linux-kernel - Re: [PATCH] mailbox: add ACPI support for mailbox framework

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Date:	Tue, 7 Apr 2015 15:58:36 -0700
From:	Feng Kan <fkan@....com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	patches <patches@....com>, Jassi Brar <jassisinghbrar@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH] mailbox: add ACPI support for mailbox framework

On Tue, Apr 7, 2015 at 4:37 AM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> On Tuesday, April 07, 2015 11:41:43 AM Mika Westerberg wrote:
>> On Thu, Apr 02, 2015 at 11:04:24AM -0700, Feng Kan wrote:
>> > On Thu, Apr 2, 2015 at 2:07 AM, Mika Westerberg
>> > <mika.westerberg@...ux.intel.com> wrote:
>> > > On Wed, Apr 01, 2015 at 10:01:45AM -0700, Feng Kan wrote:
>> > >> On Wed, Apr 1, 2015 at 12:45 AM, Mika Westerberg
>> > >> <mika.westerberg@...ux.intel.com> wrote:
>> > >> > On Tue, Mar 31, 2015 at 02:18:00PM -0700, Feng Kan wrote:
>> > >> >> This will add support for ACPI parsing of the mboxes attribute
>> > >> >> when booting with ACPI table. The client will have a attribute
>> > >> >> mimic the dts call "mboxes". In the ACPI case, the client will
>> > >> >> mark "mboxes" with the ACPI HID of the mbox it wishes to use.
>> > >> >>
>> > >> >>       Name (_DSD, Package () {
>> > >> >>               ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
>> > >> >>               Package () {
>> > >> >>                       Package (2) {"mboxes", "ACPIHID"},
>> > >> >>               }
>> > >> >>       })
>> > >> >
>> > >> > Instead of this, why not match against the DT compatible property?
>> > >> >
>> > >> >         Name (_HID, "PRP0001")
>> > >> >
>> > >> >         Name (_DSD, Package () {
>> > >> >                 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
>> > >> >                 Package () {
>> > >> >                         Package (2) {"compatible", "your-dt-compatible-string"},
>> > >> >                 }
>> > >> >         })
>> > >> I think my description was not clear enough. The _DSD section is not
>> > >> meant to identify the mailbox driver, but used by the acpi node that will
>> > >> request the mailbox channel. The dts version would be as below.
>> > >>
>> > >>    mailbox: {
>> > >>    }
>> > >>
>> > >>    user-mbox: {
>> > >>       mboxes: <&mailbox 0>
>> > >>    }
>> > >>
>> > >> The mboxes attribute in the user of the mbox has to specify the HID of the
>> > >> mbox in order to retrieve channel pointer.
>> > >
>> > > Okay, then I think you can use reference instead of _HID, like
>> > >
>> > >         // The mailbox device
>> > >         Device (MLBX) {
>> > >         }
>> > >
>> > >         // User-mbox device
>> > >         Device (USBX) {
>> > >                 Name (_DSD, Package () {
>> > >                         ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
>> > >                         Package () {
>> > >                                 Package () {"mboxes", Package () {^^MLBX, 0}}),
>> > >                         }
>> > >                 })
>> > >         }
>> >
>> > Thanks, will try this. A side question on your previous reply. Would you
>> > prefer a new driver using the PRP0001 or an actual proper HID.
>>
>> If you have existing DT bindings for this, then PRP0001 is fine.
>> Otherwise you should use the proper _HID for this particular device.
>
> To be precise, PRP0001 specifically means "Use the 'compatible' property
> to find the driver for this device", so if *that* is what you want to do,
I am a bit uneasy about this. I understand the application of this. For a system
that is both DT and ACPI compatible, this would open up a flood of PRP0001
device drivers. What is the guideline here? Is this PRP0001 only exist
to support legacy devices that do not have a proper HID.

> you can use PRP0001 as the _HID.  For Windows (and such) compatibility, you
> can provide a _CID whith a (list of) proper device ID(s) in addition to that.
>
>
> --
> I speak only for myself.
> Rafael J. Wysocki, Intel Open Source Technology Center.
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