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

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Message-ID: <20120827111431.GA27868@samfundet.no>
Date:	Mon, 27 Aug 2012 13:14:31 +0200
From:	Hans-Christian Egtvedt <egtvedt@...fundet.no>
To:	Hein Tibosch <hein_tibosch@...oo.es>
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

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:
>> I think the English in kconfig could use some brushing up.
>>  
>>> +config DW_DMAC_BE
>>
>>
>> This name isn't that long, so we could skip the abbreviation of big endian;
>> DW_DMAC_BIG_ENDIAN_IO or something similar?
>>
>>> +	bool "Synopsys DesignWare AHB DMA needs big endian access"
>>>
>> bool "Use big endian I/O register access"
> 
> 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.

> 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.

-- 
mvh
Hans-Christian Egtvedt
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