linux-kernel - Re: [RFC PATCH v2 1/2] amba: Allow AMBA drivers to use their own runtime PM

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Message-ID: <20140912151352.GK12361@n2100.arm.linux.org.uk>
Date:	Fri, 12 Sep 2014 16:13:52 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
Cc:	Dan Williams <dan.j.williams@...el.com>,
	Vinod Koul <vinod.koul@...el.com>,
	linux-kernel@...r.kernel.org, dmaengine@...r.kernel.org,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Grant Likely <grant.likely@...aro.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: [RFC PATCH v2 1/2] amba: Allow AMBA drivers to use their own
	runtime PM

On Fri, Sep 12, 2014 at 04:56:18PM +0200, Krzysztof Kozlowski wrote:
> The AMBA bus driver defines runtime Power Management functions which
> disable and unprepare AMBA bus clock. This is problematic for runtime PM
> because unpreparing a clock might sleep so it is not interrupt safe.
> 
> However some drivers may want to implement runtime PM functions in
> interrupt-safe way (see pm_runtime_irq_safe()). If such driver
> implements its own runtime PM functions then assume it will handle the
> runtime PM completely and it will replace our clock handling.
> 
> Signed-off-by: Krzysztof Kozlowski <k.kozlowski@...sung.com>

Actually, I'd rather just revert 5303c0f46c8708fff4148ebcc491f78710356952
which is clearly the wrong thing to do when we have non-IRQ safe runtime
PM.

What we /could/ do instead is to check whether irq_safe is set after
probe, record that, and then select whether to use the prepare/unprepare
methods based on that.  (Drivers should never dynamically change this.)

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