linux-kernel - Re: [PATCH 6/6] dma/imx-sdma: check whether event_id0 < 32 when set event

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Message-ID: <20120111133458.GD20968@S2101-09.ap.freescale.net>
Date:	Wed, 11 Jan 2012 21:35:00 +0800
From:	Shawn Guo <shawn.guo@...aro.org>
To:	Richard Zhao <richard.zhao@...escale.com>
Cc:	Eric Miao <eric.miao@...aro.org>, patches@...aro.org,
	vinod.koul@...el.com, linux-kernel@...r.kernel.org,
	kernel@...gutronix.de, dan.j.williams@...el.com,
	Richard Zhao <richard.zhao@...aro.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 6/6] dma/imx-sdma: check whether event_id0 < 32 when set
 event_mask

On Wed, Jan 11, 2012 at 09:09:11PM +0800, Richard Zhao wrote:
> On Wed, Jan 11, 2012 at 09:16:17PM +0800, Shawn Guo wrote:
> > On Wed, Jan 11, 2012 at 02:37:08PM +0800, Eric Miao wrote:
> > > I think Richard has made the issue quite clear here, the original
> > 
> > Yes, he has made it clear, but only after I asked for more comments,
> > not with the empty commit message.
> > 
> > > code does seem to have some problems even to me, who do not
> > > understand the very details of the SDMA:
> > > 
> > > -                       sdmac->event_mask0 = 1 << sdmac->event_id0;
> > > -                       sdmac->event_mask1 = 1 << (sdmac->event_id0 - 32);
> > > 
> > > 1. if sdmac->event_id0 >= 32, which will cause event_mask0 to be incorrect
> > > 2. if sdmac->event_id < 32, sdmac->event_mask1 will be incorrect
> > > 
> > My testing tells this is not the case.  The event_mask0 will be 0 in
> > case 1) and event_mask1 will be 0 in case 2), which is quite what we
> > expect.  And I do not believe you will see any functionality bug with
> > the existing code.
> Please see my mail mentioned "we shoud not let it depends on gcc's
> behavior."

In this case, I would rather believe that the author is smart enough
to write the code intentionally based on his good understanding on
behavior of arm-gcc.

-- 
Regards,
Shawn
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