linux-kernel - Re: [PATCH v20 1/4] usb: Add support for Intel LJCA device

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Message-ID: <9810930b-dd76-9b1d-fb63-87a7a6059d0b@redhat.com>
Date:   Mon, 16 Oct 2023 09:35:25 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     "Wu, Wentong" <wentong.wu@...el.com>,
        "Shevchenko, Andriy" <andriy.shevchenko@...el.com>
Cc:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "oneukum@...e.com" <oneukum@...e.com>,
        "wsa@...nel.org" <wsa@...nel.org>,
        "andi.shyti@...ux.intel.com" <andi.shyti@...ux.intel.com>,
        "broonie@...nel.org" <broonie@...nel.org>,
        "bartosz.golaszewski@...aro.org" <bartosz.golaszewski@...aro.org>,
        "linus.walleij@...aro.org" <linus.walleij@...aro.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "sakari.ailus@...ux.intel.com" <sakari.ailus@...ux.intel.com>,
        "Wang, Zhifeng" <zhifeng.wang@...el.com>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v20 1/4] usb: Add support for Intel LJCA device

Hi,

On 10/16/23 07:52, Wu, Wentong wrote:
>> From: Hans de Goede <hdegoede>
>>
>> Hi Andy,
>>
>> On 10/13/23 22:05, Shevchenko, Andriy wrote:
>>> On Thu, Oct 12, 2023 at 01:14:23PM +0200, Hans de Goede wrote:
>>
>> <snip>
>>
>>>> Ah ok, I see. So the code:
>>>>
>>>> 1. First tries to find the matching child acpi_device for the auxdev
>>>> by ADR
>>>>
>>>> 2. If 1. fails then falls back to HID + UID matching
>>>>
>>>> And there are DSDTs which use either:
>>>>
>>>> 1. Only use _ADR to identify which child device is which, like the example
>>>>    DSDT snippet from the commit msg.
>>>>
>>>> 2. Only use _HID + _UID like the 2 example DSDT snippets from me
>>>> email
>>>>
>>>> But there never is a case where both _ADR and _HID are used at the
>>>> same time (which would be an ACPI spec violation as Andy said).
>>>>
>>>> So AFAICT there is no issue here since  _ADR and _HID are never user
>>>> at the same time and the commit message correctly describes scenario
>>>> 1. from above, so the commit message is fine too.
>>>>
>>>> So I believe that we can continue with this patch series in its
>>>> current v20 form, which has already been staged for going into -next
>>>> by Greg.
>>>>
>>>> Andy can you confirm that moving ahead with the current version is ok
>>>> ?
>>>
>>> Yes as we have a few weeks to fix corner cases.
>>>
>>> What I'm worrying is that opening door for _ADR that seems never used
>>> is kinda an overkill here (resolving non-existing problem).
>>
>> I assume that there actually some DSDTs using the _ADR approach and that this
>> support is not there just for fun.
> 
> right, it's not for fun, we use _ADR here is to reduce the maintain effort because
> currently it defines _HID for every new platform and the drivers have to be updated
> accordingly, while _ADR doesn't have that problem.

Hmm, this sounds to me like _ADR is currently not actually being used in any
shipping DSDTs ?

Adding support for it to the driver seems a bit premature then IMHO ?

Also HIDs can perfectly be re-used for compatible hardware in
a newer generation so that is really not a good argument to use _ADR
instead.

Regards,

Hans