linux-kernel - Re: [PATCH v2 1/3] clk: thead: add support for enabling/disabling PLLs

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Message-ID: <aJ59AfgQNHUpMM7x@x1>
Date: Thu, 14 Aug 2025 17:19:13 -0700
From: Drew Fustini <fustini@...nel.org>
To: Icenowy Zheng <uwu@...nowy.me>
Cc: Guo Ren <guoren@...nel.org>, Fu Wei <wefu@...hat.com>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...nel.org>,
	Michal Wilczynski <m.wilczynski@...sung.com>,
	Yao Zi <ziyao@...root.org>, Han Gao <rabenda.cn@...il.com>,
	linux-riscv@...ts.infradead.org, linux-clk@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] clk: thead: add support for enabling/disabling
 PLLs

On Wed, Aug 13, 2025 at 03:27:00PM +0800, Icenowy Zheng wrote:
> The 2nd control word of T-Head TH1520 PLLs contains a bit to put the VCO
> into reset state, which means disabling the PLL.
> 
> Some PLLs are put to disabled state by the bootloader, and the clock
> driver should be able to enable them.
> 
> Add support for enabling/disabling PLLs. PLLs other than DPU ones are
> set CLK_IS_CRITICAL to prevent killing the system -- they're meant to
> drive CPU or system buses (even the GMAC/Video ones are driving arbitrary
> buses).

Do you think there is a way in the future to allow disabling PLLs for
run-time power management?  I think it is more important right now to
get hardware peripherals working upstream like you are doing, but I was
curious if there is the potential to do something more granular in the
future.

> Signed-off-by: Icenowy Zheng <uwu@...nowy.me>
> ---
> No changes in v2.
> 
>  drivers/clk/thead/clk-th1520-ap.c | 38 +++++++++++++++++++++++++++----
>  1 file changed, 33 insertions(+), 5 deletions(-)

Reviewed-by: Drew Fustini <fustini@...nel.org>