linux-kernel - Re: [PATCH v2 2/4] dt-bindings: firmware: thead,th1520: Add resets for GPU clkgen

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Message-ID: <20250416-bootlace-fossil-08a975327973@spud>
Date: Wed, 16 Apr 2025 18:10:01 +0100
From: Conor Dooley <conor@...nel.org>
To: Michal Wilczynski <m.wilczynski@...sung.com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>,
	Danilo Krummrich <dakr@...nel.org>, Pavel Machek <pavel@...nel.org>,
	Drew Fustini <drew@...7.com>, Guo Ren <guoren@...nel.org>,
	Fu Wei <wefu@...hat.com>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	Frank Binns <frank.binns@...tec.com>,
	Matt Coster <matt.coster@...tec.com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
	m.szyprowski@...sung.com, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org, linux-riscv@...ts.infradead.org,
	devicetree@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v2 2/4] dt-bindings: firmware: thead,th1520: Add resets
 for GPU clkgen

On Wed, Apr 16, 2025 at 01:40:15PM +0200, Michal Wilczynski wrote:
> 
> 
> On 4/15/25 18:38, Conor Dooley wrote:
> > On Mon, Apr 14, 2025 at 08:52:56PM +0200, Michal Wilczynski wrote:
> >> Extend the TH1520 AON firmware bindings to describe the GPU clkgen reset
> >> line, required for proper GPU clock and reset sequencing.
> >>
> >> The T-HEAD TH1520 GPU requires coordinated management of two clocks
> >> (core and sys) and two resets (GPU core reset and GPU clkgen
> >> reset).  Only the clkgen reset is exposed at the AON level, to support
> >> SoC-specific initialization handled through a generic PM domain. The GPU
> >> core reset remains described in the GPU device node, as from the GPU
> >> driver's perspective, there is only a single reset line [1].
> >>
> >> This follows upstream maintainers' recommendations [2] to abstract
> >> SoC specific details into the PM domain layer rather than exposing them
> >> to drivers directly.
> >>
> >> [1] - https://lore.kernel.org/all/816db99d-7088-4c1a-af03-b9a825ac09dc@imgtec.com/
> >> [2] - https://lore.kernel.org/all/38d9650fc11a674c8b689d6bab937acf@kernel.org/
> >>
> >> Signed-off-by: Michal Wilczynski <m.wilczynski@...sung.com>
> >> ---
> >>  .../devicetree/bindings/firmware/thead,th1520-aon.yaml        | 11 +++++++++++
> >>  1 file changed, 11 insertions(+)
> >>
> >> diff --git a/Documentation/devicetree/bindings/firmware/thead,th1520-aon.yaml b/Documentation/devicetree/bindings/firmware/thead,th1520-aon.yaml
> >> index bbc183200400de7aadbb21fea21911f6f4227b09..6ea3029c222df9ba6ea7d423b92ba248cfb02cc0 100644
> >> --- a/Documentation/devicetree/bindings/firmware/thead,th1520-aon.yaml
> >> +++ b/Documentation/devicetree/bindings/firmware/thead,th1520-aon.yaml
> >> @@ -32,6 +32,13 @@ properties:
> >>      items:
> >>        - const: aon
> >>  
> >> +  resets:
> >> +    maxItems: 1
> >> +
> >> +  reset-names:
> >> +    items:
> >> +      - const: gpu-clkgen
> >> +
> >>    "#power-domain-cells":
> >>      const: 1
> >>  
> >> @@ -39,6 +46,8 @@ required:
> >>    - compatible
> >>    - mboxes
> >>    - mbox-names
> >> +  - resets
> >> +  - reset-names
> > 
> > Given these are new required properties, have you made sure in the
> > driver that their absence will not cause problems with older
> > devicetrees? I took a brief look at the driver, and it _looked_ like you
> > were failing if they were not there? It was a brief look though, tbf.
> 
> Hi Conor,
> 
> Good point — but in this case, the devicetrees compatible with the
> driver haven’t been merged upstream yet. In fact, the TH1520 PM domains
> driver currently doesn’t even compile against mainline, since the
> required commit [1] didn’t make it into 6.15.
> 
> That said, Drew has queued the DT changes for the next release [2], and
> you’ve queued [1], so assuming this series lands in 6.16, there won’t be
> any older devicetrees to support. As a result, I haven’t added a
> fallback path in the driver for missing properties.
> 
> If, however this series doesn’t make it in for 6.16, then yes — we’d
> need to revisit the driver and add a failure safe path for cases where
> these properties aren’t present.

Can you point this reason out in the commit message please?

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