Re: [PATCH v7 4/5] clk: Provide critical clock support

[Barry Song]

2015-08-17 15:42 GMT+08:00 Lee Jones <lee.jones@xxxxxxxxxx>:
> On Mon, 17 Aug 2015, Barry Song wrote:
>
>> 2015-07-22 21:04 GMT+08:00 Lee Jones <lee.jones@xxxxxxxxxx>:
>> > Lots of platforms contain clocks which if turned off would prove fatal.
>> > The only way to recover from these catastrophic failures is to restart
>> > the board(s).  Now, when a clock provider is registered with the
>> > framework it is possible for a list of critical clocks to be supplied
>> > which must be kept ungated.  Each clock mentioned in the newly
>> > introduced 'critical-clock' property will be clk_prepare_enable()d
>> > where the normal references will be taken.  This will prevent the
>> > common clk framework from attempting to gate them during the normal
>> > clk_disable_unused() and disable_clock() procedures.
>> >
>> > Note that it will still be possible for knowledgeable drivers to turn
>> > these clocks off using clk_{enable,disable}_critical() calls.
>> >
>> > Signed-off-by: Lee Jones <lee.jones@xxxxxxxxxx>
>>
>> hi Lee,
>> i have another email about this. i am wondering whether
>> CLK_IGNORE_UNUSE is still useful after your patch. another solution
>> for your patch might be extending the current CLK_IGNORE_UNUSE to
>> runtime?
>>
>>
>> copy the mail here:
>> currently we can set a CLK_IGNORE_UNUSE flag to  a clock to stop
>> clk_disable_unused()  from disabling it at the boot stage:
>>
>> static void clk_disable_unused_subtree(struct clk_core *core)
>> {
>> ...
>>
>> if (core->flags & CLK_IGNORE_UNUSED)
>> goto unlock_out;
>> }
>>
>> static int clk_disable_unused(void)
>> {
>> ...
>>
>> clk_unprepare_unused_subtree(core);
>> ...
>>  return 0;
>> }
>>
>> late_initcall_sync(clk_disable_unused);
>>
>> so if there are two clocks A and B, A is the parent of B, and A is
>> marked as CLK_IGNORE_UNUSED.
>>
>> in boot stage if there is nobody using A and B, Linux will disable B
>> due to clk_disable_unused() , but keep A being enabled since A has
>> CLK_IGNORE_UNUSED.
>>
>> but in Linux runtime, we might frequently disable /enable B in runtime
>> power management, this will cause A disabled since Linux will not
>> check CLK_IGNORE_UNUSED for runtime disabling clk .
>>
>>  so this makes CLK_IGNORE_UNUSE only work if we don't disable its
>> sub-clock at runtime. this looks making no sense.
>>
>>  i am thinking whether we should do some changes to make it have side
>> affect for runtime clk disable. otherwise, why do we want to stop it
>> from being disabled during boot stage?
>
> This is one of this problems, along with some others that this set
> aims to solve.
>
> Extending CLK_IGNORE_UNUSED is not a good idea.  In fact, if we can
> phase it out completely, that will be a good thing.

i would agree it is better we can drop CLK_IGNORE_UNUSED since it is
confusing...


>
> Since this set Mike has submitted an alternitive solution.
>
> Please see: https://groups.google.com/forum/#!msg/linux.kernel/kX_nWSsWRxU/IZSjhG5Ed4oJ
>
>>  I am not sure whether i missed something in clk core level support.
>>
>> -barry
>>
>> > ---
>> >  drivers/clk/clk-conf.c | 45 ++++++++++++++++++++++++++++++++++++++++++++-
>> >  1 file changed, 44 insertions(+), 1 deletion(-)
>> >
>> > diff --git a/drivers/clk/clk-conf.c b/drivers/clk/clk-conf.c
>> > index aad4796..f83c1c2 100644
>> > --- a/drivers/clk/clk-conf.c
>> > +++ b/drivers/clk/clk-conf.c
>> > @@ -116,6 +116,45 @@ static int __set_clk_rates(struct device_node *node, bool clk_supplier)
>> >         return 0;
>> >  }
>> >
>> > +static int __set_critical_clocks(struct device_node *node, bool clk_supplier)
>> > +{
>> > +       struct of_phandle_args clkspec;
>> > +       struct clk *clk;
>> > +       struct property *prop;
>> > +       const __be32 *cur;
>> > +       uint32_t index;
>> > +       int ret;
>> > +
>> > +       if (!clk_supplier)
>> > +               return 0;
>> > +
>> > +       of_property_for_each_u32(node, "critical-clock", prop, cur, index) {
>> > +               clkspec.np = node;
>> > +               clkspec.args_count = 1;
>> > +               clkspec.args[0] = index;
>> > +
>> > +               clk = of_clk_get_from_provider(&clkspec);
>> > +               if (IS_ERR(clk)) {
>> > +                       pr_err("clk: couldn't get clock %u for %s\n",
>> > +                               index, node->full_name);
>> > +                       return PTR_ERR(clk);
>> > +               }
>> > +
>> > +               clk_init_critical(clk);
>> > +
>> > +               ret = clk_prepare_enable(clk);
>> > +               if (ret) {
>> > +                       pr_err("Failed to enable clock %u for %s: %d\n",
>> > +                              index, node->full_name, ret);
>> > +                       return ret;
>> > +               }
>> > +
>> > +               pr_debug("Setting clock as critical %pC\n", clk);
>> > +       }
>> > +
>> > +       return 0;
>> > +}
>> > +
>> >  /**
>> >   * of_clk_set_defaults() - parse and set assigned clocks configuration
>> >   * @node: device node to apply clock settings for
>> > @@ -139,6 +178,10 @@ int of_clk_set_defaults(struct device_node *node, bool clk_supplier)
>> >         if (rc < 0)
>> >                 return rc;
>> >
>> > -       return __set_clk_rates(node, clk_supplier);
>> > +       rc = __set_clk_rates(node, clk_supplier);
>> > +       if (rc < 0)
>> > +               return rc;
>> > +
>> > +       return __set_critical_clocks(node, clk_supplier);
>> >  }
>> >  EXPORT_SYMBOL_GPL(of_clk_set_defaults);
>
> --

-barry
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