Re: [PATCH v1.1 2/2] iio: dac: dac5571: Fix chip id detection for OF devices

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Jonathan,

On Sat, Jul 24, 2021 at 03:43:08PM +0100, Jonathan Cameron wrote:
> On Sat, 24 Jul 2021 03:06:54 +0300 Laurent Pinchart wrote:
> 
> > From: Jose Cazarin <joseespiriki@gmail.com>
> > 
> > When matching an OF device, the match mechanism tries all components of
> > the compatible property. This can result with a device matched with a
> > compatible string that isn't the first in the compatible list. For
> > instance, with a compatible property set to
> > 
> >     compatible = "ti,dac081c081", "ti,dac5571";
> > 
> > the driver will match the second compatible string, as the first one
> > isn't listed in the of_device_id table. The device will however be named
> > "dac081c081" by the I2C core.
> > 
> > This causes an issue when identifying the chip. The probe function
> > receives a i2c_device_id that comes from the module's I2C device ID
> > table. There is no entry in that table for "dac081c081", which results
> > in a NULL pointer passed to the probe function.
> > 
> > To fix this, add chip_id information in the data field of the OF device
> > ID table, and retrieve it with of_device_get_match_data() for OF
> > devices.
> > 
> > Signed-off-by: Jose Cazarin <joseespiriki@gmail.com>
> > Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> 
> Interesting problem that I hadn't previously realised could happen.
> 
> One request though, can we use device_get_match_data() here rather than
> the of specific version?  Include property.h as well for that.
> 
> That should allow the same issue with compatible to work correctly when
> using PRP0001 based ACPI methods. 
> https://elixir.bootlin.com/linux/v5.14-rc1/source/drivers/acpi/bus.c#L891
> Will result in acpi_of_device_get_match_data() being called which will
> match to the of_device_id table.

Good point. I wasn't aware of PRP0001. I'll submit a v2 with this fixed,
after giving a bit of time for additional review, if any (I'm in
particular interested in whether this issue should be fixed in
individual drivers or in the I2C core, as explained in the cover
letter)).

> > ---
> > Changes since v1:
> > 
> > - Include linux/of_device.h
> > ---
> >  drivers/iio/dac/ti-dac5571.c | 28 ++++++++++++++++++----------
> >  1 file changed, 18 insertions(+), 10 deletions(-)
> > 
> > diff --git a/drivers/iio/dac/ti-dac5571.c b/drivers/iio/dac/ti-dac5571.c
> > index 2a5ba1b08a1d..8ceb1b42b14e 100644
> > --- a/drivers/iio/dac/ti-dac5571.c
> > +++ b/drivers/iio/dac/ti-dac5571.c
> > @@ -19,6 +19,7 @@
> >  #include <linux/i2c.h>
> >  #include <linux/module.h>
> >  #include <linux/mod_devicetable.h>
> > +#include <linux/of_device.h>
> >  #include <linux/regulator/consumer.h>
> >  
> >  enum chip_id {
> > @@ -311,6 +312,7 @@ static int dac5571_probe(struct i2c_client *client,
> >  	const struct dac5571_spec *spec;
> >  	struct dac5571_data *data;
> >  	struct iio_dev *indio_dev;
> > +	enum chip_id chip_id;
> >  	int ret, i;
> >  
> >  	indio_dev = devm_iio_device_alloc(dev, sizeof(*data));
> > @@ -326,7 +328,13 @@ static int dac5571_probe(struct i2c_client *client,
> >  	indio_dev->modes = INDIO_DIRECT_MODE;
> >  	indio_dev->channels = dac5571_channels;
> >  
> > -	spec = &dac5571_spec[id->driver_data];
> > +	if (dev->of_node)
> > +		chip_id = (uintptr_t)of_device_get_match_data(dev);
> > +	else
> > +		chip_id = id->driver_data;
> > +
> > +	spec = &dac5571_spec[chip_id];
> > +
> >  	indio_dev->num_channels = spec->num_channels;
> >  	data->spec = spec;
> >  
> > @@ -384,15 +392,15 @@ static int dac5571_remove(struct i2c_client *i2c)
> >  }
> >  
> >  static const struct of_device_id dac5571_of_id[] = {
> > -	{.compatible = "ti,dac5571"},
> > -	{.compatible = "ti,dac6571"},
> > -	{.compatible = "ti,dac7571"},
> > -	{.compatible = "ti,dac5574"},
> > -	{.compatible = "ti,dac6574"},
> > -	{.compatible = "ti,dac7574"},
> > -	{.compatible = "ti,dac5573"},
> > -	{.compatible = "ti,dac6573"},
> > -	{.compatible = "ti,dac7573"},
> > +	{.compatible = "ti,dac5571", .data = (void *)single_8bit},
> > +	{.compatible = "ti,dac6571", .data = (void *)single_10bit},
> > +	{.compatible = "ti,dac7571", .data = (void *)single_12bit},
> > +	{.compatible = "ti,dac5574", .data = (void *)quad_8bit},
> > +	{.compatible = "ti,dac6574", .data = (void *)quad_10bit},
> > +	{.compatible = "ti,dac7574", .data = (void *)quad_12bit},
> > +	{.compatible = "ti,dac5573", .data = (void *)quad_8bit},
> > +	{.compatible = "ti,dac6573", .data = (void *)quad_10bit},
> > +	{.compatible = "ti,dac7573", .data = (void *)quad_12bit},
> >  	{}
> >  };
> >  MODULE_DEVICE_TABLE(of, dac5571_of_id);
> 

-- 
Regards,

Laurent Pinchart