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

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Date:	Mon, 27 Aug 2012 22:58:46 +0800
From:	Hein Tibosch <hein_tibosch@...oo.es>
To:	Hans-Christian Egtvedt <egtvedt@...fundet.no>
CC:	viresh kumar <viresh.kumar@...aro.org>,
	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 8/27/2012 7:14 PM, Hans-Christian Egtvedt wrote:
> Around Mon 27 Aug 2012 16:47:40 +0800 or thereabout, Hein Tibosch wrote:
>> On 8/27/2012 3:03 PM, Hans-Christian Egtvedt wrote:
>>> Brushing up the config items:
>>>
>>> +config DW_DMAC_BIG_ENDIAN_IO
>>> +	bool "Use big endian I/O register access"
>>> +	default y if AVR32
>>> +	depends on DW_DMAC
>>> +	help
>>> +	  Say yes here to use big endian I/O access when reading and writing
>>> +	  to the DMA controller registers. This is needed on some platforms,
>>> +	  like the Atmel AVR32 architecture.
>>> +
>>> +	  If unsure, use the default setting.
> This sounds good in my ears, but I don't speak English natively.
I think you Norwegians are doing very well in English
And btw, I'm not from .es but from .nl, which is very close to England

>> And as I'd like to define the maximum memory transfer width in the same
>> Kconfig:
>>
>> +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?

Hein
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