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

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Date:	Fri, 8 Aug 2014 18:29:50 +0200
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Vinod Koul <vinod.koul@...el.com>
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

* Vinod Koul | 2014-07-31 17:47:02 [+0530]:

>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.

>> 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

In case you are not ignoring me but $reason here is an example that does
not work (with both drivers);

    desc = dmaengine_prep_slave_single(rxchan, …);
    rx_cookie = dmaengine_submit(desc);
    dma_async_issue_pending(rxchan);

    ssleep(2);
    /* Now assume that the transfer did not start */
    st = dmaengine_tx_status(rxchan, rx_cookie, NULL);
    /* st is now DMA_IN_PROGRESS as expected */

    dmaengine_terminate_all(rxchan);
    st = dmaengine_tx_status(rxchan, rx_cookie, NULL);
    /* st is still DMA_IN_PROGRESS but _I_ expect DMA_COMPLETE because
     * it has been terminated / canceled
     */

Both dma driver clean up all / terminate all descriptors as required but
_none_ of them completes the cookie. As a result dma_cookie_status()
still thinks that the transfer is in progress.

Sebastian
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