linux-kernel - Re: [RFC v02 03/15] dmaengine: core: Introduce new, universal API to request a channel

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Date:	Wed, 2 Dec 2015 07:00:05 -0800
From:	Tony Lindgren <tony@...mide.com>
To:	Peter Ujfalusi <peter.ujfalusi@...com>
Cc:	vinod.koul@...el.com, arnd@...db.de, andy.shevchenko@...il.com,
	linux-mmc@...r.kernel.org, nsekhar@...com,
	linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org,
	dmaengine@...r.kernel.org, linux-omap@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC v02 03/15] dmaengine: core: Introduce new, universal API to
 request a channel

* Peter Ujfalusi <peter.ujfalusi@...com> [151202 02:01]:
> On 12/01/2015 07:00 PM, Tony Lindgren wrote:
> >> I see. The dm81xx basically am33xx/am43xx?
> > 
> > Yeah similar to am33xx with different clocks and with a bunch of accelerators.
> > 
> >> Actually I would prefer to use the dmaengine's event router framework and we
> >> do have support for the am33xx/am43xx type of crossbar already implemented.
> >> I'm going to resend the DTS series for am33xx/am43xx to convert them to use
> >> the new DT bindings along with the dma event router support:
> >> https://www.mail-archive.com/linux-omap%40vger.kernel.org/msg120828.html
> > 
> > OK yes a dmaengine event router works too when available. Good to see
> > them as separate driver instances now :) Are only the dts changes missing
> > now?
> > 
> > FYI, when we have separate interconnect driver instances, we don't want to
> > and cannot tweak registers outside the interconnect instance because of them
> > being in separate clock and/or power domains :p
> 
> What does this mean in practice? We can not touch these registers? The DMA
> crossbar is a separate driver from the eDMA driver.

Seem like it should not affect DMA crossbar as it's a separate driver.

What I meant is we need a separate driver for clocks, pinctrl, regulators,
PHY, crossbar or syscon to use the SCM registers from drivers sitting on a
L4 interonnect.

> > In any case, it seems there's no harm using pinctrl for evtmux on dm81xx
> > until the event router is available. It's currently only needed on the
> > t410 emmc that I'm aware of :)
> 
> The AM33xx/AM43xx DMA crossbar support is in 4.4 already:
> 42dbdcc6bf96 dmaengine: ti-dma-crossbar: Add support for crossbar on AM33xx/AM43xx

OK great.

Tony
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