linux-kernel - Re: [spi-devel-general] adding bits_per_word to struct spi_board_info to mirror struct spi

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Date:	Tue, 08 May 2007 15:31:35 +0800
From:	Bryan WU <bryan.wu@...log.com>
To:	David Brownell <david-b@...bell.net>
Cc:	Mike Frysinger <vapier.adi@...il.com>,
	spi-devel-general@...ts.sourceforge.net,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [spi-devel-general] adding bits_per_word to struct
	spi_board_info to mirror struct spi_device

On Mon, 2007-05-07 at 22:00 -0700, David Brownell wrote:
> On Monday 07 May 2007, Bryan WU wrote:
> 
> > currently, there are some duplicated data members in spi_device struct
> > spi_board_info struct. This two structs are confused driver writers and
> > boards driver users.
> 
> How would that confusion arise?  Only arch/.../board-xxx.c writers
> normally even see spi_board_info; the exception is that someone who
> writes an add-on board -- maybe a USB-to-SPI adapter -- would call the
> rarely used spi_new_device() routine.
> 
> Developers writing a SPI drivers -- controller drivers touching some
> SOC's serial controller hardware, or "struct spi_driver" protocol code
> talking to a chip through such a controller -- never see board info.
> They only see "struct spi_device".  So I don't see why they would have
> a reason to be confused.
> 
> - Dave

Yes, I agree with you.
spi_board_info ---> board writers.
spi_device ---> spi device driver writers.

It is very clear for me, a spi_master driver developer.

But how does a board writer know the capabilities which the target
spi_device driver supports? For example, a board writer use 16
bits_per_word in a spi_board_info, while the spi_device does not support
this. And maybe other special function spi_device driver can provide but
board writer doesn't know or doesn't know how to use this in
spi_board_info.

So can we just use one struct for both board writers and spi device
driver developers?

Thanks
-Bryan Wu

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