Re: [v5, PATCH 4/5] cpufreq: mediatek: add opp notification for SVS support

[andrew-sh.cheng <andrew-sh.cheng@mediatek.com>]

On Fri, 2020-03-13 at 14:40 +0530, Viresh Kumar wrote:
> On 13-03-20, 15:22, andrew-sh.cheng wrote:
> > I have something want to consult you.
> > For your previous comment, you suggest use read-write lock to replace
> > mutex lock.
> > Will it be more efficiently even when all are write lock?
> > (all lock region are "setting VProc voltage")
> 
> The data to be protected here isn't the VProc voltage but the list of
> valid OPPs. My idea was if we can make the target() routine run a bit
> faster as it really matters as it is called from scheduler hot path.
> 
> It won't be wrong to use the mutex the way you have used it right now,
> but I think the read lock is much faster, though the read/write lock
> is more beneficial in case where there are multiple readers and fewer
> writers. The target() routine gets called multiple times here, not
> in parallel, and the OPP change notifier won't be called so often.
> 
Hi Viresh,

I will use regulator in the locked region.
And regulator will use mutex_lock.

I use read_lock/write_lock, and there will be below run time error,
Is it due to read_lock/write_lock using spin lock?
write_lock() => _raw_write_lock() @ spinlock.c
Please give me some advices.
Thank you.


[   28.109082] BUG: sleeping function called from invalid context at
kernel/locking/mutex.c:254
[   28.117710] in_atomic(): 1, irqs_disabled(): 0, pid: 1855, name:
sugov:0
[   28.124788] CPU: 0 PID: 1855 Comm: sugov:0 Tainted: G        W
4.19.107 #51
[   28.132440] Hardware name: MediaTek krane sku176 board (DT)
[   28.138006] Call trace:
[   28.140461]  dump_backtrace+0x0/0x17c
[   28.144121]  show_stack+0x20/0x2c
[   28.147432]  dump_stack+0xd4/0x10c
[   28.150831]  ___might_sleep+0x108/0x118
[   28.154659]  __might_sleep+0x50/0x84
[   28.158230]  mutex_lock+0x28/0x60
[   28.161541]  regulator_lock_dependent+0x3c/0x10c
[   28.166152]  regulator_set_voltage+0x48/0xa0
[   28.170417]  mtk_cpufreq_set_voltage+0x16c/0x324
[   28.175046]  mtk_cpufreq_set_target+0x13c/0x2c8
[   28.179574]  __cpufreq_driver_target+0x424/0x4c4


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