Re: [PATCH] clk: tegra: fix pllu rate configuration

[Dmitry Osipenko <digetx@gmail.com>]

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@apalis-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.

> 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.