linux-kernel - Re: [PATCH] clk: rockchip: rk3588: Don't change PLL rates when setting dclk_vop2

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Message-ID: <eumxn7lvp34si2gik33hcavcrsstqqoxixiznjbertxars7zcx@xsycorjhj3id>
Date: Thu, 16 Oct 2025 00:57:15 +0200
From: Sebastian Reichel <sebastian.reichel@...labora.com>
To: Heiko Stübner <heiko@...ech.de>
Cc: Quentin Schulz <quentin.schulz@...rry.de>, mturquette@...libre.com, 
	sboyd@...nel.org, zhangqing@...k-chips.com, linux-clk@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	stable@...r.kernel.org, Andy Yan <andy.yan@...k-chips.com>
Subject: Re: [PATCH] clk: rockchip: rk3588: Don't change PLL rates when
 setting dclk_vop2_src

Hi,

On Wed, Oct 15, 2025 at 03:27:12PM +0200, Heiko Stübner wrote:
> Am Mittwoch, 15. Oktober 2025, 14:58:46 Mitteleuropäische Sommerzeit schrieb Quentin Schulz:
> > Hi Heiko,
> > 
> > On 10/8/25 3:31 PM, Heiko Stuebner wrote:
> > > dclk_vop2_src currently has CLK_SET_RATE_PARENT | CLK_SET_RATE_NO_REPARENT
> > > flags set, which is vastly different than dclk_vop0_src or dclk_vop1_src,
> > > which have none of those.
> > > 
> > > With these flags in dclk_vop2_src, actually setting the clock then results
> > > in a lot of other peripherals breaking, because setting the rate results
> > > in the PLL source getting changed:
> > > 
> > > [   14.898718] clk_core_set_rate_nolock: setting rate for dclk_vop2 to 152840000
> > > [   15.155017] clk_change_rate: setting rate for pll_gpll to 1680000000
> > > [ clk adjusting every gpll user ]
> > > 
> > > This includes possibly the other vops, i2s, spdif and even the uarts.
> > > Among other possible things, this breaks the uart console on a board
> > > I use. Sometimes it recovers later on, but there will be a big block
> > 
> > I can reproduce on the same board as yours and this fixes the issue 
> > indeed (note I can only reproduce for now when display the modetest 
> > pattern, otherwise after boot the console seems fine to me).
> 
> I boot into a Debian rootfs with fbcon on my system, and the serial
> console produces garbled output when the vop adjusts the clock
> 
> Sometimes it recovers after a bit, but other times it doesn't
> 
> > Reviewed-by: Quentin Schulz <quentin.schulz@...rry.de>
> > Tested-by: Quentin Schulz <quentin.schulz@...rry.de> # RK3588 Tiger w/DP carrierboard

I'm pretty sure I've seen this while playing with USB-C DP AltMode
on Rock 5B. So far I had no time to investigate further.

What I'm missing in the commit message is the impact on VOP. Also
it might be a good idea to have Andy in Cc, so I've added him.

Greetings,

-- Sebastian

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