linux-kernel - Re: [PATCH v1] clk: qcom: lpass: Add CLK_IGNORE

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Date:   Mon, 7 Jan 2019 11:56:00 +0530
From:   Taniya Das <tdas@...eaurora.org>
To:     Stephen Boyd <sboyd@...nel.org>,
        Michael Turquette <mturquette@...libre.com>
Cc:     Andy Gross <andy.gross@...aro.org>,
        David Brown <david.brown@...aro.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        linux-arm-msm@...r.kernel.org, linux-soc@...r.kernel.org,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] clk: qcom: lpass: Add CLK_IGNORE_UNUSED for lpass
 clocks

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@...eaurora.org>
> 
>> @@ -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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