linux-kernel - Re: [PATCH 03/21] dt-bindings: gpu: img: Power domain details

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Message-ID: <20241106-embassy-busload-2093b80d012a@spud>
Date: Wed, 6 Nov 2024 18:28:51 +0000
From: Conor Dooley <conor@...nel.org>
To: Matt Coster <Matt.Coster@...tec.com>
Cc: Frank Binns <Frank.Binns@...tec.com>, David Airlie <airlied@...il.com>,
	Simona Vetter <simona@...ll.ch>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, Nishanth Menon <nm@...com>,
	Vignesh Raghavendra <vigneshr@...com>,
	Tero Kristo <kristo@...nel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
	Randolph Sapp <rs@...com>, Darren Etheridge <detheridge@...com>
Subject: Re: [PATCH 03/21] dt-bindings: gpu: img: Power domain details

On Wed, Nov 06, 2024 at 10:18:01AM +0000, Matt Coster wrote:
> On 05/11/2024 18:13, Conor Dooley wrote:
> > On Tue, Nov 05, 2024 at 06:05:54PM +0000, Conor Dooley wrote:
> >> On Tue, Nov 05, 2024 at 03:58:09PM +0000, Matt Coster wrote:
> >>> The single existing GPU (AXE-1-16M) only requires a single power domain.
> >>> Subsequent patches will add support for BXS-4-64 MC1, which has two power
> >>> domains. Add infrastructure now to allow for this.
> >>>
> >>> Signed-off-by: Matt Coster <matt.coster@...tec.com>
> >>> ---
> >>>  .../devicetree/bindings/gpu/img,powervr-rogue.yaml | 29 +++++++++++++++++++++-
> >>>  1 file changed, 28 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/Documentation/devicetree/bindings/gpu/img,powervr-rogue.yaml b/Documentation/devicetree/bindings/gpu/img,powervr-rogue.yaml
> >>> index 6924831d3e9dd9b2b052ca8f9d7228ff25526532..55f422be1bc5b7564e3e81f24c4b93857f3e12fe 100644
> >>> --- a/Documentation/devicetree/bindings/gpu/img,powervr-rogue.yaml
> >>> +++ b/Documentation/devicetree/bindings/gpu/img,powervr-rogue.yaml
> >>> @@ -49,7 +49,16 @@ properties:
> >>>      maxItems: 1
> >>>  
> >>>    power-domains:
> >>> -    maxItems: 1
> >>> +    minItems: 1
> >>> +    maxItems: 2
> >>> +
> >>> +  power-domain-names:
> >>> +    oneOf:
> >>> +      - items:
> >>> +          - const: a
> >>> +      - items:
> >>> +          - const: a
> >>> +          - const: b
> > 
> > Additionally, a & b? Are those actually the names for the power domains?
> 
> Sadly yes, Rogue has power domains that are literally just A, B, etc. I
> wouldn't believe me either; the attached image is taken directly from
> the documentation for BXS-4-64.

heh, nice... Also - if you have the oneOf stuff here for the same reason
as the locks, the same logic with min/maxItems applies here.

> 
> >>>  
> >>>  required:
> >>>    - compatible
> >>> @@ -57,10 +66,27 @@ required:
> >>>    - clocks
> >>>    - clock-names
> >>>    - interrupts
> >>> +  - power-domains
> >>> +  - power-domain-names
> >>
> >> A new required property is an ABI break. Please explain why this is
> >> acceptable in your commit message.
> 
> Strictly it's only necessary for multi-domain GPUs, or perhaps in
> instances where the SoC power controller already enforces the
> dependencies between power domains. In reality, I think it was simply an
> oversight not to enfore this requirement in the first place. We have
> very, very few cores that require <2 power domains so names are always
> required if domains are enumerated in dt.
> 
> Would you prefer we drop the requirement for "power-domains" and gate
> the requirement for "power-domain-names" behind >2 domains, or just
> explain the change properly and make the ABI break now while only one
> core is supported?

I dunno, depends really on whether or not it is possible to have power
domain "a" and domain "c" in a rogue gpu. If "a" and "b" is all it will
ever be, the order is fixed by the binding and you can do
genpd_dev_pm_attach_by_id() instead of genpd_dev_pm_attach_by_name().

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