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

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Message-ID: <5747b78e-1956-8249-8f5e-85426b3efd01@redhat.com>
Date:   Mon, 16 Oct 2023 19:20:17 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     "Shevchenko, Andriy" <andriy.shevchenko@...el.com>,
        "Wu, Wentong" <wentong.wu@...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 18:05, Shevchenko, Andriy wrote:
> 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.

I definitely don't think we should revert the entire series since this
supports actual hw which has already been shipping for years.

But if the _ADR support is only there to support future hw and
it is not even certain yet that that future hw is actually going
to be using _ADR support then I believe that a follow-up patch
to drop _ADR support for now is in order. We can then re-introduce
it (revert the follow up patch) if future hw actually starts
using _ADR support.

Specifically what I'm suggesting is something like the following:

diff --git a/drivers/usb/misc/usb-ljca.c b/drivers/usb/misc/usb-ljca.c
index c9decd0396d4..e1bbaf964786 100644
--- a/drivers/usb/misc/usb-ljca.c
+++ b/drivers/usb/misc/usb-ljca.c
@@ -457,8 +457,8 @@ static void ljca_auxdev_acpi_bind(struct ljca_adapter *adap,
 				  u64 adr, u8 id)
 {
 	struct ljca_match_ids_walk_data wd = { 0 };
-	struct acpi_device *parent, *adev;
 	struct device *dev = adap->dev;
+	struct acpi_device *parent;
 	char uid[4];
 
 	parent = ACPI_COMPANION(dev);
@@ -466,17 +466,7 @@ static void ljca_auxdev_acpi_bind(struct ljca_adapter *adap,
 		return;
 
 	/*
-	 * get auxdev ACPI handle from the ACPI device directly
-	 * under the parent that matches _ADR.
-	 */
-	adev = acpi_find_child_device(parent, adr, false);
-	if (adev) {
-		ACPI_COMPANION_SET(&auxdev->dev, adev);
-		return;
-	}
-
-	/*
-	 * _ADR is a grey area in the ACPI specification, some
+	 * Currently LJCA hw does not use _ADR instead current
 	 * platforms use _HID to distinguish children devices.
 	 */
 	switch (adr) {

As a follow-up patch to the existing series.

Regards,

Hans