Re: [PATCH v1 2/3] auxdisplay: ht16k33: Make use of device_get_match_data()

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Wed, Feb 22, 2023 at 05:46:00PM +0100, Robin van der Gracht wrote:
> On 2023-02-21 18:48, Andy Shevchenko wrote:
> > On Tue, Feb 21, 2023 at 05:10:00PM +0100, Robin van der Gracht wrote:
> > > On 2023-02-21 14:40, Andy Shevchenko wrote:
> > > > On Tue, Feb 21, 2023 at 03:33:06PM +0200, Andy Shevchenko wrote:

...

> > > > > -	id = i2c_of_match_device(dev->driver->of_match_table, client);
> > > > > -	if (id)
> > > > > -		priv->type = (uintptr_t)id->data;
> > > > > +	priv->type = (uintptr_t)device_get_match_data(dev);
> > > >
> > > > Looking closer the I²C ID table should provide DISP_MATRIX to keep
> > > > default and

> > > > this needs to be not dropped.

^^^^^ (1)

> > > > So, the question is what to do with unknown type then, return -EINVAL
> > > > from probe()?
> > > 
> > > If you leave out your addition of the DISP_UNKNOWN type, the default
> > > type
> > > will be DISP_MATRIX if no match is found, which is as it is now.
> > > 
> > > In that case the following change should suffice:
> > > 
> > > @@ -713,7 +715,6 @@ static int ht16k33_seg_probe(struct device *dev,
> > > struct
> > > ht16k33_priv *priv,
> > >  static int ht16k33_probe(struct i2c_client *client)
> > >  {
> > >      struct device *dev = &client->dev;
> > > -    const struct of_device_id *id;
> > >      struct ht16k33_priv *priv;
> > >      uint32_t dft_brightness;
> > >      int err;
> > > @@ -728,9 +729,8 @@ static int ht16k33_probe(struct i2c_client
> > > *client)
> > >          return -ENOMEM;
> > > 
> > >      priv->client = client;
> > > -    id = i2c_of_match_device(dev->driver->of_match_table, client);
> > > -    if (id)
> > > -        priv->type = (uintptr_t)id->data;
> > > +    priv->type = (uintptr_t)device_get_match_data(dev);
> > > +
> > >      i2c_set_clientdata(client, priv);
> > > 
> > >      err = ht16k33_initialize(priv);
> > > 
> > > Or do you think falling back to DISP_MATRIX if no match is found is
> > > wrong?
> > 
> > First of all, the I²C ID table should actually use DISP_MATRIX.
> > 
> > Second, there are two points:
> > 
> > - It would be nice to check if the OF ID table doesn't provide a setting
> >   (shouldn't we try I²C ID table and then, if still nothing, bail out?)
> > 
> > - The I²C ID table can be extended in the future with another entry
> > which
> >   may want to have different default
> 
> For my understanding, please correct me if I'm wrong;
> 
> For all methods of instantiation during ht16k33 probe, i2c_of_match_device()
> matches the compatible strings in the OF ID table due to a call to
> i2c_of_match_device_sysfs().
> 
> device_get_match_data() only matches the compatible strings in the OF ID
> table for devicetree instantiation because of_match_device() won't match
> is there is no actual of_node.

That's half-true. On ACPI based platforms we may have no of_node and match
against OF ID table.

> So with only device_get_match_data() and a non devicetree instantiation,
> priv->type will always be (uintptr_t)NULL = 0 = DISP_MATRIX.

Yes.

> Which effectively breaks i.e. user-space instantiation for other display
> types which now do work due to i2c_of_match_device().
> (so my suggestion above is not sufficient).
> 
> Are you proposing extending and searching the I2C ID table to work around
> that?

See (1) above. This is the downside I have noticed after sending this series.
So, the I²C ID table match has to be restored, but the above mentioned issues
with existing table are not gone, hence they need to be addressed in the next
version.

-- 
With Best Regards,
Andy Shevchenko