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

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Message-ID: <20180301074129.GG6190@tbergstrom-lnx.Nvidia.com>
Date:   Thu, 1 Mar 2018 09:41:29 +0200
From:   Peter De Schrijver <pdeschrijver@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>
CC:     Marcel Ziswiler <marcel.ziswiler@...adex.com>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        "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>,
        "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>
Subject: Re: [PATCH] clk: tegra: fix pllu rate configuration

On Wed, Feb 28, 2018 at 08:20:47PM +0300, Dmitry Osipenko wrote:
> On 28.02.2018 17:14, Peter De Schrijver wrote:
> > On Wed, Feb 28, 2018 at 03:00:23PM +0300, Dmitry Osipenko wrote:
> >> On 28.02.2018 12:36, Peter De Schrijver wrote:
> >>> On Tue, Feb 27, 2018 at 02:59:11PM +0300, Dmitry Osipenko wrote:
> >>>> On 27.02.2018 02:04, Marcel Ziswiler wrote:
> >>>>> 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.
> >>>
> >>> I think the best solution to this problem would be to make pll_u a fixed
> >>> clock and enable it and program the rate if it's not enabled at boot.
> >>
> >> Oh, right. PLL_U rate is actually configurable, somehow I missed it in TRM
> >> yesterday.. So set/round_rate() for PLL_U are actually needed and the patch is
> >> correct. Seems only T20 misses PLL_U in the init table, probably worth to add it
> >> there.
> >>
> > 
> > AFAIK we only use one rate ever?
> 
> IIUC, PLL_U has 3 outputs and output dividers are fixed in HW. So yes, we are
> setting PLL_U to one rate - 480MHz to get out1-480MHz, out2-60MHz and out3-12MHz.
> 

Indeed. And given that it's hw controlled anyway, I don't see why we can't make
it a fixed clock and handle the init at kernel boot depending on what the
bootloader has done.

Peter.