Message-ID: <093462f3-8c6d-d084-9822-ae4eff041c64@nvidia.com>
Date:   Tue, 16 Jul 2019 22:55:52 -0700
From:   Sowjanya Komatineni <skomatineni@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>
CC:     Peter De Schrijver <pdeschrijver@...dia.com>,
        Joseph Lo <josephl@...dia.com>, <thierry.reding@...il.com>,
        <jonathanh@...dia.com>, <tglx@...utronix.de>,
        <jason@...edaemon.net>, <marc.zyngier@....com>,
        <linus.walleij@...aro.org>, <stefan@...er.ch>,
        <mark.rutland@....com>, <pgaikwad@...dia.com>, <sboyd@...nel.org>,
        <linux-clk@...r.kernel.org>, <linux-gpio@...r.kernel.org>,
        <jckuo@...dia.com>, <talho@...dia.com>,
        <linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <mperttunen@...dia.com>, <spatra@...dia.com>, <robh+dt@...nel.org>,
        <devicetree@...r.kernel.org>
Subject: Re: [PATCH V5 11/18] clk: tegra210: Add support for Tegra210 clocks


On 7/16/19 10:42 PM, Dmitry Osipenko wrote:
> В Tue, 16 Jul 2019 22:25:25 -0700
> Sowjanya Komatineni <skomatineni@...dia.com> пишет:
>
>> On 7/16/19 9:11 PM, Dmitry Osipenko wrote:
>>> В Tue, 16 Jul 2019 19:35:49 -0700
>>> Sowjanya Komatineni <skomatineni@...dia.com> пишет:
>>>   
>>>> On 7/16/19 7:18 PM, Sowjanya Komatineni wrote:
>>>>> On 7/16/19 3:06 PM, Sowjanya Komatineni wrote:
>>>>>> On 7/16/19 3:00 PM, Dmitry Osipenko wrote:
>>>>>>> 17.07.2019 0:35, Sowjanya Komatineni пишет:
>>>>>>>> On 7/16/19 2:21 PM, Dmitry Osipenko wrote:
>>>>>>>>> 17.07.2019 0:12, Sowjanya Komatineni пишет:
>>>>>>>>>> On 7/16/19 1:47 PM, Dmitry Osipenko wrote:
>>>>>>>>>>> 16.07.2019 22:26, Sowjanya Komatineni пишет:
>>>>>>>>>>>> On 7/16/19 11:43 AM, Dmitry Osipenko wrote:
>>>>>>>>>>>>> 16.07.2019 21:30, Sowjanya Komatineni пишет:
>>>>>>>>>>>>>> On 7/16/19 11:25 AM, Dmitry Osipenko wrote:
>>>>>>>>>>>>>>> 16.07.2019 21:19, Sowjanya Komatineni пишет:
>>>>>>>>>>>>>>>> On 7/16/19 9:50 AM, Sowjanya Komatineni wrote:
>>>>>>>>>>>>>>>>> On 7/16/19 8:00 AM, Dmitry Osipenko wrote:
>>>>>>>>>>>>>>>>>> 16.07.2019 11:06, Peter De Schrijver пишет:
>>>>>>>>>>>>>>>>>>> On Tue, Jul 16, 2019 at 03:24:26PM +0800, Joseph Lo
>>>>>>>>>>>>>>>>>>> wrote:
>>>>>>>>>>>>>>>>>>>>> OK, Will add to CPUFreq driver...
>>>>>>>>>>>>>>>>>>>>>> The other thing that also need attention is that
>>>>>>>>>>>>>>>>>>>>>> T124 CPUFreq
>>>>>>>>>>>>>>>>>>>>>> driver
>>>>>>>>>>>>>>>>>>>>>> implicitly relies on DFLL driver to be probed
>>>>>>>>>>>>>>>>>>>>>> first, which is
>>>>>>>>>>>>>>>>>>>>>> icky.
>>>>>>>>>>>>>>>>>>>>>>      
>>>>>>>>>>>>>>>>>>>>> Should I add check for successful dfll clk
>>>>>>>>>>>>>>>>>>>>> register explicitly in
>>>>>>>>>>>>>>>>>>>>> CPUFreq driver probe and defer till dfll clk
>>>>>>>>>>>>>>>>>>>>> registers?
>>>>>>>>>>>>>>>>>> Probably you should use the "device links". See
>>>>>>>>>>>>>>>>>> [1][2] for the
>>>>>>>>>>>>>>>>>> example.
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> [1]
>>>>>>>>>>>>>>>>>> https://elixir.bootlin.com/linux/v5.2.1/source/drivers/gpu/drm/tegra/dc.c#L2383
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> [2]
>>>>>>>>>>>>>>>>>> https://www.kernel.org/doc/html/latest/driver-api/device_link.html
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> Return EPROBE_DEFER instead of EINVAL if
>>>>>>>>>>>>>>>>>> device_link_add() fails.
>>>>>>>>>>>>>>>>>> And
>>>>>>>>>>>>>>>>>> use of_find_device_by_node() to get the DFLL's
>>>>>>>>>>>>>>>>>> device, see [3].
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> [3]
>>>>>>>>>>>>>>>>>> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/devfreq/tegra20-devfreq.c#n100
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>      
>>>>>>>>>>>>>>>>> Will go thru and add...
>>>>>>>>>>>>>>> Looks like I initially confused this case with getting
>>>>>>>>>>>>>>> orphaned clock.
>>>>>>>>>>>>>>> I'm now seeing that the DFLL driver registers the clock
>>>>>>>>>>>>>>> and then
>>>>>>>>>>>>>>> clk_get(dfll) should be returning EPROBE_DEFER until
>>>>>>>>>>>>>>> DFLL driver is
>>>>>>>>>>>>>>> probed, hence everything should be fine as-is and there
>>>>>>>>>>>>>>> is no real
>>>>>>>>>>>>>>> need
>>>>>>>>>>>>>>> for the 'device link'. Sorry for the confusion!
>>>>>>>>>>>>>>>      
>>>>>>>>>>>>>>>>>>>> Sorry, I didn't follow the mail thread. Just
>>>>>>>>>>>>>>>>>>>> regarding the DFLL
>>>>>>>>>>>>>>>>>>>> part.
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> As you know it, the DFLL clock is one of the CPU
>>>>>>>>>>>>>>>>>>>> clock sources and
>>>>>>>>>>>>>>>>>>>> integrated with DVFS control logic with the
>>>>>>>>>>>>>>>>>>>> regulator. We will not
>>>>>>>>>>>>>>>>>>>> switch
>>>>>>>>>>>>>>>>>>>> CPU to other clock sources once we switched to
>>>>>>>>>>>>>>>>>>>> DFLL. Because the
>>>>>>>>>>>>>>>>>>>> CPU has
>>>>>>>>>>>>>>>>>>>> been regulated by the DFLL HW with the DVFS table
>>>>>>>>>>>>>>>>>>>> (CVB or OPP
>>>>>>>>>>>>>>>>>>>> table
>>>>>>>>>>>>>>>>>>>> you see
>>>>>>>>>>>>>>>>>>>> in the driver.). We shouldn't reparent it to other
>>>>>>>>>>>>>>>>>>>> sources with
>>>>>>>>>>>>>>>>>>>> unknew
>>>>>>>>>>>>>>>>>>>> freq/volt pair. That's not guaranteed to work. We
>>>>>>>>>>>>>>>>>>>> allow switching to
>>>>>>>>>>>>>>>>>>>> open-loop mode but different sources.
>>>>>>>>>>>>>>>>>> Okay, then the CPUFreq driver will have to enforce
>>>>>>>>>>>>>>>>>> DFLL freq to
>>>>>>>>>>>>>>>>>> PLLP's
>>>>>>>>>>>>>>>>>> rate before switching to PLLP in order to have a
>>>>>>>>>>>>>>>>>> proper CPU voltage.
>>>>>>>>>>>>>>>>> PLLP freq is safe to work for any CPU voltage. So no
>>>>>>>>>>>>>>>>> need to enforce
>>>>>>>>>>>>>>>>> DFLL freq to PLLP rate before changing CCLK_G source
>>>>>>>>>>>>>>>>> to PLLP during
>>>>>>>>>>>>>>>>> suspend
>>>>>>>>>>>>>>>>>      
>>>>>>>>>>>>>>>> Sorry, please ignore my above comment. During suspend,
>>>>>>>>>>>>>>>> need to change
>>>>>>>>>>>>>>>> CCLK_G source to PLLP when dfll is in closed loop mode
>>>>>>>>>>>>>>>> first and
>>>>>>>>>>>>>>>> then
>>>>>>>>>>>>>>>> dfll need to be set to open loop.
>>>>>>>>>>>>>>> Okay.
>>>>>>>>>>>>>>>      
>>>>>>>>>>>>>>>>>>>> And I don't exactly understand why we need to
>>>>>>>>>>>>>>>>>>>> switch to PLLP in
>>>>>>>>>>>>>>>>>>>> CPU
>>>>>>>>>>>>>>>>>>>> idle
>>>>>>>>>>>>>>>>>>>> driver. Just keep it on CL-DVFS mode all the time.
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> In SC7 entry, the dfll suspend function moves it
>>>>>>>>>>>>>>>>>>>> the open-loop
>>>>>>>>>>>>>>>>>>>> mode. That's
>>>>>>>>>>>>>>>>>>>> all. The sc7-entryfirmware will handle the rest of
>>>>>>>>>>>>>>>>>>>> the sequence to
>>>>>>>>>>>>>>>>>>>> turn off
>>>>>>>>>>>>>>>>>>>> the CPU power.
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> In SC7 resume, the warmboot code will handle the
>>>>>>>>>>>>>>>>>>>> sequence to
>>>>>>>>>>>>>>>>>>>> turn on
>>>>>>>>>>>>>>>>>>>> regulator and power up the CPU cluster. And leave
>>>>>>>>>>>>>>>>>>>> it on PLL_P.
>>>>>>>>>>>>>>>>>>>> After
>>>>>>>>>>>>>>>>>>>> resuming to the kernel, we re-init DFLL, restore
>>>>>>>>>>>>>>>>>>>> the CPU clock
>>>>>>>>>>>>>>>>>>>> policy (CPU
>>>>>>>>>>>>>>>>>>>> runs on DFLL open-loop mode) and then moving to
>>>>>>>>>>>>>>>>>>>> close-loop mode.
>>>>>>>>>>>>>>>>>> The DFLL is re-inited after switching CCLK to DFLL
>>>>>>>>>>>>>>>>>> parent during of
>>>>>>>>>>>>>>>>>> the
>>>>>>>>>>>>>>>>>> early clocks-state restoring by CaR driver. Hence
>>>>>>>>>>>>>>>>>> instead of having
>>>>>>>>>>>>>>>>>> odd
>>>>>>>>>>>>>>>>>> hacks in the CaR driver, it is much nicer to have a
>>>>>>>>>>>>>>>>>> proper suspend-resume sequencing of the device
>>>>>>>>>>>>>>>>>> drivers. In this case
>>>>>>>>>>>>>>>>>> CPUFreq
>>>>>>>>>>>>>>>>>> driver is the driver that enables DFLL and switches
>>>>>>>>>>>>>>>>>> CPU to that
>>>>>>>>>>>>>>>>>> clock
>>>>>>>>>>>>>>>>>> source, which means that this driver is also should
>>>>>>>>>>>>>>>>>> be responsible for
>>>>>>>>>>>>>>>>>> management of the DFLL's state during of
>>>>>>>>>>>>>>>>>> suspend/resume process. If
>>>>>>>>>>>>>>>>>> CPUFreq driver disables DFLL during suspend and
>>>>>>>>>>>>>>>>>> re-enables it
>>>>>>>>>>>>>>>>>> during
>>>>>>>>>>>>>>>>>> resume, then looks like the CaR driver hacks around
>>>>>>>>>>>>>>>>>> DFLL are not
>>>>>>>>>>>>>>>>>> needed.
>>>>>>>>>>>>>>>>>>      
>>>>>>>>>>>>>>>>>>>> The DFLL part looks good to me. BTW, change the
>>>>>>>>>>>>>>>>>>>> patch subject to
>>>>>>>>>>>>>>>>>>>> "Add
>>>>>>>>>>>>>>>>>>>> suspend-resume support" seems more appropriate to
>>>>>>>>>>>>>>>>>>>> me.
>>>>>>>>>>>>>>>>>>> To clarify this, the sequences for DFLL use are as
>>>>>>>>>>>>>>>>>>> follows (assuming
>>>>>>>>>>>>>>>>>>> all
>>>>>>>>>>>>>>>>>>> required DFLL hw configuration has been done)
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> Switch to DFLL:
>>>>>>>>>>>>>>>>>>> 0) Save current parent and frequency
>>>>>>>>>>>>>>>>>>> 1) Program DFLL to open loop mode
>>>>>>>>>>>>>>>>>>> 2) Enable DFLL
>>>>>>>>>>>>>>>>>>> 3) Change cclk_g parent to DFLL
>>>>>>>>>>>>>>>>>>> For OVR regulator:
>>>>>>>>>>>>>>>>>>> 4) Change PWM output pin from tristate to output
>>>>>>>>>>>>>>>>>>> 5) Enable DFLL PWM output
>>>>>>>>>>>>>>>>>>> For I2C regulator:
>>>>>>>>>>>>>>>>>>> 4) Enable DFLL I2C output
>>>>>>>>>>>>>>>>>>> 6) Program DFLL to closed loop mode
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> Switch away from DFLL:
>>>>>>>>>>>>>>>>>>> 0) Change cclk_g parent to PLLP so the CPU frequency
>>>>>>>>>>>>>>>>>>> is ok for
>>>>>>>>>>>>>>>>>>> any
>>>>>>>>>>>>>>>>>>> vdd_cpu voltage
>>>>>>>>>>>>>>>>>>> 1) Program DFLL to open loop mode
>>>>>>>>>>>>>>>>>>>      
>>>>>>>>>>>>>>>> I see during switch away from DFLL (suspend), cclk_g
>>>>>>>>>>>>>>>> parent is not
>>>>>>>>>>>>>>>> changed to PLLP before changing dfll to open loop mode.
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> Will add this ...
>>>>>>>>>>>>>>> The CPUFreq driver switches parent to PLLP during the
>>>>>>>>>>>>>>> probe, similar
>>>>>>>>>>>>>>> should be done on suspend.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> I'm also wondering if it's always safe to switch to PLLP
>>>>>>>>>>>>>>> in the probe.
>>>>>>>>>>>>>>> If CPU is running on a lower freq than PLLP, then some
>>>>>>>>>>>>>>> other more
>>>>>>>>>>>>>>> appropriate intermediate parent should be selected.
>>>>>>>>>>>>>>>      
>>>>>>>>>>>>>> CPU parents are PLL_X, PLL_P, and dfll. PLL_X always runs
>>>>>>>>>>>>>> at higher
>>>>>>>>>>>>>> rate
>>>>>>>>>>>>>> so switching to PLL_P during CPUFreq probe prior to dfll
>>>>>>>>>>>>>> clock enable
>>>>>>>>>>>>>> should be safe.
>>>>>>>>>>>>> AFAIK, PLLX could run at ~200MHz. There is also a divided
>>>>>>>>>>>>> output of
>>>>>>>>>>>>> PLLP
>>>>>>>>>>>>> which CCLKG supports, the PLLP_OUT4.
>>>>>>>>>>>>>
>>>>>>>>>>>>> Probably, realistically, CPU is always running off a fast
>>>>>>>>>>>>> PLLX during
>>>>>>>>>>>>> boot, but I'm wondering what may happen on KEXEC. I guess
>>>>>>>>>>>>> ideally CPUFreq driver should also have a 'shutdown'
>>>>>>>>>>>>> callback to teardown DFLL
>>>>>>>>>>>>> on a reboot, but likely that there are other clock-related
>>>>>>>>>>>>> problems as
>>>>>>>>>>>>> well that may break KEXEC and thus it is not very
>>>>>>>>>>>>> important at the
>>>>>>>>>>>>> moment.
>>>>>>>>>>>>>
>>>>>>>>>>>>> [snip]
>>>>>>>>>>>> During bootup CPUG sources from PLL_X. By PLL_P source
>>>>>>>>>>>> above I meant
>>>>>>>>>>>> PLL_P_OUT4.
>>>>>>>>>>>>
>>>>>>>>>>>> As per clock policies, PLL_X is always used for high freq
>>>>>>>>>>>> like
>>>>>>>>>>>>> 800Mhz
>>>>>>>>>>>> and for low frequency it will be sourced from PLLP.
>>>>>>>>>>> Alright, then please don't forget to pre-initialize
>>>>>>>>>>> PLLP_OUT4 rate to a
>>>>>>>>>>> reasonable value using tegra_clk_init_table or
>>>>>>>>>>> assigned-clocks.
>>>>>>>>>> PLLP_OUT4 rate update is not needed as it is safe to run at
>>>>>>>>>> 408Mhz because it is below fmax @ Vmin
>>>>>>>>> So even 204MHz CVB entries are having the same voltage as
>>>>>>>>> 408MHz, correct? It's not instantly obvious to me from the
>>>>>>>>> DFLL driver's code where the fmax @ Vmin is defined, I see
>>>>>>>>> that there is the min_millivolts
>>>>>>>>> and frequency entries starting from 204MHZ defined
>>>>>>>>> per-table.
>>>>>>>> Yes at Vmin CPU Fmax is ~800Mhz. So anything below that will
>>>>>>>> work at Vmin voltage and PLLP max is 408Mhz.
>>>>>>> Thank you for the clarification. It would be good to have that
>>>>>>> commented
>>>>>>> in the code as well.
>>>>>> OK, Will add...
>>>>> Regarding, adding suspend/resume to CPUFreq, CPUFreq suspend
>>>>> happens very early even before disabling non-boot CPUs and also
>>>>> need to export clock driver APIs to CPUFreq.
>>>>>
>>>>> Was thinking of below way of implementing this...
>>>>>
>>>>>
>>>>> Clock DFLL driver Suspend:
>>>>>
>>>>>           - Save CPU clock policy registers, and Perform dfll
>>>>> suspend which sets in open loop mode
>>>>>
>>>>> CPU Freq driver Suspend: does nothing
>>>>>
>>>>>
>>>>> Clock DFLL driver Resume:
>>>>>
>>>>>           - Re-init DFLL, Set in Open-Loop mode, restore CPU Clock
>>>>> policy registers which actually sets source to DFLL along with
>>>>> other CPU Policy register restore.
>>>>>
>>>>> CPU Freq driver Resume:
>>>>>
>>>>>           - do clk_prepare_enable which acutally sets DFLL in
>>>>> Closed loop mode
>>>>>
>>>>>
>>>>> Adding one more note: Switching CPU Clock to PLLP is not needed as
>>>>> CPU CLock can be from dfll in open-loop mode as DFLL is not
>>>>> disabled anywhere throught the suspend/resume path and SC7 entry
>>>>> FW and Warm boot code will switch CPU source to PLLP.
>>> Since CPU resumes on PLLP, it will be cleaner to suspend it on PLLP
>>> as well. And besides, seems that currently disabling DFLL clock will
>>> disable DFLL completely and then you'd want to re-init the DFLL on
>>> resume any ways. So better to just disable DFLL completely on
>>> suspend, which should happen on clk_disable(dfll).
>> Will switch to PLLP during CPUFreq suspend. With decision of using
>> clk_disable during suspend, its mandatory to switch to PLLP as DFLL
>> is completely disabled.
>>
>> My earlier concern was on restoring CPU policy as we can't do that
>> from CPUFreq driver and need export from clock driver.
>>
>> Clear now and will do CPU clock policy restore in after dfll re-init.
> Why the policy can't be saved/restored by the CaR driver as a context of
> any other clock?

restoring cpu clock policy involves programming source and 
super_cclkg_divider.

cclk_g is registered as clk_super_mux and it doesn't use frac_div ops to 
do save/restore its divider.

Also, during clock context we cant restore cclk_g as cclk_g source will 
be dfll and dfll will not be resumed/re-initialized by the time 
clk_super_mux save/restore happens.

we can't use save/restore context for dfll clk_ops because dfllCPU_out 
parent to CCLK_G is first in the clock tree and dfll_ref and dfll_soc 
peripheral clocks are not restored by the time dfll restore happens. 
Also dfll peripheral clock enables need to be restored before dfll 
restore happens which involves programming dfll controller for 
re-initialization.

So dfll resume/re-init is done in clk-tegra210 at end of all clocks 
restore in V5 series but instead of in clk-tegra210 driver I moved now 
to dfll-fcpu driver pm_ops as all dfll dependencies will be restored 
thru clk_restore_context by then. This will be in V6.

>> Also I don't see Tegra124 CPU Freq driver using flag
>> CPUFREQ_NEED_INITIAL_FREQ_CHECK.
>>
>> Tegra124 CPUFreq driver is not using cpufreq_driver
>>
>>
>> <https://elixir.bootlin.com/linux/v5.2.1/ident/cpufreq_driver>
>>
> T124 driver is a wrapper around cpufreq-dt driver.

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