linux-kernel - Re: [PATCH] iio: accel: bmc150: Add OF device ID table

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Date:   Sun, 10 Dec 2017 16:12:23 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Javier Martinez Canillas <javierm@...hat.com>
Cc:     Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Hans de Goede <hdegoede@...hat.com>,
        linux-kernel@...r.kernel.org, Hartmut Knaack <knaack.h@....de>,
        linux-iio@...r.kernel.org, Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        devicetree@...r.kernel.org, Wolfram Sang <wsa@...-dreams.de>
Subject: Re: [PATCH] iio: accel: bmc150: Add OF device ID table

On Mon, 4 Dec 2017 11:24:40 +0100
Javier Martinez Canillas <javierm@...hat.com> wrote:

> Hello Jonathan,
> 
> On 12/04/2017 10:44 AM, Jonathan Cameron wrote:
> > On Mon, 4 Dec 2017 09:29:38 +0100
> > Hans de Goede <hdegoede@...hat.com> wrote:
> >   
> >> Hi,
> >>
> >> On 01-12-17 12:10, Javier Martinez Canillas wrote:  
> >>> The driver doesn't have a struct of_device_id table but supported devices
> >>> are registered via Device Trees. This is working on the assumption that a
> >>> I2C device registered via OF will always match a legacy I2C device ID and
> >>> that the MODALIAS reported will always be of the form i2c:<device>.
> >>>
> >>> But this could change in the future so the correct approach is to have an
> >>> OF device ID table if the devices are registered via OF.
> >>>
> >>> The I2C device ID table entries have the .driver_data field set, but they
> >>> are not used in the driver so weren't set in the OF device table entries.
> >>>
> >>> Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>
> >>> ---
> >>>
> >>>   drivers/iio/accel/bmc150-accel-i2c.c | 12 ++++++++++++
> >>>   1 file changed, 12 insertions(+)
> >>>
> >>> diff --git a/drivers/iio/accel/bmc150-accel-i2c.c b/drivers/iio/accel/bmc150-accel-i2c.c
> >>> index f85014fbaa12..8ffc308d5fd0 100644
> >>> --- a/drivers/iio/accel/bmc150-accel-i2c.c
> >>> +++ b/drivers/iio/accel/bmc150-accel-i2c.c
> >>> @@ -81,9 +81,21 @@ static const struct i2c_device_id bmc150_accel_id[] = {
> >>>   
> >>>   MODULE_DEVICE_TABLE(i2c, bmc150_accel_id);
> >>>   
> >>> +static const struct of_device_id bmc150_accel_of_match[] = {
> >>> +	{ .compatible = "bosch,bmc150_accel" },
> >>> +	{ .compatible = "bosch,bmi055_accel" },    
> >>
> >> These look a bit weird, there is no reason to mirror the i2c_device_ids  
> > 
> > There has been a steady move for a long time to add these IDs with the plan
> > that we would stop automatically matching against the manufacturer free
> > i2c IDs. Mostly on the basis that was a hack that brought a lot  
> 
> Matching using OF IDs have been working for some time (since v4.10 AFAICT)
> after the following commit:
> 
> da10c06a044b ("i2c: Make I2C ID tables non-mandatory for DT'ed devices").
> 
> The only remaining problem is with module auto-loading.
> 
> > of effectively unreviewed device tree bindings. As I understand it the
> > eventual plan is to be able to get rid of that old path entirely...
> > +CC Wolfram to see what his view is on this.
> >  
> 
> I don't think we can get rid of the old path entirely since are valid use cases
> for it. For example when the I2C devices are registered with the i2c_new_device
> interface where the bus and address are declared in a struct i2c_board_info (ie:
> old platforms that still use board files or devices with an embedded I2C chip).

Agreed. I only meant the use of that path when matching device tree IDs.
There are still reasons to use it otherwise - including the ones you mention
and indeed manually adding the device - commonly done with various sensors
supported by lm-sensors on x86 boards.   These are often not described in
any way at all.

> 
> What I think though is that drivers should only be required to define the device
> table for the firmware interface used to instantiate them. For example, a driver
> for a device that's DT-only should only have an OF device ID table just like a
> driver for an ACPI-only device only requires to have an ACPI ID table.
> 
> Conversely, a driver for a device that's only instantiated using platform data
> should only have an I2C device ID table.
> 

A lot of drivers are used on both ACPI and DT platforms.  For newer cases we
perhaps don't need the i2c table.


> If a driver supports both DT and legacy platforms, then it's OK to have both ID
> tables defined. What is not correct is to require OF-only drivers to have an I2C
> device ID table just as a workaround to have their modules auto-loading working.

Absolutely agree.

Jonathan
> 
> Best regards,