Re: [PATCH] reset: thead: Scope TH1520 reset driver to VO subsystem

From: Drew Fustini <fustini@kernel.org>
To: Yao Zi <ziyao@disroot.org>
Cc: Rob Herring <robh@kernel.org>, Conor Dooley <conor+dt@kernel.org>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Alexandre Ghiti <alex@ghiti.fr>,
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-riscv@lists.infradead.org,
	Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>,
	Guo Ren <guoren@kernel.org>,
	Philipp Zabel <p.zabel@pengutronix.de>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Michal Wilczynski <m.wilczynski@samsung.com>,
	Krzysztof Kozlowski <krzk+dt@kernel.org>,
	Palmer Dabbelt <palmer@dabbelt.com>, Fu Wei <wefu@redhat.com>
Subject: Re: [PATCH] reset: thead: Scope TH1520 reset driver to VO subsystem
Date: Wed, 13 Aug 2025 11:48:41 -0700	[thread overview]
Message-ID: <aJzeCbARIRltiYE1@x1> (raw)
In-Reply-To: <aJxGnnwlE1sWarXa@pie>

On Wed, Aug 13, 2025 at 08:04:40AM +0000, Yao Zi wrote:
> On Mon, Aug 11, 2025 at 10:39:55PM -0700, Drew Fustini wrote:
> > On Sun, Aug 10, 2025 at 11:14:19PM +0200, Michal Wilczynski wrote:
> > > The reset controller driver for the TH1520 was using the generic
> > > compatible string "thead,th1520-reset". However, the current
> > > implementation only manages the resets for the Video Output (VO)
> > > subsystem.
> > 
> > Looking at Section 5.4 on Page 451 of the TH1520 System User Manual [1],
> > it does seem like we would ultimately need 6 separate nodes for reset
> > controllers:
> 
> Yes, this is true. And another six nodes for clock controllers (there's
> already one).
> 
> >  0xFF_EF01_4000: AP_SUBSYS
> >  0xFF_EC02_C000: MISC_SUBSYS
> >  0xFF_E404_0000: VI_SUBSYS
> >  0xFF_EF52_8000: VO_SUBSYS
> >  0xFF_ECC3_0000: VP_SUBSYS
> >  0xFF_EF04_0000: DSP_SUBSYS
> > 
> > Maybe we should take this opportunity to document the bindings for all
> > the resets that the REE (e.g. Linux) can control?
> 
> It's worth noting that with either mainline U-Boot or vendor U-Boot, no
> core is configured to run as REE. IOW, AON_SUBSYS could be accessed by
> AP cores as well.

Interesting, I didn't know that the AP cores could access TEE resources.
> 
> I think introducing read-only clock support to Linux could help us to
> correctly describe pvt clocks which are now replaced with a aonsys
> placeholder and resolve issues like what is described in 0370395d45ca
> ("clk: thead: Mark essential bus clocks as CLK_IGNORE_UNUSED").
> 
> Futhermore, there may be downstream projects, e.g. U-Boot, make use of
> these TEE-only devices, which could benefit if we have these devices
> documented and described in devicetree, too. Thus I think the AON clock
> and reset controllers should be documented as well if we're going to
> document every reset/clock controller in a batch.

I think that does make sense to document the AONSYS clock and reset
controllers in the DT bindings as they are part of the hardware and
described in the t-head documentation. It would be great to be able to
make use of more functionality in the t-head sdk like the ability to
reboot the board.

Thanks,
Drew

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