linux-kernel - Re: [PATCH] [RFC] Xilinx MPMC SDMA subsystem

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Date:	Mon, 29 Mar 2010 14:20:31 -0600
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Sergey Temerkhanov <temerkhanov@...dex.ru>
Cc:	linuxppc-dev@...ts.ozlabs.org, steve@...idescorp.com,
	microblaze-uclinux@...e.uq.edu.au,
	Sergey Temerkhanov <temerkhanov@...ronik.ru>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] [RFC] Xilinx MPMC SDMA subsystem

On Mon, Mar 29, 2010 at 1:04 PM, Sergey Temerkhanov
<temerkhanov@...dex.ru> wrote:
> On Monday 29 March 2010 19:56:15 Grant Likely wrote:
>> On Mon, Mar 29, 2010 at 9:42 AM, Steven J. Magnani
>>
>> <steve@...idescorp.com> wrote:
>> > On Fri, 2010-03-26 at 17:53 -0600, Grant Likely wrote:
>> >> I've not got time to review this patch right now, but Sergey and
>> >> Steven, you both posted MPMC drivers on the same day; Steven on the
>> >> microblaze list and Sergey on the powerpc list.  Can you two please
>> >> coordinate and figure out how to mork toward a single driver that will
>> >> meet both your needs?  I don't want to have 2 drivers (3 if you count
>> >> the ll_temac driver) in mainline for the same hardware interface.
>> >
>> > I don't think we'll end up with a single driver. A MPMC DMA Engine
>> > driver is useful only on "loopback" SDMA ports. Sergey's code looks like
>> > a nice generic interface to Xilinx SDMA HW that could be used by the
>> > xlldma and ll_temac drivers, for instance. Both of those will get
>> > smaller, but won't go away.
>
> Yes, it's like having IBM EMAC driver and MAL layer or something
>
>> >
>> > For this to be useful to me, it would need to be located somewhere more
>> > accessible than arch/powerpc and it would need to have initialization
>> > methods that don't depend on OF. In my build I would have platform code
>> > that binds to the xlldma platform attachment, which would call Sergey's
>> > SDMA code to assign it the proper resources.
>>
>> That should be fine.
>
> Well, I'll look at my old code for the platform interface bindings. I remember
> it worked well on arch/ppc with my other drivers.

Don't get too caught up in this aspect.  of_platform_bus_type is being
merged with platform_bus_type.  One driver can be written to handle
both use cases.  However, it may not make any sense for the DMA
library layer to have a bus binding since it is mostly a set of shared
routines.  I'm fine if the bindings are only at the SDMA driver and
ll_temac driver level.

g.

-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.
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