linux-kernel - Re: Tearing down DMA transfer setup after DMA client has finished

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Message-ID: <yw1xa8c61w88.fsf@unicorn.mansr.com>
Date:   Thu, 08 Dec 2016 11:44:23 +0000
From:   Måns Rullgård <mans@...sr.com>
To:     Vinod Koul <vinod.koul@...el.com>
Cc:     Mason <slash.tmp@...e.fr>, Russell King <linux@....linux.org.uk>,
        dmaengine@...r.kernel.org,
        Linus Walleij <linus.walleij@...aro.org>,
        Dan Williams <dan.j.williams@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Jon Mason <jdmason@...zu.us>, Mark Brown <broonie@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Lee Jones <lee.jones@...aro.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Arnd Bergmann <arnd@...db.de>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Peter Ujfalusi <peter.ujfalusi@...com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Sebastian Frias <sf84@...oste.net>,
        Thibaud Cornic <thibaud_cornic@...madesigns.com>
Subject: Re: Tearing down DMA transfer setup after DMA client has finished

Vinod Koul <vinod.koul@...el.com> writes:

> On Wed, Dec 07, 2016 at 04:44:55PM +0000, Måns Rullgård wrote:
>> Vinod Koul <vinod.koul@...el.com> writes:
>> >> 
>> >> What you're proposing, Vinod, is to make a channel exclusive
>> >> to a driver, as long as the driver has not explicitly released
>> >> the channel, via dma_release_channel(), right?
>> >
>> > Precisely, but yes the downside of that is concurrent access are
>> > limited, but am not sure if driver implements virtual channels and
>> > allows that..
>> 
>> My driver implements virtual channels.  The problem is that the physical
>> dma channels signal completion slightly too soon, at least with
>> mem-to-device transfers.  Apparently we need to keep the sbox routing
>> until the peripheral indicates that it has actually received all the
>> data.
>
> So do we need concurrent accesses by all clients.

Depends on what people do with the chips.

-- 
Måns Rullgård