linux-kernel - Re: [PATCH v1 2/3] auxdisplay: ht16k33: Make use of device_get_match

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Message-ID: <06f29d66-f16a-039c-ecd0-155bdcce00c1@linaro.org>
Date:   Wed, 22 Feb 2023 19:46:25 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Robin van der Gracht <robin@...tonic.nl>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>
Cc:     "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 22/02/2023 18:20, Andy Shevchenko wrote:
>>
>>> 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

Does anything actually rely on i2c_device_id table? ACPI would match
either via ACPI or OF tables. All modern ARM systems (e.g. imx6) are
DT-based. Maybe just drop the I2C ID table?

> - the OF ID table seems has something really badly formed for adafruit
>   (just a number after a comma)

Maybe it is a model number? It was documented:
Documentation/devicetree/bindings/auxdisplay/holtek,ht16k33.yaml

> 
> 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?
> 

Best regards,
Krzysztof