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

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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:
> > Switching to use device_get_match_data() helps getting of
> > i2c_of_match_device() API.

...

> > -	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.
>
> 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.

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

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?

Kind regards,

--
Robin van der Gracht
Protonic Holland
Factorij 36
1689AL Zwaag
+31 (0)229 212928
https://www.protonic.nl



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