linux-kernel - Re: [PATCH 2/2] spi/pxa2xx: use a flag to check if the device is runtime suspended

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Message-ID: <20130619093938.GT1403@sirena.org.uk>
Date:	Wed, 19 Jun 2013 10:39:38 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	linux-kernel@...r.kernel.org, Eric Miao <eric.y.miao@...il.com>,
	Haojian Zhuang <haojian.zhuang@...il.com>,
	Grant Likely <grant.likely@...aro.org>
Subject: Re: [PATCH 2/2] spi/pxa2xx: use a flag to check if the device is
 runtime suspended

On Wed, Jun 19, 2013 at 10:25:08AM +0100, Russell King - ARM Linux wrote:
> On Tue, Jun 18, 2013 at 07:09:48PM +0100, Mark Brown wrote:

> > This sounds like a problem which will affect a lot of devices and hence
> > ought to be handled better by the PM core or at least frameworks in
> > general.  Is it really device specific?

> It's always been something that has been recommended to be dealt with
> by the driver.  If reading the interrupt status you read ~0, then it
> likely is because the device is powered down or removed from the system.

> PCMCIA drivers have done this for years.

I know, some PCI devices too.  It's not just an issue for memory mapped
devices, the same thing happens with devices on other buses - there's a
whole bunch of issues around moving out of the various suspend states
and getting interrupts (things like getting an interrupt controller
waking up and delivering interrupts before the control bus for a device
connected to it has woken up).  

The driver does need to be the one deciding what to do about being in
suspend but we really ought to be able to do something without having to
interact with the hardware partly just for neatness but more because on
general buses the error handling is too painful.

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