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

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Message-ID: <7d8d77ca-e18d-6e37-1aca-6dd7c6e1964d@gmail.com>
Date:   Wed, 28 Feb 2018 20:20:47 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Peter De Schrijver <pdeschrijver@...dia.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 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.

>>> This is how it's done for Tegra210. The reason is that the USB IP blocks
>>> can control the pll_u state in hw. This means that if sw would disable
>>> and then re-enable the pll_u clock, but there is no USB activity, pll_u
>>> will still be disable and therefor not lock, causing an error. Today
>>> this is worked around by not polling the lock bit for pll_u, but a better
>>> solution would be to just remove all sw controls for pll_u.
>>
>> SW controls could be removed, but I don't think it is really necessary as in our
>> case SW is the PHY driver and we know what it does. Alternatively we can enable
>> PLL_U in the init table to keep it "always" enabled.