linux-kernel - Re: [PATCH 2/3] dma: add __must_check annotation for dmaengine

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Date:	Fri, 21 Aug 2015 14:02:45 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	peter@...leysoftware.com, Dan Williams <dan.j.williams@...el.com>,
	dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
	nsekhar@...com, linux-omap@...r.kernel.org,
	linux-serial@...r.kernel.org, john.ogness@...utronix.de,
	Peter Ujfalusi <peter.ujfalusi@...com>
Subject: Re: [PATCH 2/3] dma: add __must_check annotation for
 dmaengine_pause()

On Tue, Aug 11, 2015 at 02:34:29PM +0200, Sebastian Andrzej Siewior wrote:
> On 08/11/2015 12:06 PM, Russell King - ARM Linux wrote:
> > I think what people need to learn is that an API in the kernel which
> > returns an int _can_ fail - it returns an int so it _can_ return an
> > error code.  If it _can_ return an error code, there _will_ be
> > implementations which _do_.
> > 
> > If you don't check the return code, either your code doesn't care whether
> > the function was successful or not, or you're playing with fire.  This is
> > a prime example of playing with fire.
> > 
> > Let's leave the crappy userspace laziness with regard to error checking
> > to userspace, and keep it out of the kernel.
> > 
> > Yes, the DMA engine capabilities may not be sufficient to describe every
> > detail of DMA engines, but that's absolutely no reason to skimp on error
> > checking.  Had there been some kind of error checking at the site, this
> > problem would have been spotted before the 8250-omap driver was merged.
> 
> Let me disable RX-DMA in 8250-omap code and push that stable. Then we
> won't need a special annotation for pause support because it remains
> off and is currently about one user. I browsed each driver in
> drivers/dma each one which does support pause supports it and all of
> them implement it unconditionally (ipu_idmac grabs a mutex first but
> this is another story).
> Adding error checking to 8250-omap like I have it in #1 and disabling
> RX-DMA in case pause fails looks be reasonable since there is nothing
> else that can be done I guess.
> Once we have the missing piece in omap-dma the RX-DMA can be enabled in
> 8250-omap.
> Does this sound like a plan we can agree on?

Yes sounds good to me..

-- 
~Vinod
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