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

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Date:   Tue, 9 Oct 2018 12:05:22 +0200
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Chuanhua Han <chuanhua.han@....com>
Cc:     "broonie@...nel.org" <broonie@...nel.org>,
        "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, 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.

> 2. As I understand, bits_per_word does not
> exist for non-byte alignment, but for the need to reserve non-byte
> transmission mode that meets the controller.

Exactly. It's an optimization you have to take care of inside your
driver. The core cannot help you with that.

> 3. In addition, now the
> XSPI of dspi cannot transfer data normally, so this problem needs to
> be solved.

I still don't understand what the problem is.

> As for the DMA transfer mode, some colleagues will study
> it.