linux-kernel - Re: [PATCH v8 3/5] amba: Don't unprepare the clocks if device driver wants IRQ safe runtime PM

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAPDyKFozj54qymGyq1QaOp_gLey4GOKtnAJWek+WfieJ-0gPaw@mail.gmail.com>
Date:	Tue, 4 Nov 2014 10:11:35 +0100
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	Jonathan Corbet <corbet@....net>,
	Dan Williams <dan.j.williams@...el.com>,
	Vinod Koul <vinod.koul@...el.com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	dmaengine@...r.kernel.org, Lars-Peter Clausen <lars@...afoo.de>,
	Michal Simek <michal.simek@...inx.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [PATCH v8 3/5] amba: Don't unprepare the clocks if device driver
 wants IRQ safe runtime PM

On 4 November 2014 02:57, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> On Monday, November 03, 2014 10:41:02 AM Alan Stern wrote:
>> On Mon, 3 Nov 2014, Russell King - ARM Linux wrote:
>>
>> > That makes it pretty horrid from the point of view of having bus
>> > management code, because we now have the management of the bus clock
>> > split between the bus layer and the device driver.
>> >
>> > This is /really/ a problem for runtime PM.  Runtime PM permits there
>> > to be a bus layer involved - and runtime PM can also be coupled up
>> > to PM domains as well.  For all this stuff, the context which the
>> > callbacks are called in depends on whether the driver itself has
>> > marked the device as having IRQ-safe callbacks.
>> >
>> > That's fine, but the bus and PM domain level code then /really/ needs
>> > to know what context they're being called in, so they know whether
>> > they can sleep or not, or they must to be written to always use
>> > non-sleeping functions so they work in both contexts.  If we assume
>> > the former, then that implies that the irq-safe flag must never change
>> > state between a suspend and a resume.
>>
>> If a bus subsystem or PM domain is going to allow its drivers to choose
>> between IRQ-safe and non-IRQ-safe runtime PM, then it is up to the
>> subsystem to come up with a way for drivers to indicate their choice.
>>
>> I tend to agree with Rafael that testing dev->power.irq_safe should be
>> good enough, with no real need for a wrapper.  But the subsystem can
>> use a different mechanism if it wants.
>>
>> Bear in mind, however, that once the irq_safe flag has been set, the
>> runtime PM core offers no way to turn it off again.
>
> There is a problem with it, though.  Say, a driver handles a device that
> may or may not be in a power domain.  Or in other words, the power domain
> the device is in may or may not be always on.  If the domain is always on,
> the runtime PM callbacks are IRQ-safe (they depend on the driver only).
> If it isn't, they may not be IRQ-safe.  How's the driver going to decide
> whether or not to set power.irq_safe?

>From my point of view; the decision whether the driver will set the
IRQ safe flag is in principle a software design choice.

Currently genpd isn't able to power off, if one of its devices are IRQ
safe configured. That's a limitation in genpd which we need to fix and
it's on my TODO list.

My point is thus, I don't think the driver should care about PM
domains at all regarding using the IRQ safe option. Does that make
sense?

Kind regards
Uffe
--
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/