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

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Date:   Fri, 25 Nov 2016 15:28:39 +0000
From:   Måns Rullgård <mans@...sr.com>
To:     Mason <slash.tmp@...e.fr>
Cc:     Russell King - ARM Linux <linux@...linux.org.uk>,
        Vinod Koul <vinod.koul@...el.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Dave Jiang <dave.jiang@...el.com>,
        Arnd Bergmann <arnd@...db.de>, Mark Brown <broonie@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        dmaengine@...r.kernel.org, Dan Williams <dan.j.williams@...el.com>,
        Jon Mason <jdmason@...zu.us>, Lee Jones <lee.jones@...aro.org>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: Tearing down DMA transfer setup after DMA client has finished

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

> On 25/11/2016 16:12, Måns Rullgård wrote:
>
>> Mason writes:
>> 
>>> I've had several talks with the HW dev, and I don't think they
>>> anticipated the need to mux the 3 channels. In their minds,
>>> customers would choose at most 3 devices to support, and
>>> assign one channel to each device statically.
>>>
>>> In fact, in tango4, supported devices are:
>>> A) NAND Flash controllers 0 and 1
>>> NB: the upstream driver only uses controller 0
>>> B) IDE or SATA controllers 0 and 1
>>> C) a few crypto HW blocks which do not work as expected (unused)
>>>
>>> Customers typically use 1 channel for NAND, maybe 1 for SATA,
>>> and 1 channel remains unused.
>> 
>> The hardware has two sata controllers, and I have a board that uses both.
>
> I don't have the tango3 client devices in mind, but
> 1 NAND + 2 SATA works out alright for 3 channels, right?

There are only two usable channels.

Besides, your 3.4 kernel allocates the channels dynamically, sort of,
but since it has a completely custom api, this particular timing issue
doesn't arise there.

-- 
Måns Rullgård