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SubjectRe: [PATCH RFC 2/9] OPP: Export a number of helpers to prevent code duplication
On Thu, Mar 28, 2019 at 3:28 PM Sibi Sankar <sibis@codeaurora.org> wrote:

> +
> +/* The caller must call dev_pm_opp_put() after the OPP is used */
> +struct dev_pm_opp *dev_pm_opp_find_opp_of_np(struct opp_table *opp_table,
> + struct device_node *opp_np)
> +{
> + return _find_opp_of_np(opp_table, opp_np);
> +}
Hi Sibi,

Though this is not the latest version, we've seen following issue:

We would get lockdep warnings on this:
[ 79.068957] Call trace:
[ 79.071396] _find_opp_of_np+0xa0/0xa8
[ 79.075136] dev_pm_opp_find_opp_of_np+0x24/0x30
[ 79.079744] devfreq_passive_event_handler+0x304/0x51c
[ 79.084872] devfreq_add_device+0x368/0x434
[ 79.089046] devm_devfreq_add_device+0x68/0xb0
[ 79.093480] mtk_cci_devfreq_probe+0x108/0x158
[ 79.097915] platform_drv_probe+0x80/0xb0
[ 79.101915] really_probe+0x1b4/0x28c
[ 79.105568] driver_probe_device+0x64/0xfc
[ 79.109655] __driver_attach+0x94/0xcc
[ 79.113395] bus_for_each_dev+0x84/0xcc
[ 79.117221] driver_attach+0x2c/0x38
[ 79.120788] bus_add_driver+0x120/0x1f4
[ 79.124614] driver_register+0x64/0xf8
[ 79.128355] __platform_driver_register+0x4c/0x58
[ 79.133049] mtk_cci_devfreq_init+0x1c/0x24
[ 79.137224] do_one_initcall+0x1c0/0x3e0
[ 79.141138] do_initcall_level+0x1f4/0x224
[ 79.145225] do_basic_setup+0x34/0x4c
[ 79.148878] kernel_init_freeable+0x10c/0x194
[ 79.153225] kernel_init+0x14/0x100
[ 79.156705] ret_from_fork+0x10/0x18
[ 79.160270] irq event stamp: 238006
[ 79.163750] hardirqs last enabled at (238005):
[<ffffffa71fdea0a4>] _raw_spin_unlock_irqrestore+0x40/0x84
[ 79.173391] hardirqs last disabled at (238006):
[<ffffffa71f480e78>] do_debug_exception+0x70/0x198
[ 79.182337] softirqs last enabled at (237998):
[<ffffffa71f48165c>] __do_softirq+0x45c/0x4a4
[ 79.190850] softirqs last disabled at (237987):
[<ffffffa71f4bc0d4>] irq_exit+0xd8/0xf8
[ 79.198842] ---[ end trace 0e66a55077a0abab ]---

In _find_opp_of_np()[1], there's
lockdep_assert_held(&opp_table_lock);

[1] https://elixir.bootlin.com/linux/latest/source/drivers/opp/of.c#L75

But in governor passive.c#cpufreq_passive_register(), it call
dev_pm_opp_find_opp_of_np() directly, so it wouldn't access
opp_table_lock lock.

Another similar place is in dev_pm_opp_of_add_table(), most devfreq
would call this to get opp table.
dev_pm_opp_of_add_table
--> _opp_add_static_v2
--> _of_opp_alloc_required_opps // would goes here if opp
table contains "required-opps" property.
--> _find_opp_of_np
cpufreq-map governor needs devfreq to have "required-opps" property.
So it would also trigger above lockdep warning.


The question is: Is lockdep_assert_held(&opp_table_lock); needed in
above use cases? Since they don't need to modify device and opp lists.

Thanks

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