linux-kernel - Re: [PATCH] spi: Add spi-bits-per-word binding.

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Message-ID: <20170221190830.xyubgimyc2w5p5v6@sirena.org.uk>
Date:   Tue, 21 Feb 2017 11:08:30 -0800
From:   Mark Brown <broonie@...nel.org>
To:     Adrian Fiergolski <adrian.fiergolski@...n.ch>
Cc:     linux-spi@...r.kernel.org, robh+dt@...nel.org,
        mark.rutland@....com, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, miguel.ojeda.sandonis@...il.com
Subject: Re: [PATCH] spi: Add spi-bits-per-word binding.

On Mon, Feb 20, 2017 at 04:35:12PM +0100, Adrian Fiergolski wrote:
> If an SPI controller doesn't support 8 bit transfers
> (master->bits_per_word_mask), it will be never registered (tested with
> spidev):
> of_register_spi_device calls spi_add_device which calls spi_setup. The last
> takes as an argument spi_device struct, which, in case of spidev, has
> bits_per_word set to 0. Thus, the spi_setup function will set it to default
> 8. Further, the same function will call __spi_validate_bits_per_word which
> will fail the whole registration for controllers not supporting 8 bit
> transfers (i.e. xilinx-spi).

This doens't make much sense, if a device driver requires a given number
of bits per word forcing a different value via device tree is not going
to result in the driver actually working.  If you want to use a device
with a controller with restricted bits per word support you need to
change the device driver to support the limited capabilities of the
controller.

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