Re: [PATCH 1/2] clk: qcom: add API to safely park RCG2 sources

[Bjorn Andersson <bjorn.andersson@linaro.org>]

On Thu 09 Dec 00:37 PST 2021, Stephen Boyd wrote:

> Quoting Dmitry Baryshkov (2021-12-07 18:22:09)
> > Some of RCG2 clocks can become stuck during the boot process, when
> > device drivers are enabling and disabling the RCG2's parent clocks.
> > To prevernt such outcome of driver probe sequences, add API to park
> 
> s/prevernt/prevent/
> 
> > clocks to the safe clock source (typically TCXO).
> > 
> > Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
> 
> I'd prefer this approach vs. adding a new clk flag. The clk framework
> doesn't handle handoff properly today so we shouldn't try to bandage
> that in the core.
> 

I'm not against putting this responsibility in the drivers, but I don't
think we can blindly park all the RCGs that may or may not be used.

Note that we should do this for all RCGs that downstream are marked as
enable_safe_config (upstream should be using clk_rcg2_shared_ops)
and disabling some of those probe time won't be appreciated by the
hardware.


If you don't like the flag passed to clk_disable_unused (which is like a
very reasonable objection to have), we need to make progress towards a
proper solution that replaces clk_disable_unused().

> > diff --git a/drivers/clk/qcom/clk-rcg2.c b/drivers/clk/qcom/clk-rcg2.c
> > index e1b1b426fae4..230b04a7427c 100644
> > --- a/drivers/clk/qcom/clk-rcg2.c
> > +++ b/drivers/clk/qcom/clk-rcg2.c
> > @@ -1036,6 +1036,40 @@ static void clk_rcg2_shared_disable(struct clk_hw *hw)
> >         regmap_write(rcg->clkr.regmap, rcg->cmd_rcgr + CFG_REG, cfg);
> >  }
> >  
> > +int clk_rcg2_park_safely(struct regmap *regmap, u32 offset, unsigned int safe_src)

This seems to just duplicate clk_rcg2_shared_disable()?

Regards,
Bjorn

> 
> Please add kernel doc as it's an exported symbol.
> 
> > +{
> > +       unsigned int val, ret, count;
> > +
> > +       ret = regmap_read(regmap, offset + CFG_REG, &val);
> > +       if (ret)
> > +               return ret;
> > +
> > +       /* assume safe source is 0 */
> 
> Are we assuming safe source is 0 here? It looks like we pass it in now?
> 
> > +       if ((val & CFG_SRC_SEL_MASK) == (safe_src << CFG_SRC_SEL_SHIFT))
> > +               return 0;
> > +
> > +       regmap_write(regmap, offset + CFG_REG, safe_src << CFG_SRC_SEL_SHIFT);
> > +
> > +       ret = regmap_update_bits(regmap, offset + CMD_REG,
> > +                                CMD_UPDATE, CMD_UPDATE);
> > +       if (ret)
> > +               return ret;
> > +
> > +       /* Wait for update to take effect */
> > +       for (count = 500; count > 0; count--) {
> > +               ret = regmap_read(regmap, offset + CMD_REG, &val);
> > +               if (ret)
> > +                       return ret;
> > +               if (!(val & CMD_UPDATE))
> > +                       return 0;
> > +               udelay(1);
> > +       }
> > +
> > +       WARN(1, "the rcg didn't update its configuration.");
> 
> Add a newline?
> 
> > +       return -EBUSY;
> > +}
> > +EXPORT_SYMBOL_GPL(clk_rcg2_park_safely);
> > +