linux-kernel - Re: [PATCH 1/2] spi: spi-mem: Add the spi_set_xfer

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Message-ID: <20181009103328.GA20774@sirena.org.uk>
Date:   Tue, 9 Oct 2018 11:33:28 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Boris Brezillon <boris.brezillon@...tlin.com>
Cc:     Chuanhua Han <chuanhua.han@....com>,
        "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "eha@...f.com" <eha@...f.com>
Subject: Re: [PATCH 1/2] spi: spi-mem: Add the spi_set_xfer_bpw function

On Tue, Oct 09, 2018 at 12:05:22PM +0200, Boris Brezillon wrote:
> On Tue, 9 Oct 2018 09:52:23 +0000
> Chuanhua Han <chuanhua.han@....com> wrote:

> > 1. In the dspi driver (spi controller), bits_per_word
> > (dspi->bits_per_word = transfer->bits_per_word) passed from the upper
> > layer (spi-mem.c) is used. In this way, I can only assign the
> > appropriate value of transfer->bits_per_word before passing to the
> > controller, that is, the controller driver does not know the value of
> > bits_per_word, and it will use this value when the upper level sets
> > what value is passed.

> I think you're missing my point: ->bits_per_word is not what you're
> looking for if what you're trying to do is use 32-bits accesses when
> things are properly aligned.

To be clear: bits_per_word affects what goes out on the SPI bus (4 byte
words swapped to be in MSB first order), it needn't have any effect on
on what goes on inside the SoC - many controllers fill their FIFO in 32
bit blocks even when sending 8 bit SPI words.

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