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

From: Uwe Kleine-König
Date: Fri Nov 19 2021 - 02:40:28 EST

On Thu, Nov 18, 2021 at 06:21:27PM +0000, Mark Brown wrote:
> 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).

It affects c) only if the device tree has a device with compatible =
"spidev". For such a device the history is:

- Before 956b200a846e ("spi: spidev: Warn loudly if instantiated from
DT as "spidev"") in v4.1-rc1:
Just bound silently

- After 956b200a846e up to 6840615f85f6 ("spi: spidev: Add SPI ID
table") in v5.15-rc6:
The device was automatically bound with a warning

- After 6840615f85f6:
The device doesn't bind automatically, when using driver_override
you get a warning.

- With the proposed patch:
The device cannot be bound even using driver_override

Not this affects also devices that use

compatible = "myvender,devicename", "spidev";


Best regards

Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | |

Attachment: signature.asc
Description: PGP signature