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

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Date:   Thu, 18 Jul 2019 12:11:03 -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 11:29 AM, Sowjanya Komatineni wrote:
>
> 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.

instead of using core API of save/restore context, probably can change 
traversing to skip the 1st root in clock tree during initial traversing 
and at the end invoke restore for 1st node.

>
> 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
>
Please suggest if you agree with either 1/3/4.