Re: [PATCH] mfd: max77620: Avoid regmap mutex deadlock in power-off handler

[Dmitry Osipenko <digetx@gmail.com>]

20.05.2026 19:23, Mark Brown пишет:
> On Wed, May 20, 2026 at 05:19:00PM +0100, Lee Jones wrote:
>> On Wed, 20 May 2026, Diogo Ivo wrote:
> 
>>> This patch was motivated by the Sashiko review I got in [1]. Its point
>>> here is that there is a possibility for a deadlock scenario in which
>>> a secondary CPU obtains the mutex for the regmap and then smp_send_stop()
>>> is called before this secondary CPU gets a chance to release the mutex,
>>> making it so that when the primary CPU tries to acquire it to issue the
>>> write it hangs. Is there something that I am misunderstanding here?
>>>
> 
>> It's my understanding that using the Regmap wrappers _prevents_ locking
>> issues, rather than causes them.
> 
> In the case where the CPU is being powered off during a regmap write
> there is a potential issue - as Diogo says if we're in the middle of
> holding the lock and we power off the CPU that owns the lock then it
> will never be able to release the lock.  I would expect the same issue
> to apply to a bus like I2C or SPI though, they'll hold a lock while
> they're in the middle of doing bus I/O unless you use some special API.

Sounds bad

Diogo, check if shutdown works with added nosmp to kernel's cmdline.

BTW, you can use i2c_smbus_read_byte_data+i2c_smbus_write_byte_data to
keep the old regmap_update_bits behaviour.