[PATCH] clk: Properly update prepare/enable count on orphan clock reparent
A.s. Dong
aisheng.dong at nxp.com
Fri Jan 26 00:36:21 PST 2018
> -----Original Message-----
> From: Marek Szyprowski [mailto:m.szyprowski at samsung.com]
> Sent: Friday, January 26, 2018 3:31 PM
> To: Stephen Boyd <sboyd at codeaurora.org>
> Cc: linux-clk at vger.kernel.org; linux-arm-kernel at lists.infradead.org; Michael
> Turquette <mturquette at baylibre.com>; Shawn Guo <shawnguo at kernel.org>;
> A.s. Dong <aisheng.dong at nxp.com>; Bartlomiej Zolnierkiewicz
> <b.zolnierkie at samsung.com>
> Subject: Re: [PATCH] clk: Properly update prepare/enable count on orphan
> clock reparent
>
> Hi Stephen,
>
> On 2018-01-25 23:19, Stephen Boyd wrote:
> > On 01/15, Marek Szyprowski wrote:
> >> If orphaned clock has been already prepared/enabled (for example if
> >> it or one of its children has CLK_IS_CRITICAL flag), then the
> >> prepare/enable counters of the newly assigned parent are not updated
> >> correctly. This might later cause warnings during changing clock parents.
> >>
> >> This patch fixes following warning on Exynos5422-based boards:
> >> ------------[ cut here ]------------
> >> WARNING: CPU: 0 PID: 59 at drivers/clk/clk.c:811
> >> clk_core_disable_lock+0x18/0x24 Modules linked in:
> >> CPU: 0 PID: 59 Comm: kworker/0:1 Not tainted 4.15.0-rc7-next-20180115
> >> #106 Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
> >> Workqueue: pm genpd_power_off_work_fn [<c0111504>]
> (unwind_backtrace)
> >> from [<c010dbec>] (show_stack+0x10/0x14) [<c010dbec>] (show_stack)
> >> from [<c09b3f34>] (dump_stack+0x90/0xc8) [<c09b3f34>] (dump_stack)
> >> from [<c0125060>] (__warn+0xe4/0x110) [<c0125060>] (__warn) from
> >> [<c01250cc>] (warn_slowpath_null+0x40/0x48) [<c01250cc>]
> >> (warn_slowpath_null) from [<c048d584>]
> >> (clk_core_disable_lock+0x18/0x24) [<c048d584>]
> >> (clk_core_disable_lock) from [<c048e490>]
> >> (clk_core_disable_unprepare+0xc/0x20)
> >> [<c048e490>] (clk_core_disable_unprepare) from [<c048ea60>]
> >> (__clk_set_parent_after+0x48/0x4c)
> >> [<c048ea60>] (__clk_set_parent_after) from [<c048ec88>]
> >> (clk_core_set_parent_nolock+0x224/0x5b4)
> >> [<c048ec88>] (clk_core_set_parent_nolock) from [<c048f23c>]
> >> (clk_set_parent+0x38/0x6c) [<c048f23c>] (clk_set_parent) from
> >> [<c049c41c>] (exynos_pd_power+0x74/0x1cc) [<c049c41c>]
> >> (exynos_pd_power) from [<c0550768>] (genpd_power_off+0x164/0x264)
> >> [<c0550768>] (genpd_power_off) from [<c0550b34>]
> >> (genpd_power_off_work_fn+0x2c/0x40)
> >> [<c0550b34>] (genpd_power_off_work_fn) from [<c01432e4>]
> >> (process_one_work+0x1d0/0x7bc) [<c01432e4>] (process_one_work) from
> >> [<c014393c>] (worker_thread+0x34/0x4dc) [<c014393c>] (worker_thread)
> >> from [<c014a0d0>] (kthread+0x128/0x164) [<c014a0d0>] (kthread) from
> >> [<c01010b4>] (ret_from_fork+0x14/0x20) Exception stack(0xeeb01fb0 to
> 0xeeb01ff8)
> >> 1fa0: 00000000 00000000 00000000 00000000
> >> 1fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000
> >> 00000000
> >> 1fe0: 00000000 00000000 00000000 00000000 00000013 00000000 ---[ end
> >> trace 503c239fb760f17a ]--- ------------[ cut here ]------------
> >> WARNING: CPU: 0 PID: 59 at drivers/clk/clk.c:684
> >> clk_core_disable_unprepare+0x18/0x20
> >> Modules linked in:
> >> CPU: 0 PID: 59 Comm: kworker/0:1 Tainted: G W 4.15.0-rc7-next-
> 20180115 #106
> >> Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
> >> Workqueue: pm genpd_power_off_work_fn [<c0111504>]
> (unwind_backtrace)
> >> from [<c010dbec>] (show_stack+0x10/0x14) [<c010dbec>] (show_stack)
> >> from [<c09b3f34>] (dump_stack+0x90/0xc8) [<c09b3f34>] (dump_stack)
> >> from [<c0125060>] (__warn+0xe4/0x110) [<c0125060>] (__warn) from
> >> [<c01250cc>] (warn_slowpath_null+0x40/0x48) [<c01250cc>]
> >> (warn_slowpath_null) from [<c048e49c>]
> >> (clk_core_disable_unprepare+0x18/0x20)
> >> [<c048e49c>] (clk_core_disable_unprepare) from [<c048ea60>]
> >> (__clk_set_parent_after+0x48/0x4c)
> >> [<c048ea60>] (__clk_set_parent_after) from [<c048ec88>]
> >> (clk_core_set_parent_nolock+0x224/0x5b4)
> >> [<c048ec88>] (clk_core_set_parent_nolock) from [<c048f23c>]
> >> (clk_set_parent+0x38/0x6c) [<c048f23c>] (clk_set_parent) from
> >> [<c049c41c>] (exynos_pd_power+0x74/0x1cc) [<c049c41c>]
> >> (exynos_pd_power) from [<c0550768>] (genpd_power_off+0x164/0x264)
> >> [<c0550768>] (genpd_power_off) from [<c0550b34>]
> >> (genpd_power_off_work_fn+0x2c/0x40)
> >> [<c0550b34>] (genpd_power_off_work_fn) from [<c01432e4>]
> >> (process_one_work+0x1d0/0x7bc) [<c01432e4>] (process_one_work) from
> >> [<c014393c>] (worker_thread+0x34/0x4dc) [<c014393c>] (worker_thread)
> >> from [<c014a0d0>] (kthread+0x128/0x164) [<c014a0d0>] (kthread) from
> >> [<c01010b4>] (ret_from_fork+0x14/0x20) Exception stack(0xeeb01fb0 to
> 0xeeb01ff8)
> >> 1fa0: 00000000 00000000 00000000 00000000
> >> 1fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000
> >> 00000000
> >> 1fe0: 00000000 00000000 00000000 00000000 00000013 00000000 ---[ end
> >> trace 503c239fb760f17b ]--- ------------[ cut here ]------------
> >>
> >> Fixes: f8f8f1d04494 ("clk: Don't touch hardware when reparenting
> >> during registration")
> >> Signed-off-by: Marek Szyprowski <m.szyprowski at samsung.com>
> >> ---
> >> drivers/clk/clk.c | 4 ++++
> >> 1 file changed, 4 insertions(+)
> >>
> >> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c index
> >> 0f686a9dac3e..d33c087d7868 100644
> >> --- a/drivers/clk/clk.c
> >> +++ b/drivers/clk/clk.c
> >> @@ -2982,6 +2982,10 @@ static int __clk_core_init(struct clk_core *core)
> >> if (parent) {
> >> /* update the clk tree topology */
> >> flags = clk_enable_lock();
> > This is the spinlock?
>
> yes
>
> >
> >> + if (orphan->prepare_count)
> >> + clk_core_prepare(parent);
> > And this is prepare mutex? Doesn't sound like it will work.
>
> Prepare mutex is taken at the beginning of __clk_core_init() function, so
> everything is fine here.
>
Theoretically no issue may happen, just looks strange to claim mutex within
spinlock.
> >> + if (orphan->enable_count)
> >> + clk_core_enable(parent);
> > This would be OK, but then we might touch the hardware again?
>
> Well, it will touch hardware in one case: if orphaned clock is already prepared
> and enabled (for example due to having CLK_IS_CRITICAL flag) and the newly
> registered parent is not (yet?) enabled. Then it will prepare and enable this
> new parent clock, what is a desired behavior.
>
> This code will not temporarily disable any clocks, what I assume was the main
> reason for the patch mentioned in the commit message.
>
Then this code seems bypass the CLK_OPS_PARENT_ENABLE feature.
Regards
Dong Aisheng
> Best regards
> --
> Marek Szyprowski, PhD
> Samsung R&D Institute Poland
More information about the linux-arm-kernel
mailing list