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

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Date:   Thu, 1 Mar 2018 16:44:35 +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 01.03.2018 16:19, Dmitry Osipenko wrote:
> On 01.03.2018 10:41, Peter De Schrijver wrote:
>> 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.
> 
> We can, I just don't think you can demand from Mark to do it. This patch is fine
> on its own, everything else could be done later.
I meant Marcel.