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

Barry Song
2015-08-20T13:23:25Z

2015-08-17 15:42 GMT+08:00 Lee Jones <lee.jones@linaro.org>:
> On Mon, 17 Aug 2015, Barry Song wrote:
>
>> 2015-07-22 21:04 GMT+08:00 Lee Jones <lee.jones@linaro.org>:
>> > 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@linaro.org>
>>
>> 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