linux-kernel - Re: CONFIG_DEBUG

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Message-ID: <20150826193820.GT14625@saruman.tx.rr.com>
Date:	Wed, 26 Aug 2015 14:38:20 -0500
From:	Felipe Balbi <balbi@...com>
To:	Ezequiel Garcia <ezequiel@...guardiasur.com.ar>
CC:	Felipe Balbi <balbi@...com>, Ingo Molnar <mingo@...e.hu>,
	Tony Lindgren <tony@...mide.com>,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux ARM Kernel Mailing List 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: CONFIG_DEBUG_SHIRQ and PM

Hi,

On Wed, Aug 26, 2015 at 04:29:52PM -0300, Ezequiel Garcia wrote:
> Felipe,
> 
> On 25 August 2015 at 16:58, Felipe Balbi <balbi@...com> wrote:
> > Hi Ingo,
> >
> > I'm facing an issue with CONFIG_DEBUG_SHIRQ and pm_runtime when using
> > devm_request_*irq().
> >
> 
> I may be jumping on the gun here, but I believe here's your problem.
> Using devm_request_irq with shared IRQs is not a good idea.
> 
> Or at least, it forces you to handle interrupts after your device
> is _completely_ removed (e.g. your IRQ cookie could be bogus).
> 
> AFAICS, the CONFIG_DEBUG_SHIRQ option is just triggering a couple
> spurious interrupts, that are expected to happen anyway.
> 
> Your IRQ is shared, and so you may get any IRQ at any time,
> coming from another device (not yours).
> 
> So, if I'm right, my suggestion is simple: use request_irq/free_irq
> and free your IRQ before you disable your clocks, remove your device,
> etc.

yeah, that's just a workaround though. Specially with IRQ flags coming
from DT, driver might have no knowledge that its IRQ is shared to start
with.

Besides, removing devm_* is just a workaround to the real problem. It
seems, to me at least, that drivers shouldn't be calling
pm_runtime_put_sync(); pm_runtime_disable() from their ->remove(),
rather the bus driver should be responsible for doing so; much
usb_bus_type and pci_bus_type do. Of course, this has the side effect of
requiring buses to make sure that by the time ->probe() is called, that
device's clocks are stable and running and the device is active.

However, that's not done today for the platform_bus_type and, frankly,
that would be somewhat of a complex problem to solve, considering that
different SoCs integrate IPs the way they want.

Personally, I think removing devm_* is but a workaround to the real
thing we're dealing with.

-- 
balbi

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