linux-kernel - Re: [PATCH] ARM: OMAP2+: omap_device: add fail hook for runtime

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Date:	Mon, 09 Dec 2013 08:06:29 -0800
From:	Kevin Hilman <khilman@...aro.org>
To:	Tony Lindgren <tony@...mide.com>
Cc:	Nishanth Menon <nm@...com>, linux-omap@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Tobias Jakobi <tjakobi@...h.uni-bielefeld.de>,
	Joel F <joelf@...com>
Subject: Re: [PATCH] ARM: OMAP2+: omap_device: add fail hook for runtime_pm when bad data is detected

Tony Lindgren <tony@...mide.com> writes:

> * Nishanth Menon <nm@...com> [131203 17:40]:
>> Due to the cross dependencies between hwmod for automanaged device
>> information for OMAP and dts node definitions, we can run into scenarios
>> where the dts node is defined, however it's hwmod entry is yet to be
>> added. In these cases:
>> a) omap_device does not register a pm_domain (since it cannot find
>>    hwmod entry).
>> b) driver does not know about (a), does a pm_runtime_get_sync which
>>    never fails
>> c) It then tries to do some operation on the device (such as read the
>>   revision register (as part of probe) without clock or adequate OMAP
>>   generic PM operation performed for enabling the module.
>> 
>> This causes a crash such as that reported in:
>> https://bugzilla.kernel.org/show_bug.cgi?id=66441
>> 
>> When 'ti,hwmod' is provided in dt node, it is expected that the device
>> will not function without the OMAP's power automanagement. Hence, when
>> we hit a fail condition (due to hwmod entries not present or other
>> similar scenario), fail at pm_domain level due to lack of data, provide
>> enough information for it to be fixed, however, it allows for the driver
>> to take appropriate measures to prevent crash.
>
> Kevin, any comments on this one?

Looks like a good approach to catch these corner cases.

Acked-by: Kevin Hilman <khilman@...aro.org>
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