linux-kernel - Re: [PATCH v6] spi: Add SPI driver for Mikrotik RB4xx series boards

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Message-ID: <20150409215047.GE6023@sirena.org.uk>
Date:	Thu, 9 Apr 2015 22:50:47 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Bert Vermeulen <bert@...t.com>
Cc:	ralf@...ux-mips.org, linux-mips@...ux-mips.org,
	linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org,
	andy.shevchenko@...il.com, jogo@...nwrt.org
Subject: Re: [PATCH v6] spi: Add SPI driver for Mikrotik RB4xx series boards

On Thu, Apr 09, 2015 at 11:31:12PM +0200, Bert Vermeulen wrote:
> On 04/06/2015 06:39 PM, Mark Brown wrote:> On Mon, Apr 06, 2015 at

> > I queried this on a previous version and asked for the code to be better
> > documented...

> I documented it in the commit message:

I'm asking for the *code* to be better documented.  Right now it's just
raising obvious questions which are at best going to cost people time
digging for the reasons.

>  The m25p80-compatible boot flash and (some models) MMC use regular SPI,
>  bitbanged as required by the SoC. However the SPI-connected CPLD has
>  a "fast write" mode, in which two bits are transferred by SPI clock
>  cycle. The second bit is transmitted with the SoC's CS2 pin.

>  Protocol drivers using this fast write facility signal this by setting
>  the cs_change flag on transfers.

> The cs_change flag is used here instead of the openwrt version's
> spi_transfer.fast_write flag. The CPLD driver sets this flag on a
> per-transfer basis.

No, this is broken - it's abusing a standard API in a way that's
completly incompatible with the meaning of that API which is obviously a
very bad idea, especially since good practice is to offload the
implementation of that standard API to the core.  It *sounds* like
you're just trying to implement two wire mode which does have a standard
API, please use that.

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