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Message-ID: <153092068418.143105.5823916627333449732@swboyd.mtv.corp.google.com>
Date: Fri, 06 Jul 2018 16:44:44 -0700
From: Stephen Boyd <sboyd@...nel.org>
To: Gregory CLEMENT <gregory.clement@...tlin.com>,
Mike Turquette <mturquette@...libre.com>,
Stephen Boyd <sboyd@...eaurora.org>
Cc: linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
Andrew Lunn <andrew@...n.ch>,
Jason Cooper <jason@...edaemon.net>,
Hua Jing <jinghua@...vell.com>,
Antoine Tenart <antoine.tenart@...tlin.com>,
stable@...r.kernel.org,
Maxime Chevallier <maxime.chevallier@...tlin.com>,
Nadav Haklai <nadavh@...vell.com>, Ken Ma <make@...vell.com>,
Victor Gu <xigu@...vell.com>,
Neta Zur Hershkovits <neta@...vell.com>,
Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
Miquèl Raynal <miquel.raynal@...tlin.com>,
Marcin Wojtas <mw@...ihalf.com>,
Wilson Ding <dingwei@...vell.com>,
linux-arm-kernel@...ts.infradead.org,
Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Subject: Re: [PATCH 1/2] clk: mvebu: armada-37xx-periph: Fix switching CPU rate from
300Mhz to 1.2GHz
Quoting Gregory CLEMENT (2018-06-29 07:44:02)
> Hi,
>
> On mar., juin 19 2018, Gregory CLEMENT <gregory.clement@...tlin.com> wrote:
>
> > Switching the CPU from the L2 or L3 frequencies (300 and 200 Mhz
> > respectively) to L0 frequency (1.2 Ghz) requires a significant amount
> > of time to let VDD stabilize to the appropriate voltage. This amount of
> > time is large enough that it cannot be covered by the hardware
> > countdown register. Due to this, the CPU might start operating at L0
> > before the voltage is stabilized, leading to CPU stalls.
> >
> > To work around this problem, we prevent switching directly from the
> > L2/L3 frequencies to the L0 frequency, and instead switch to the L1
> > frequency in-between. The sequence therefore becomes:
> >
> > 1. First switch from L2/L3(200/300MHz) to L1(600MHZ)
> > 2. Sleep 20ms for stabling VDD voltage
> > 3. Then switch from L1(600MHZ) to L0(1200Mhz).
>
> Do you have any comment on this fix?
>
Looks good. Is it crashing right now? I can throw it into clk-fixes if
it's fixing pain.
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