Re: [PATCH v1] clk: qcom: lpass: Add CLK_IGNORE_UNUSED for lpass clocks

[Taniya Das]

Hello Stephen,

On 12/21/2018 2:34 AM, Stephen Boyd wrote:
> Quoting Taniya Das (2018-12-20 03:46:25)
> > The LPASS clocks has a dependency on the GCC lpass clocks to be enabled
> > before accessing them and that was the reason to mark the gcc lpass clocks
> > as critical. But in the case where the lpass subsystem would require a
> > restart, toggling the lpass reset would from HW clear the SW enable bits
> > of the GCC lpass clocks. Thus the next time bringing up the lpass subsystem
> > out of reset would fail.
> >
> > Allow the lpass clock driver to enable/disable the gcc lpass clocks and
> > mark the lpass clocks not be accessed during late_init if no client vote.
>
> You need to add more details here. It feels like you wrote the beginning
> of a paragraph and then stopped abruptly, leaving the reader hanging for
> the whole story. Why is late_init important? Why do we need to leave
> them on from the bootloader? What if the bootloader doesn't leave them
> enabled? This is all rather hacky so I'm deeply confused. Does the lpass
> driver need to get these gcc clks and enable/prepare them during probe?
> But then it needs to also allow a reset happen and change the clk state?
>
> I suspect this situation is circling a larger problem where a reset is
> toggled and that changes some clk state without the clk framework
> knowing. There's not much we can do about that besides having some
> mechanism for the clks to know that their state is now out of sync. If
> that can be done on the provider driver side then we should have an
> easier time not needing to write a bunch of framework code to handle
> this. OMAP folks are dealing with the same problems from what I recall.

Hmm, if I mark the CLK_IS_CRITICAL, I don't see a way to handle it in 
provider. Please suggest if you think provider could handle it.

> > Signed-off-by: Taniya Das <tdas@xxxxxxxxxxxxxx>
>
> > @@ -77,6 +81,7 @@
> >                  .enable_mask = BIT(0),
> >                  .hw.init = &(struct clk_init_data){
> >                          .name = "lpass_qdsp6ss_sleep_clk",
> > +                       .flags = CLK_IGNORE_UNUSED,
>
> All uses of CLK_IGNORE_UNUSED and CLK_IS_CRITICAL need comments about
> why they're there. It's never obvious why these things are being done.

Sure, would add comments.

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