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

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Message-ID: <DM6PR11MB4316711C71937AE3C0516C7B8DD7A@DM6PR11MB4316.namprd11.prod.outlook.com>
Date:   Mon, 16 Oct 2023 15:44:21 +0000
From:   "Wu, Wentong" <wentong.wu@...el.com>
To:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "Shevchenko, Andriy" <andriy.shevchenko@...el.com>
CC:     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

> 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:
> > > > > 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.
> > >
> > > 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? 

BR,
Wentong
> 
> thanks,
> 
> greg k-h