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 12:00:42 +0200
From:	Peter Ujfalusi <peter.ujfalusi@...com>
To:	Tony Lindgren <tony@...mide.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

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.

> 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

-- 
Péter
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