linux-kernel - Re: [PATCH] dmaengine: pxa: handle bus errors

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Message-ID: <20160416051834.GY2274@localhost>
Date:	Sat, 16 Apr 2016 10:48:34 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Robert Jarzmik <robert.jarzmik@...e.fr>
Cc:	Daniel Mack <daniel@...que.org>,
	Haojian Zhuang <haojian.zhuang@...il.com>,
	linux-arm-kernel@...ts.infradead.org, dmaengine@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dmaengine: pxa: handle bus errors

On Thu, Apr 14, 2016 at 08:23:26PM +0200, Robert Jarzmik wrote:
> Vinod Koul <vinod.koul@...el.com> writes:
> 
> > On Mon, Mar 28, 2016 at 11:32:24PM +0200, Robert Jarzmik wrote:
> >> In the current state, upon bus error the driver will spin endlessly,
> >> relaunching the last tx, which will fail again and again :
> >>  - a bus error happens
> >>  - pxad_chan_handler() is called
> >>  - as PXA_DCSR_STOPSTATE is true, the last non-terminated transaction is
> >>    lauched, which is the one triggering the bus error, as it didn't
> >>    terminate
> >>  - moreover, the STOP interrupt fires a new, as the STOPIRQEN is still
> >>    active
> >> 
> >> Break this logic by stopping the automatic relaunch of a dma channel
> >> upon a bus error, even if there are still pending issued requests on it.
> >> 
> >> As dma_cookie_status() seems unable to return DMA_ERROR in its current
> >> form, ie. there seems no way to mark a DMA_ERROR on a per-async-tx
> >> basis, it is chosen in this patch to remember on the channel which
> >> transaction failed, and report it in pxad_tx_status().
> >> 
> >> It's a bit misleading because if T1, T2, T3 and T4 were queued, and T1
> >> was completed while T2 causes a bus error, the status of T3 and T4 will
> >> be reported as DMA_IN_PROGRESS, while the channel is actually stopped.
> >
> > No it is not misleading. The subsequent descriptor can be submitted and
> > continued. But yes you are right on the error reporting part, that is
> > something we need to add.
> Ok, fair enough.
> 
> > So what exactly are you trying to fix/achive here?
> Euh you mean the first chapter about the "endless spin" is not clear ?
> This is what I'm trying to fix, the unstoppable endless relauch of a descriptor
> doomed to make the same bus error over and over again.

Okay so IIUC the patch here essential stops all transfers and abort the
channel, right?

-- 
~Vinod