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

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Message-ID: <yw1xwpfr7h9y.fsf@unicorn.mansr.com>
Date:   Fri, 25 Nov 2016 14:42:17 +0000
From:   Måns Rullgård <mans@...sr.com>
To:     Mason <slash.tmp@...e.fr>
Cc:     Vinod Koul <vinod.koul@...el.com>, 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>
Subject: Re: Tearing down DMA transfer setup after DMA client has finished

Mason <slash.tmp@...e.fr> writes:

> On 25/11/2016 15:12, Måns Rullgård wrote:
>
>> Mason writes:
>> 
>>> On 25/11/2016 12:57, Måns Rullgård wrote:
>>>
>>>> The same DMA unit is also used for SATA, which is an off the shelf
>>>> Designware controller with an in-kernel driver.  This interrupt timing
>>>> glitch can actually explain some intermittent errors I've observed with
>>>> it.
>>>
>>> FWIW, newer chips embed an AHCI controller, with a dedicated
>>> memory channel.
>>>
>>> FWIW2, the HW dev said memory channels are "almost free", and he
>>> would have no problem giving each device their own private channel
>>> read/write pair.
>> 
>> We still need to deal with the existing hardware.
>
> Can you confirm that your MBUS driver, in its current form,
> does not support memcpy-type transfers, which generate two
> IRQs (one from send agent, one from receive agent)?

It does not.

> Do you plan to support that, or is it just too quirky?

I hadn't planned on doing that, but I'm ruling it out entirely.

-- 
Måns Rullgård