Re: [PATCH RFC RFT 2/3] clk: clk_put WARNs if user has not disabled clk

From: Geert Uytterhoeven
Date: Wed Sep 30 2015 - 11:38:53 EST

Hi Mike,

On Fri, Aug 7, 2015 at 9:09 PM, Michael Turquette
<mturquette@xxxxxxxxxxxx> wrote:
> From the clk_put kerneldoc in include/linux/clk.h:
> """
> Note: drivers must ensure that all clk_enable calls made on this clock
> source are balanced by clk_disable calls prior to calling this function.
> """
> The common clock framework implementation of the clk.h api has per-user
> reference counts for calls to clk_prepare and clk_disable. As such it
> can enforce the requirement to properly call clk_disable and
> clk_unprepare before calling clk_put.
> Because this requirement is probably violated in many places, this patch
> starts with a simple warning. Once offending code has been fixed this
> check could additionally release the reference counts automatically.
> Signed-off-by: Michael Turquette <mturquette@xxxxxxxxxxxx>
> ---
> drivers/clk/clk.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index 72feee9..6ec0f77 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -2764,6 +2764,14 @@ void __clk_put(struct clk *clk)
> clk->max_rate < clk->core->req_rate)
> clk_core_set_rate_nolock(clk->core, clk->core->req_rate);
> + /*
> + * before calling clk_put, all calls to clk_prepare and clk_enable from
> + * a given user must be balanced with calls to clk_disable and
> + * clk_unprepare by that same user
> + */
> + WARN_ON(clk->prepare_count);
> + WARN_ON(clk->enable_count);

These two WARN_ON()s are triggered a lot when using a legacy clock domain,
and CONFIG_PM=n. Indeed, without Runtime PM, the idea is that the module clocks
get enabled unconditionally, which violates the assumptions above.

Cfr. the CONFIG_PM=n version of pm_clk_notify() in
drivers/base/power/clock_ops.c, which calls enable_clock():

* enable_clock - Enable a device clock.
* @dev: Device whose clock is to be enabled.
* @con_id: Connection ID of the clock.
static void enable_clock(struct device *dev, const char *con_id)
struct clk *clk;

clk = clk_get(dev, con_id);
if (!IS_ERR(clk)) {
dev_info(dev, "Runtime PM disabled, clock forced on.\n");

I think this affects shmobile, keystone, davinci, omap1, and legacy sh.

Sorry for not noticing before, we usually build with CONFIG_PM=y.
One more reason for making CONFIG_PM=y mandatory on SoCs with clock domains?



Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at