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

From: Sowjanya Komatineni
Date: Thu Jul 18 2019 - 14:29:51 EST



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 ÐÐÑÐÑ:

[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