Date: Wed, 7 Dec 2016 22:11:56 +0530
From: Vinod Koul <vinod.koul@intel.com>
To: Mason <slash.tmp@free.fr>
Cc: Mans Rullgard <mans@mansr.com>, Russell King <linux@arm.linux.org.uk>,
        dmaengine@vger.kernel.org, Linus Walleij <linus.walleij@linaro.org>,
        Dan Williams <dan.j.williams@intel.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Jon Mason <jdmason@kudzu.us>, Mark Brown <broonie@kernel.org>,
        Lars-Peter Clausen <lars@metafoo.de>, Lee Jones <lee.jones@linaro.org>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Maxime Ripard <maxime.ripard@free-electrons.com>,
        Dave Jiang <dave.jiang@intel.com>,
        Peter Ujfalusi <peter.ujfalusi@ti.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
        Sebastian Frias <sf84@laposte.net>,
        Thibaud Cornic <thibaud_cornic@sigmadesigns.com>
Subject: Re: Tearing down DMA transfer setup after DMA client has finished
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On Tue, Dec 06, 2016 at 01:42:31PM +0100, Mason wrote:
> On 06/12/2016 06:12, Vinod Koul wrote:
> 
> > On Tue, Nov 29, 2016 at 07:25:02PM +0100, Mason wrote:
> > 
> >> Is there a way to write a driver within the existing framework?
> > 
> > I think so, looking back at comments from Russell, I do tend to agree with
> > that. Is there a specific reason why sbox can't be tied to alloc and free
> > channels?
> 
> Here's a recap of the situation.
> 
> The "SBOX+MBUS" HW is used in several iterations of the tango SoC:

btw is SBOX setup dependent upon the peripheral connected to?

> 
> tango3
>   2 memory channels available
>   6 devices ("clients"?) may request an MBUS channel

But only 2 can get a channel at any time..

> 
> tango4 (one more channel)
>   3 memory channels available
>   7 devices may request an MBUS channel :
>     NFC0, NFC1, SATA0, SATA1, memcpy, (IDE0, IDE1)

Same here

Only thing is users shouldn't hold on to channel and freeup when not in use.

> Notes:
> The current NFC driver supports only one controller.
> IDE is mostly obsolete at this point.
> 
> tango5 (SATA gets own dedicated MBUS channel pair)
>   3 memory channels available
>   5 devices may request an MBUS channel :
>     NFC0, NFC1, memcpy, (IDE0, IDE1)
> 
> 
> If I understand the current DMA driver (written by Mans), client
> drivers are instructed to use a specific channel in the DT, and
> the DMA driver muxes access to that channel. The DMA driver
> manages a per-channel queue of outstanding DMA transfer requests,
> and a new transfer is started friom within the DMA ISR
> (modulo the fact that the interrupt does not signal completion
> of the transfer, as explained else-thread).
> 
> 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..

Thanks
-- 
~Vinod