linux-kernel - Re: [PATCH] clk: tegra: rework pll

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Message-ID: <20170320143705.GJ21907@tbergstrom-lnx.Nvidia.com>
Date:   Mon, 20 Mar 2017 16:37:05 +0200
From:   Peter De Schrijver <pdeschrijver@...dia.com>
To:     Thierry Reding <thierry.reding@...il.com>
CC:     Prashant Gaikwad <pgaikwad@...dia.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        "Stephen Warren" <swarren@...dotorg.org>,
        Alexandre Courbot <gnurou@...il.com>,
        <linux-clk@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] clk: tegra: rework pll_u

On Mon, Mar 20, 2017 at 02:20:21PM +0100, Thierry Reding wrote:
> * PGP Signed by an unknown key
> 
> On Tue, Mar 14, 2017 at 04:12:49PM +0200, Peter De Schrijver wrote:
> > In normal operation pll_u is under hardware control and has a fixed rate of
> > 480MHz. Hardware will turn on pll_u on whenever any of the XUSB
> > powerdomains is on. From a software point of view we model this is if pll_u
> > is always on using a fixed rate clock. However the bootloader might or
> > might not have configured pll_u this way. So we will check the current
> > state of pll_u at boot and reconfigure it if required.
> > 
> > There are 3 possiblities at kernel boot:
> > 1) pll_u is under hardware control: do nothing
> > 2) pll_u is under hardware control and enabled: enable hardware control
> > 3) pll_u is disabled: enable pll_u and enable hardware control
> > 
> > In all cases we also check if UTMIPLL is under hardware control at boot
> > and configure it for hardware control if that is not the case.
> > The same is done during SC7 resume.
> > 
> > Thanks to Joseph Lo <josephl@...dia.com> for bug fixes.
> > 
> > Signed-off-by: Peter De Schrijver <pdeschrijver@...dia.com>
> > ---
> >  drivers/clk/tegra/clk-pll.c      | 174 -----------------------
> >  drivers/clk/tegra/clk-tegra210.c | 295 ++++++++++++++++++++++++++++++++++++---
> >  2 files changed, 272 insertions(+), 197 deletions(-)
> 
> Applied, thanks.
> 
> Do you think this actually fixes a bug? We've had a long standing issue
> with booting Debian on a Jetson TX1 which is due to some USB related PLL
> failing to lock. This sounds like it could fix that particular issue.
> 

I think the current approach does have problems if the PLL is already under
hw control.

Cheers,

Peter.