linux-kernel - Re: [PATCH v5 1/3] dt-bindings: mailbox: add google,gs101-mbox

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Message-ID: <CABb+yY0AkpqC_P-3cHeuWDu-gJzxCnarsNFNQWk45+tHKrDLmg@mail.gmail.com>
Date: Thu, 2 Jan 2025 21:39:04 -0600
From: Jassi Brar <jassisinghbrar@...il.com>
To: Tudor Ambarus <tudor.ambarus@...aro.org>
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
	Conor Dooley <conor+dt@...nel.org>, Krzysztof Kozlowski <krzk@...nel.org>, 
	Alim Akhtar <alim.akhtar@...sung.com>, linux-kernel@...r.kernel.org, 
	linux-samsung-soc@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, andre.draszik@...aro.org, 
	peter.griffin@...aro.org, kernel-team@...roid.com, willmcvicker@...gle.com, 
	daniel.lezcano@...aro.org, vincent.guittot@...aro.org, ulf.hansson@...aro.org, 
	arnd@...db.de
Subject: Re: [PATCH v5 1/3] dt-bindings: mailbox: add google,gs101-mbox

On Sat, Dec 21, 2024 at 12:45 AM Tudor Ambarus <tudor.ambarus@...aro.org> wrote:
>
> Hi, Jassi,
>
> Thanks for the review!
>
> On 12/21/24 2:19 AM, Jassi Brar wrote:
> > On Thu, Dec 19, 2024 at 4:51 AM Tudor Ambarus <tudor.ambarus@...aro.org> wrote:
> >>
> >> Hi, Krzysztof, Jassi,
> >>
> >> On 12/17/24 9:40 AM, Tudor Ambarus wrote:
> >>
> >>> diff --git a/Documentation/devicetree/bindings/mailbox/google,gs101-mbox.yaml b/Documentation/devicetree/bindings/mailbox/google,gs101-mbox.yaml
> >>
> >> cut
> >>
> >>> +
> >>> +  '#mbox-cells':
> >>> +    description: |
> >>> +      <&phandle type channel>
> >>> +      phandle : label name of controller.
> >>> +      type    : channel type, doorbell or data-transfer.
> >>> +      channel : channel number.
> >>> +
> >>> +      Here is how a client can reference them:
> >>> +      mboxes = <&ap2apm_mailbox DOORBELL 2>;
> >>> +      mboxes = <&ap2apm_mailbox DATA 3>;
> >>> +    const: 2
> >>> +
> >>
> >> Revisiting this, I think that for the ACPM interface mailbox client use
> >> case, it would be better to introduce a mbox property where I reference
> >> just the phandle to the controller:
> >>         mbox = <&ap2apm_mailbox>;
> >>
> >> The ACPM interface discovers the mailbox channel IDs at runtime by
> >> parsing SRAM. And all ACPM's channels are of type DOORBELL, thus
> >> specifying the type and channel in DT is redundant.
> >>
> >> It would require to extend a bit the mailbox core to provide a
> >> mbox_request_channel_by_args() method. I already wrote a draft and
> >> tested it.
> >>
> >> Do you find the idea fine?
> >>
> > Looking at v6, I prefer this version... maybe modify it a bit.
>
> Just to summarize for the readers, in the end I chose for the
> controllers to allow #mbox-cells = <0>; and for the clients to still use
> the mboxes property, but just to reference the phandle to the controller:
>         mboxes = <&ap2apm_mailbox>;
>
This was already supported, see drivers/mailbox/bcm2835-mailbox.c for example.

> Then I updated the mailbox core to allow clients to request channels by
> passing some args containing channel identifiers to the controllers,
> that the controllers xlate() using their own method.
>
This is unnecessary.
If you don't pass the doorbell number from DT, each channel populated
by the driver is just a s/w construct or a 'virtual' channel. Make use
of 'void *data'  in send_data() to specify the doorbell.

Cheers.
Jassi