linux-kernel - Re: [PATCH 5/6] platform/chrome: cros_ec_lpc: Correct ACPI name for Framework Laptop

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Message-ID: <Zk_63rrDJFhN1Y1q@google.com>
Date: Fri, 24 May 2024 02:26:38 +0000
From: Tzung-Bi Shih <tzungbi@...nel.org>
To: Ben Walsh <ben@...nut.com>
Cc: Benson Leung <bleung@...omium.org>, Guenter Roeck <groeck@...omium.org>,
	"Dustin L. Howett" <dustin@...ett.net>,
	Kieran Levin <ktl@...me.work>,
	Thomas Weißschuh <linux@...ssschuh.net>,
	Mario Limonciello <mario.limonciello@....com>,
	chrome-platform@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/6] platform/chrome: cros_ec_lpc: Correct ACPI name for
 Framework Laptop

On Thu, May 23, 2024 at 07:42:00PM +0100, Ben Walsh wrote:
> Tzung-Bi Shih <tzungbi@...nel.org> writes:
> 
> > On Wed, May 15, 2024 at 06:56:30AM +0100, Ben Walsh wrote:
> >> Framework Laptops' ACPI exposes the EC as name "PNP0C09". Use this to
> >> find the device. This makes it easy to find the AML mutex via the
> >> ACPI_COMPANION device.
> >>
> >> The name "PNP0C09" is part of the ACPI standard, not Chrome-specific,
> >> so only recognise the device if the DMI data is recognised too.
> >
> > I don't quite understand the statement.  Why it needs DMI data?
> 
> There are lots of computers with EC chips with ACPI name "PNP0C09"
> because it's part of the ACPI standard (for example I have an Intel NUC
> with one of these). Most of them don't support the cros_ec protocol, so
> the cros_ec driver should ignore these chips. The Framework EC is
> unusual in that it's called "PNP0C09" and supports the cros_ec protocol.
> 
> Before these patches, the cros_ec code just ignored PNP0C09 because it
> wasn't in the match table. The cros_ec_lpc_init logic looked like:
> 
>   * dmi_match => ok
>   * acpi_name == "GOOG0004" => ok
>   * otherwise fail.
> 
> After the patch, cros_ec_lpc_init still has this behaviour. We have
> "PNP0C09" in the match table so the driver gets hooked up correctly
> with the right "ACPI_COMPANION" device, but we don't allow the match
> to proceed unless we have the DMI data indicating it's a Framework EC.

>From the context you provided, instead of matching "PNP0C09" in the driver,
it makes more sense to me (for Framework EC):

* Mainly use DMI match.
* Add a quirk for looking up (acpi_get_devices()?) and binding
  (e.g. ACPI_COMPANION_SET()) the `adev` in cros_ec_lpc_probe().