linux-kernel - Re: [PATCH] pcf50633: use a dedicated workqueue for irq processing

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Message-Id: <20090730153425.9a3fc5ac.akpm@linux-foundation.org>
Date:	Thu, 30 Jul 2009 15:34:25 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Paul Fertser <fercerpav@...il.com>
Cc:	sameo@...ux.intel.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pcf50633: use a dedicated workqueue for irq processing

On Tue, 28 Jul 2009 00:41:15 +0400
Paul Fertser <fercerpav@...il.com> wrote:

> Using the default kernel "events" workqueue causes problems with
> synchronous adc readings if initiated from some task on the same
> workqueue.
> 
> I had a deadlock trying to use pcf50633_adc_sync_read from a
> power_supply class driver because the reading was initiated from the
> workqueue and it waited for the irq processing to complete (to get the
> result) and that was put on the same workqueue.

I don't get it.

Do you meant that pcf50633_adc_sync_read() was called via a
schedule_work() handler?  If so, wasn't that a bug?

The patch looks reasonable, but creating yet another kernel thread is a
bit sad.  And I suspect that other MFD drivers are doing the same thing
as pcf50633-core.c, in which case we should change those as well?

So..  please provide a more complete description of the problem which
is being solved so that we can explore alternative fixes.

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