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

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Message-ID: <ZS1fSPhfREVlELLD@smile.fi.intel.com>
Date:   Mon, 16 Oct 2023 19:05:28 +0300
From:   "Shevchenko, Andriy" <andriy.shevchenko@...el.com>
To:     "Wu, Wentong" <wentong.wu@...el.com>
Cc:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        Hans de Goede <hdegoede@...hat.com>,
        "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

On Mon, Oct 16, 2023 at 06:44:21PM +0300, Wu, Wentong wrote:
> > From: gregkh@...uxfoundation.org
> > On Mon, Oct 16, 2023 at 03:05:09PM +0000, Wu, Wentong wrote:
> > > > From: Shevchenko, Andriy
> > > > On Mon, Oct 16, 2023 at 08:52:28AM +0300, Wu, Wentong wrote:

...

> > > > But this does not confirm if you have such devices. Moreover, My
> > > > question about _CID per function stays the same. Why firmware is not using
> > it?
> > >
> > > Yes, both _ADR and _CID can stop growing list in the driver. And for
> > > _ADR, it also only require one ID per function. I don't know why BIOS
> > > team doesn't select _CID, but I have suggested use _ADR internally,
> > > and , to make things moving forward, the driver adds support for _ADR here
> > first.
> > >
> > > But you're right, _CID is another solution as well, we will discuss it
> > > with firmware team more.
> > 
> > Should I revert this series now until this gets sorted out?
> 
> Current _ADR support is a solution, I don't think _CID is better than _ADR to both
> stop growing list in driver and support the shipped hardware at the same time.
> 
> Andy, what's your idea? 

In my opinion if _CID can be made, it's better than _ADR. As using _ADR like
you do is a bit of grey area in the ACPI specification. I.o.w. can you get
a confirmation, let's say, from Microsoft, that they will go your way for other
similar devices?

Btw, Microsoft has their own solution actually using _ADR for the so called
"wired" USB devices. Is it your case? If so, I'm not sure why _HID has been
used from day 1...

Also I suggest to wait for Hans' opinion on the topic.

-- 
With Best Regards,
Andy Shevchenko