Date:   Thu, 23 Feb 2023 09:19:57 +0100
From:   Robin van der Gracht <robin@...tonic.nl>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>,
        Raul E Rangel <rrangel@...omium.org>,
        Wolfram Sang <wsa@...nel.org>, linux-kernel@...r.kernel.org,
        linux-i2c@...r.kernel.org, linux-usb@...r.kernel.org,
        Miguel Ojeda <ojeda@...nel.org>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v1 2/3] auxdisplay: ht16k33: Make use of
 device_get_match_data()

On 2023-02-22 18:20, Andy Shevchenko wrote:
> + Cc: OF bindings people for the mess with the IDs.
> 
> On Wed, Feb 22, 2023 at 07:01:40PM +0200, Andy Shevchenko wrote:
>> 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.
> 
> I see now what you mean. So, we have even more issues in this driver:
> - I²C table is not in sync with all devices supported
> - the OF ID table seems has something really badly formed for adafruit
>   (just a number after a comma)
> 
> The latter shows how broken it is. The I²C ID table mechanism is used 
> as
> a backward compatibility to the OF. Unfortunately, user space may not 
> provide
> the data except in form of DT overlays, so for the legacy enumeration 
> we
> have only device name, which is a set of 4 digits for adafruit case.
> 
> Now imagine if by some reason we will get adafruit2 (you name it) with
> the same schema. How I²C framework can understand that you meant 
> adafruit
> and not adafruit2? Or did I miss something?

I agree.

I've added Geert Uytterhoeven to the CC. He added support for the 
adafruit
segment displays. Maybe he has a comment on this.

Kind regards,
Robin van der Gracht

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