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

[Taniya Das]

On 1/15/2019 3:55 AM, Stephen Boyd wrote:
> Quoting Taniya Das (2019-01-13 22:12:39)
> > On 1/8/2019 2:34 AM, Stephen Boyd wrote:
> > > 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?
> >
> > To enable LPASS clocks the requirement is to enable the GCC_LPASS_SWAY
> > clock.
> > 1) If the LPASS drivers are enabled/probed before the clock late init
> > the client would take care to maintain the dependency to enable the
> > GCC_LPASS_SWAY clock before enabling the LPASS clocks.
> >
> > 2) There could be a condition where the LPASS drivers would probe/init
> > later the clock late_init. When the clock_late_init would try to access
> > the LPASS clocks, since we cannot maintain the dependency this access
> > would fail. To avoid this the earlier patch has made the GCC_LPASS_SWAY
> > clock as CRITICAL.
> >
> > 3) Marking the GCC_LPASS_SWAY clock as CRITICAL has a issue, in the case
> > where the LPASS subsystem would be restarted due to some critical
> > failure on LPASS. Toggling the restart register of LPASS would clear the
> > hardware state of this clock and thus the next access of the LPASS
> > clocks would result in failure of the system.
> >
> > 4) To avoid issues happening in (2) and (3) all the LPASS clocks chould
> > be safely marked as CLK_IGNORE_UNUSED. And lpass drivers would take care
> > of the dependency to enable the required clocks.
>
> Ok, so why can't we enable/disable the lpass sway clk in the
> prepare/unprepare phase of the lpass clk driver paths? Or why can't we
> forcibly enable this lpass sway clk after the reset is deasserted? Which
> clk controller is the reset part of? GCC or LPASS?

It is part of Always On Subsystem.

> It still sounds like the LPASS clk driver isn't handling dependencies it
> has on accessing registers, but maybe we can get away with not handling
> the dependency still if we make the reset "do the right thing" and turn
> the clk back on so it stays "critical".

This is a reset from hardware and it does not bring back the clock to 
the previous state and so we can not mark it "critical". I would submit 
the next series with comments updated. Please let me know in case you 
have any comments.


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