linux-kernel - Re: [PATCH V5 11/18] clk: tegra210: Add support for Tegra210 clocks

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Message-ID: <8bca130c-c95c-591e-2f6e-f02538f8f8b8@nvidia.com>
Date:   Thu, 18 Jul 2019 11:29:46 -0700
From:   Sowjanya Komatineni <skomatineni@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>, <sboyd@...nel.org>,
        Michael Turquette <mturquette@...libre.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>,
        <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 7/18/19 10:41 AM, Sowjanya Komatineni wrote:
>
> On 7/18/19 10:22 AM, Sowjanya Komatineni wrote:
>>
>> On 7/18/19 9:34 AM, Dmitry Osipenko wrote:
>>> 18.07.2019 4:15, Sowjanya Komatineni пишет:
>>>
>>> [snip]
>>>
>>>>>> Please try to fix all missing dependencies and orderings.
>>>>> Peter,
>>>>>
>>>>> dfllCPU_OUT is the first one to go thru restore when
>>>>> clk_restore_context traverses thru the list.
>>>>>
>>>>> dfllCPU_OUT has dependency on DFLL_ref and DFLL_SOC but this
>>>>> dependency is unknown to clock-tree.
>>>>>
>>>>> We can add DFLL_REF and DFLL_SOC as parents to dfllCPU_OUT during
>>>>> register so dfllCPU_OUT save/restore happens after their parents are
>>>>> restored.
>>>>>
>>>>> But DFLL needs both of these to be restored before DFLLCPU_Out and as
>>>>> DFLL_SOC restore always happens after the REF, thinking to add
>>>>> DFLL_SOC as parent to dfllCPU_OUT so save/restore follows after their
>>>>> dependencies.
>>>>>
>>>>> Please comment.
>>>>>
>>>> Did quick try and I see by adding dfll-soc as parent to 
>>>> dfllCPU_OUT, its
>>>> in proper order after all its dependencies.
>>>>
>>>> Can now add dfll save/restore to do dfll reinit during restore..
>>>>
>>> If dfllCPU_OUT can work properly with dfll-soc being disabled, then 
>>> this
>>> kind of dependency isn't very correct and just papers over the real
>>> problem, which is that there should be a way for CCF to specify 
>>> multiple
>>> dependencies for the clock or the reverse ordering should be used for
>>> the restoring.
>>
>> dfll will not work without dfll-soc enabled.
>>
>> CLDVFS control logic is split into 2 clock domains. dvfs_ref_clk and 
>> dvfs_soc_clk.
>>
>> Majority of the control logic is clocked from dvfs_soc_clk for 
>> interfacing control registers.
>>
> Note on reverse ordering for restore. Currently restore order goes 
> thru clock list and for each root goes thru parent -> child restore.
>
> this order is correct and also all clocks are parented properly so 
> they follow proper order.
>
> dfllCPU is the only one where current driver doesn't take care of 
> dependency in dfll_soc which gets enabled only after dfll_ref.
>
>
> Based on dfllCPU control logic module design, dfll_ref and dfll_soc 
> should be enabled prior to dfll init/enable.
>
> So parenting dfll_soc to dfllCPU keeps proper order.
>

1. With dfllCPU parenting to dfll_soc, its keeps it in expected order 
and we don't define any parent clk_ops anyway for this, so should be OK?

OR

2. Any suggestion on how to define/specify dependencies for clock other 
than parenting to follow proper order in clock tree as clk_save_context 
and clk_restore_context strictly goes thru clock tree order and all 
other clocks are parented properly except for dfllCPU where there is no 
parent. Techinically dfll_ref & dfll_soc are not parents but they need 
to be configured prior to dfll reinit.

OR

3. I don't see way to override clk_save_context/clk_restore_context APIs 
to change the way of traversal so I can modify to traverse in expected 
order without dfllCPU parenting.

OR

4. dfll re-init can be done in dfll-fcpu driver pm_ops which actually 
registers dfll or at the end of tegra210_clock resume