linux-kernel - Re: [PATCH 1/2] dw_dmac: make driver endianness configurable

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Message-ID: <CAKohpo=ALUNOnQdQjNd1Y2jtocxjixKCiBrRZp8qGErqg1LSKw@mail.gmail.com>
Date:	Tue, 28 Aug 2012 08:53:06 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Hein Tibosch <hein_tibosch@...oo.es>
Cc:	Hans-Christian Egtvedt <egtvedt@...fundet.no>,
	spear-devel <spear-devel@...t.st.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"ludovic.desroches" <ludovic.desroches@...el.com>,
	Havard Skinnemoen <havard@...nnemoen.net>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arnd Bergmann <arnd.bergmann@...aro.org>
Subject: Re: [PATCH 1/2] dw_dmac: make driver endianness configurable

On 27 August 2012 20:28, Hein Tibosch <hein_tibosch@...oo.es> wrote:
>>> +config DW_DMAC_MEM_64_BIT
>>> +    bool "Allow 64-bit memory transfers"
>>> +    default y if !AVR32
>>> +    depends on DW_DMAC
>>> +    help
>>> +      Say yes if the DMA controller may do 64-bit memory transfers
>>> +      For AVR32, say no because only up to 32-bit transfers are
>>> +      defined
>> Is this sane to add? Could some non-AVR32 platforms use 64-bit and 32-bit
>> depending on runtime configuration? E.g. if you build a kernel with support
>> for multiple boards/processors, and there is a mix of 32-bit and 64-bit wide
>> DMA support.
>>
>> I think it is better to select 32/64-bit at runtime.
>
> I did that in the first patch, adding a new property to the dw_dma_slave
> structure. It had the small disadvantage that some arch code had to be
> adapted (at32ap700x.c).
>
> Viresh, what do you think? Add a property called "mem_64_bit_access" or so?
>
> Or should it be passed as a member of 'dw_dma_platform_data', because it
> is a property of the (entire) DMA controller?

I think second option is better. But can there be some supportive scenarios of
first option?

We have a system, with two different memory controllers, one supporting 32 bit
and other 64 bit?

Or what we can do now is: go with option 2, i.e. update dw_dma_platform_data
and if some platform like what i mentioned above comes, then we can move it
to slave data.

viresh
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