linux-kernel - Re: [PATCH] clk: tegra: fix pllu rate configuration

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Date:   Mon, 26 Feb 2018 23:04:24 +0000
From:   Marcel Ziswiler <marcel.ziswiler@...adex.com>
To:     "digetx@...il.com" <digetx@...il.com>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jonathanh@...dia.com" <jonathanh@...dia.com>,
        "mturquette@...libre.com" <mturquette@...libre.com>,
        "pgaikwad@...dia.com" <pgaikwad@...dia.com>,
        "sboyd@...nel.org" <sboyd@...nel.org>,
        "thierry.reding@...il.com" <thierry.reding@...il.com>,
        "pdeschrijver@...dia.com" <pdeschrijver@...dia.com>,
        "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>
Subject: Re: [PATCH] clk: tegra: fix pllu rate configuration

On Mon, 2018-02-26 at 15:42 +0300, Dmitry Osipenko wrote:
> On 23.02.2018 02:04, Marcel Ziswiler wrote:
> > Turns out latest upstream U-Boot does not configure/enable pllu
> > which
> > leaves it at some default rate of 500 kHz:
> > 
> > root@...lis-t30:~# cat /sys/kernel/debug/clk/clk_summary | grep
> > pll_u
> >        pll_u                  3        3        0      500000      
> >     0
> > 
> > Of course this won't quite work leading to the following messages:
> > 
> > [    6.559593] usb 2-1: new full-speed USB device number 2 using
> > tegra-
> > ehci
> > [   11.759173] usb 2-1: device descriptor read/64, error -110
> > [   27.119453] usb 2-1: device descriptor read/64, error -110
> > [   27.389217] usb 2-1: new full-speed USB device number 3 using
> > tegra-
> > ehci
> > [   32.559454] usb 2-1: device descriptor read/64, error -110
> > [   47.929777] usb 2-1: device descriptor read/64, error -110
> > [   48.049658] usb usb2-port1: attempt power cycle
> > [   48.759475] usb 2-1: new full-speed USB device number 4 using
> > tegra-
> > ehci
> > [   59.349457] usb 2-1: device not accepting address 4, error -110
> > [   59.509449] usb 2-1: new full-speed USB device number 5 using
> > tegra-
> > ehci
> > [   70.069457] usb 2-1: device not accepting address 5, error -110
> > [   70.079721] usb usb2-port1: unable to enumerate USB device
> > 
> > Fix this by actually allowing the rate also being set from within
> > the Linux kernel.
> > 
> > Signed-off-by: Marcel Ziswiler <marcel.ziswiler@...adex.com>
> > 
> > ---
> > 
> >  drivers/clk/tegra/clk-pll.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/drivers/clk/tegra/clk-pll.c b/drivers/clk/tegra/clk-
> > pll.c
> > index 7c369e21c91c..830d1c87fa7c 100644
> > --- a/drivers/clk/tegra/clk-pll.c
> > +++ b/drivers/clk/tegra/clk-pll.c
> > @@ -1151,6 +1151,8 @@ static const struct clk_ops
> > tegra_clk_pllu_ops = {
> >  	.enable = clk_pllu_enable,
> >  	.disable = clk_pll_disable,
> >  	.recalc_rate = clk_pll_recalc_rate,
> > +	.round_rate = clk_pll_round_rate,
> > +	.set_rate = clk_pll_set_rate,
> >  };
> >  
> >  static int _pll_fixed_mdiv(struct tegra_clk_pll_params
> > *pll_params,
> > 
> 
> Tegra's USB PHY driver only enables clock and clk driver doesn't
> specify the
> clock rate in the init table. Could you please clarify where in the
> kernels code
> PLL_U rate is getting set?

I guess that would be according to the following table isn't it:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree
/drivers/clk/tegra/clk-tegra30.c?h=v4.16-rc3#n287