linux-kernel - Re: [PATCH] spidev: Make probe to fail early if a spidev compatible is used

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Date:   Thu, 18 Nov 2021 18:21:27 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
Cc:     Javier Martinez Canillas <javierm@...hat.com>,
        linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org,
        kernel@...gutronix.de
Subject: Re: [PATCH] spidev: Make probe to fail early if a spidev compatible
 is used

On Wed, Nov 10, 2021 at 08:42:47AM +0100, Uwe Kleine-König wrote:

> Up to 6840615f85f6 the choices you had to use the spidev driver were
> (assuing a dt machine):

>  a) Use compatible = "spidev" and ignore the warning
>  b) Use compatible = $chipname and add $chipname to the list of
>     supported devices for the spidev driver. (e.g. "rohm,dh2228fv")
>  c) Use compatible = $chipname and force binding the spidev driver using

>    	echo spidev > /sys/bus/spi/devices/spiX.Y/driver_override
> 	echo spiX.Y > /sys/bus/spi/drivers/spidev/bind

> Commit 6840615f85f6 changed that in situation a) you had to switch to c)
> (well, or b) adding "spidev" to the spi id list).

> With the change introduced by this patch, you make it impossible to bind
> the spidev driver to such a device (without kernel source changes) even
> using approach c). I wonder if this is too harsh given that changing the
> dtb is difficult on some machines.

Following up from discussion on IRC: it's not clear to me how option c
is affected?  The change only causes an error if of_device_is_compatible()
is true and driver_override works with spi_device_id not compatibles (I
didn't actually test, in the middle of some other stuff right now).

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