Re: [PATCH v6] clk: qcom: Add lpass clock controller driver for SDM845

[Taniya Das]

On 10/17/2018 5:07 PM, Taniya Das wrote:
> Hello Stephen,
>
> On 10/12/2018 11:05 PM, Stephen Boyd wrote:
> > Quoting Taniya Das (2018-10-09 23:12:27)
> > > On 10/10/2018 2:22 AM, Stephen Boyd wrote:
> > > > Quoting Taniya Das (2018-10-09 10:26:38)
> > > > > Hello Stephen,
> > > > >
> > > > > On 10/8/2018 8:14 AM, Stephen Boyd wrote:
> > > > > > Quoting Taniya Das (2018-10-04 05:02:26)
> > > > > > > Add support for the lpass clock controller found on SDM845 based 
> > > > > > > devices.
> > > > > > > This would allow lpass peripheral loader drivers to control the 
> > > > > > > clocks to
> > > > > > > bring the subsystem out of reset.
> > > > > > > LPASS clocks present on the global clock controller would be 
> > > > > > > registered
> > > > > > > with the clock framework based on the device tree flag. Also do 
> > > > > > > not gate
> > > > > > > these clocks if they are left unused.
> > > > > >
> > > > > > Why not gate them? This statement states what the code is doing, 
> > > > > > not why
> > > > > > it's doing it which is the more crucial information that should be
> > > > > > described in the commit text. Also, please add a comment about it 
> > > > > > to the
> > > > > > code next to the flag.
> > > > > >
> > > > > > I am concerned that it doesn't make any sense though, so probably it
> > > > > > shouldn't be marked as CLK_IGNORE_UNUSED and it's papering over some
> > > > > > other larger bug that needs to be fixed.
> > > > >
> > > > > It does not have any bug, it is just that to access these lpass
> > > > > registers we would need the GCC lpass registers to be enabled. I would
> > > > > update the same in the commit text.
> > > > >
> > > > > During clock late_init these clocks should not be accessed to check 
> > > > > the
> > > > > clock status as they would result in unclocked access. The client 
> > > > > would
> > > > > request these clocks in the correct order and it would not have any 
> > > > > issue.
> > > >
> > > > That seems like the bug right there. If the LPASS registers can't be
> > > > accessed unless the clks in GCC are enabled then this driver needs to
> > > > turn the clks on before reading/writing registers. Marking the clks as
> > > > ignore unused is skipping around the real problem.
> > >
> > > If the driver requests for the clocks they would maintain the order. But
> > > if the clock late init call is invoked before the driver requests, there
> > > is no way I could manage this dependency, that is the only reason to
> > > mark them unused.
> >
> > Which driver are we talking about here? The lpass clk driver? Presumably
> > the lpass clk driver would request the GCC clks and turn them on in
> > probe and then register any lpass clks. If the lpass clk driver probes
> > bfeore late init, then the gcc clks will be enabled and everything
> > works, and if the lpass clk driver probes after late init then the clks
> > that can't be touched without gcc clks enabled won't be registered, and
> > then they won't be touched. What goes wrong?
>
> Okay, sure, I will take the GCC clock handles and then enable/disable 
> them accordingly.
>
> I missed earlier, so here is what you suggest

gcc_probe --> GCC LPASS clocks registered.
lpass_probe --> clk_get on gcc_lpass_clocks/ clk_prepare_enable -->
register the lpass clocks --> clk_disable_unprepare gcc_lpass_clocks.

But the problem is not during the above. It is the below
static void clk_disable_unused_subtree(struct clk_core *core)
{
....

        if (clk_core_is_enabled(core)) {  --> This access fails.
....

}

Please let me know your comments in case I missed something.
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