linux-kernel - Re: [PATCH] clk: ingenic-tcu: Properly enable registers before accessing timers

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Date:   Fri, 10 Jun 2022 16:43:27 +0100
From:   Aidan MacDonald <aidanmacdonald.0x0@...il.com>
To:     Stephen Boyd <sboyd@...nel.org>
Cc:     mturquette@...libre.com, paul@...pouillou.net,
        linux-mips@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clk: ingenic-tcu: Properly enable registers before
 accessing timers


Stephen Boyd <sboyd@...nel.org> writes:

> Quoting Aidan MacDonald (2022-06-03 06:47:05)
>> Access to registers is guarded by ingenic_tcu_{enable,disable}_regs()
>> so the stop bit can be cleared before accessing a timer channel, but
>> those functions did not clear the stop bit on SoCs with a global TCU
>> clock gate.
>> 
>> Testing on the X1000 has revealed that the stop bits must be cleared
>> _and_ the global TCU clock must be ungated to access timer registers.
>> Programming manuals for the X1000, JZ4740, and JZ4725B specify this
>> behavior. If the stop bit isn't cleared, then writes to registers do
>> not take effect, which can leave clocks with no defined parent when
>> registered and leave clock tree state out of sync with the hardware,
>> triggering bugs in downstream drivers relying on TCU clocks.
>> 
>> Fixing this is easy: have ingenic_tcu_{enable,disable}_regs() always
>> clear the stop bit, regardless of the presence of a global TCU gate.
>> 
>> Signed-off-by: Aidan MacDonald <aidanmacdonald.0x0@...il.com>
>> ---
>
> Any Fixes: tag?

Probably 4f89e4b8f121 ("clk: ingenic: Add driver for the TCU clocks")
but I don't have docs or hardware to confirm the bug affects the jz4770,
which is the only other SoC affected by the change.

I think what caused my problem was my bootloader stopping all the timer
channels. The stop bits are supposed to be zeroed at reset, so I'd guess
the jz4770 relied on that and only worked by accident.

I'll send a v2 along shortly. Is it worth CC'ing stable as well?