-reboot driver, in fact I proposed that in the discussion of v1 of > > > > > that patch: > > > > > https://lkml.org/lkml/2014/11/28/484 > > > > > > > > Thanks for the link. > > > > > > > > > IMHO, this priority might make sense for most cases, I guess that > > > > > dedicated "syscon" capabilities are usually better suited as a reboot > > > > > source than watchdog. > > > > > > > > I would think likewise. > > > > > > > > > If dt, then the question which arises: If there are different > > > > > capabilities to reset/reboot a whole system, how do we reflect which is > > > > > the best suited one in dt? > > > > > > > > I'm not sure, but I don't think that exposing a priority variable in > > > > this way is the best, because it implicitly relies on what the kernel > > > > may have selected for other devices and/or FW interfaces, which may not > > > > have been described in DT. > > > > > > > > So if we can get away with a fixed priority for now, then I would prefer > > > > that. > > > > > > > > Otherwise, I would imagine that most systems have a single preferred > > > > mechanism with some possible fallback(s), for which a single > > > > preferred-poweroff property might suffice, and has better interaction > > > > w.r.t. priority (in that it should _always_ be tried first). Even that's > > > > difficult to reconcile with FW bindings though, especially EFI (which we > > > > sometimes must use in preference for variable storage and capsule > > > > updates). > > > > > > > Hi mark, > > > > > > reboot, not poweroff, but I like that idea; it is system independent, > > > and I agree that there should be only one "preferred-reboot" mechanism. > > > If we need more we can always add something like "fallback-reboot". > > > > Ah, sorry, I got myself confused regarding reboot/poweroff. Goot to hear > > we agree on the preferred-$X (where X is reboot in this case). > > > In this context, note that the poweroff handler patchset is abandoned/dead. > Neither the power maintainers nor Linus liked the idea of having prioritized > poweroff handlers. I hadn't realised that either. Thanks for letting me know. :) > > > Not sure I understand the reference to EFI. Does EFI install a means > > > to restart the system ? > > > > Through EFI runtime services there's a mechanism to reset the machine. > > In certain cases this must be called so as to allow EFI to set things up > > to run after reboot (e.g. capsules for FW updates), while in other cases > > it's perfectly fine to call other mechanisms directly. > > > Sounds like its priority depends on the context. That might be a bit tricky, > but it might be possible if EFI uses the API to register its restart handler > and re-registers itself if needed. Would that make sense ? Sure, I would imagine the EFI code should know when an EFI-handled reboot is necessary. It's not something I've looked into in great detail hwoever, I'm just aware of the general requirement. Thanks, Mark. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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