linux-kernel - Re: [PATCH 2/2] DMAENGINE: driver for the ARM PL080/PL081 PrimeCells

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Date:	Thu, 29 Jul 2010 01:12:48 +0200
From:	Linus Walleij <linus.ml.walleij@...il.com>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	yuanyabin1978@...a.com, Peter Pearse <peter.pearse@....com>,
	Ben Dooks <ben-linux@...ff.org>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Alessandro Rubini <rubini@...pv.it>,
	Viresh Kumar <viresh.kumar@...com>,
	Russell King <rmk@....linux.org.uk>
Subject: Re: [PATCH 2/2] DMAENGINE: driver for the ARM PL080/PL081 PrimeCells

2010/7/28 Dan Williams <dan.j.williams@...el.com>:
> On Tue, Jun 29, 2010 at 4:36 AM, Linus Walleij
> <linus.walleij@...ricsson.com> wrote:
>> This creates a DMAengine driver for the ARM PL080/PL081 PrimeCells
>> based on the implementation earlier submitted by Peter Pearse.
>> This is working like a charm for memcpy and slave DMA to the PL011
>> PrimeCell on the PB11MPCore.
>
> Russell I am assuming this implementation and testing is sufficient to
> allay your prior nak [1]?  Linus is oversubscribing virtual channels
> to physical channels to handle muxing.

I don't think Russell has ever NAK:ed the PL08x driver(s). The NAK
was about the PrimeCell DMA extenstions to amba-pl011.c etc.
(Still I'm happy if Russell looks at this thing of course.)

This patch along with the generic channel control removed the
cross-dependency between the PrimeCell DMA patchset and the
drivers/dma DMA engine framework (yay!) so there is no arch/arm
or AMBA stuff involved anymore, other than the fact that this driver
sits on the AMBA/PrimeCell bus.

>> +#ifdef MODULE
>> +
>> +# error "AMBA PL08X DMA CANNOT BE COMPILED AS A LOADABLE MODULE AT PRESENT"
>> +
>> +/*
>> +       a) Some devices might make use of DMA during boot
>> +          (esp true for DMAENGINE implementation)
>> +       b) Memory allocation will need much more attention
>> +          before load/unload can be supported
>> + */
>> +#endif
>
> This is taken care of by being "config bool", but I assume you want
> this for documentation purposes?

Peter had that in and I didn't remove it. If you don't like it you
can remove it or I can send a new patch.

>> +       txd = kzalloc(sizeof(struct pl08x_txd), GFP_KERNEL);
>
> ...appears in the prep routines.  Will this driver be used by any
> storage controllers on the platfom?  Might we deadlock waiting on i/o
> that needs to allocate a descriptor to complete?

I haven't noticed anything but a descriptor pool is on my
list of things to look into and fix.

Yours,
Linus Walleij
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