linux-kernel - Re: [PATCH 1/7] dmaengine: edma: fix two faults which happen with the 8250

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Date:	Thu, 31 Jul 2014 17:47:02 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	tony@...mide.com, balbi@...com, Joel Fernandes <joelf@...com>,
	Dan Williams <dan.j.williams@...el.com>,
	dmaengine@...r.kernel.org
Subject: Re: [PATCH 1/7] dmaengine: edma: fix two faults which happen with
 the 8250_dma user

On Tue, Jul 29, 2014 at 08:58:58PM +0200, Sebastian Andrzej Siewior wrote:
> The rx path of the 8250_dma user in the RX-timeout case:
> - it starts the RX transfer
> - if the rx-timeout interrupt occures, it dmaengine_pause() the transfer
> - step two is dmaengine_terminate_all() on this channel.
Okay after this whole channel needs to be reset, which means all the
descriptors are discared.
> - based on dmaengine_tx_status() it learns the number of transfered
>   bytes.
> - the rx interrupt occures,
why, channel is terminated, so existing txn needs to be aborted too

>   it does not start the RX-transfer because
>   according to dmaengine_tx_status() the status of the current transfer
>   is still DMA_IN_PROGRESS because the earlier dmaengine_terminate_all()
>   did not reset this.
there is no current transfer anymore

> - on rx-timeout it invokes dmaengine_pause() again. This time, it
>   segfaults because the channel has no descriptor yet.
> 
> To make the upper case work better, this patch adds dma_cookie_complete()
> to complete the cookie. Also it adds is an additional check for echan->edesc
> in case the channel has no descriptor assigned.
I think we are fixing the behvaiour rather than cause. terminate_all(()
needs to do a proper cleanup of the channel

And this looks a series, without cover letter sent to all. Which makes it a
bit hard to see what is getting done

-- 
~Vinod
> 
> Cc: Joel Fernandes <joelf@...com>
> Cc: Vinod Koul <vinod.koul@...el.com>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: dmaengine@...r.kernel.org
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---
>  drivers/dma/edma.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/dma/edma.c b/drivers/dma/edma.c
> index d08c4de..ff05dd4 100644
> --- a/drivers/dma/edma.c
> +++ b/drivers/dma/edma.c
> @@ -256,6 +256,7 @@ static int edma_terminate_all(struct edma_chan *echan)
>  	 * echan->edesc is NULL and exit.)
>  	 */
>  	if (echan->edesc) {
> +		dma_cookie_complete(&echan->edesc->vdesc.tx);
>  		echan->edesc = NULL;
>  		edma_stop(echan->ch_num);
>  	}
> @@ -282,7 +283,7 @@ static int edma_slave_config(struct edma_chan *echan,
>  static int edma_dma_pause(struct edma_chan *echan)
>  {
>  	/* Pause/Resume only allowed with cyclic mode */
> -	if (!echan->edesc->cyclic)
> +	if (!echan->edesc || !echan->edesc->cyclic)
>  		return -EINVAL;
>  
>  	edma_pause(echan->ch_num);
> -- 
> 2.0.1
> 

-- 
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