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

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Message-ID: <154689507747.15366.6553307032295093169@swboyd.mtv.corp.google.com>
Date:   Mon, 07 Jan 2019 13:04:37 -0800
From:   Stephen Boyd <sboyd@...nel.org>
To:     Michael Turquette <mturquette@...libre.com>,
        Taniya Das <tdas@...eaurora.org>
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

Quoting Taniya Das (2019-01-06 22:26:00)
> 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.

As far as I know, I'm not suggesting the use of CLK_IS_CRITICAL here.
But removing CLK_IS_CRITICAL and relying on some random bootloader
behavior also looks wrong. Can you clarify what's going on?