Re: [PATCH v6 3/3] clk: qcom: Add Global Clock controller (GCC) driver for SDM845

[Amit Nischal]

On 2018-05-05 08:44, Stephen Boyd wrote:
> Quoting Amit Nischal (2018-05-04 03:45:12)
> > On 2018-05-02 12:53, Stephen Boyd wrote:
> > > Quoting Amit Nischal (2018-04-30 09:20:10)
> > >> +
> > >> +static struct clk_branch gcc_disp_gpll0_clk_src = {
> > >> +       .halt_reg = 0x52004,
> > >> +       .halt_check = BRANCH_HALT_DELAY,
> > >
> > > What about this one? It's not a phy so I'm confused again why we're
> > > unable to check the halt bit. To be clear(er), I don't see why we ever
> > > want to have HALT_DELAY used. Hopefully we can remove that flag.
> > >
> > > From what I recall, the flag is there for clks that don't toggle their
> > > status bit at all, but that we know take a few cycles to ungate the
> > > upstream clk. So we threw a delay into the code to make sure that when
> > > clk_enable() returned, a driver wouldn't try to use hardware before the
> > > clk was actually on. But these cases should pretty much never happen,
> > > hence all the pushback against this flag.
> > >
> >
> > For these "*gpll0_clk_src" and "*gpll0_div_clk" clocks, there is no 
> > halt
> > bit to check the status and it is required to have delay for few 
> > cycles
> > so that clock gets turned on before a client driver to use the 
> > hardware.
>
> Ok.. but then why is there a 'halt_reg' configured for the clk?

Thanks for the review.
I will remove the halt_reg for the clocks where we are using the 
'HALT_DELAY'
flag and there is no need to poll the status bit as we are returning 
early
from the 'clk_branch_wait()' function.

> > >> +
> > >> +static struct clk_branch gcc_ufs_card_rx_symbol_0_clk = {
> > >> +       .halt_reg = 0x75018,
> > >> +       .halt_check = BRANCH_HALT_DELAY,
> > >
> > > There are still HALT_DELAY flags for UFS though? Why?
> >
> > For ufs_card tx/rx symbol clocks, we don't poll the status bit as
> > per the recommendation from the HW team. We can change the halt_check
> > type to newly implemented flag "BRANCH_HALT_SKIP". Please update us 
> > with
> > your thoughts to change the flag to "BRANCH_HALT_SKIP".
>
> Yes use HALT_SKIP please.

Thanks for confirming. I will do the changes in the next patch series.

> > >
> > > Also, are you going to send DFS support for the QUP clks? I would like
> > > to see that code merged soon.
> >
> > Taniya has sent the patches for DFS support for QUP clocks.
> > https://patchwork.kernel.org/patch/10376951/
>
> I'll take a look.
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