linux-kernel - Re: [PATCH 2/4] mtd: sh_flctl: drop unused variable

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Message-ID: <20150504060346.GB26350@opentech.at>
Date:	Mon, 4 May 2015 08:03:46 +0200
From:	Nicholas Mc Guire <der.herr@...r.at>
To:	Vinod Koul <vinod.koul@...el.com>
Cc:	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Nicholas Mc Guire <hofrat@...dl.org>,
	Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Brian Norris <computersforpeace@...il.com>,
	Wolfram Sang <wsa@...-dreams.de>,
	Arnd Bergmann <arnd@...db.de>, linux-mtd@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] mtd: sh_flctl: drop unused variable

On Mon, 04 May 2015, Vinod Koul wrote:

> On Sun, May 03, 2015 at 10:33:43PM +0300, Laurent Pinchart wrote:
> > Hi Nicholas,
> > 
> > Thank you for the patch.
> > 
> > On Saturday 02 May 2015 09:57:08 Nicholas Mc Guire wrote:
> > > shdma_tx_submit() called via dmaengine_submit() returns the assigned
> > > cookie but this is not used here so the variable and assignment can
> > > be dropped.
> > > 
> > > Signed-off-by: Nicholas Mc Guire <hofrat@...dl.org>
> > 
> > I would rephrase the commit message to avoid mentioning shdma_tx_submit() as 
> > that's not relevant. Something like "dmaengine_submit() returns the assigned
> > cookie but this is not used here so the variable and assignment can be 
> > dropped."
> And I am bit surrised about taht. Ideally the driver should use the cookie
> to check the status later on...
>
looking at other drivers it seems like the drivers should call 
dma_submit_error(cookie); on the received cookie - which does:
  return cookie < 0 ? cookie : 0;
but doing that after dmaengine_submit() which actually already queued the
this request in shdma_base.cc:shdma_tx_submit() might not be that helpful 
and looking at dma_cookie_assign() I do not see how the condition that 
dma_submit_error is checking for ever could occur as it can't go below 
cookie = DMA_MIN_COOKIE which is defined to 1 (include/linux/dmaengine.h)

As other drivers seem to not be doing more with the returned cookie than 
calling dma_submit_error() on it this seems ok here ...but I'm not that
deep into this - my starting point was a simple API inconsisteny in the
use of wait_for_completion_timeout() :)

thx!
hofrat
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