Re: [PATCH 01/10] i2c: add suspended flag and accessors for i2c adapters

Hans de Goede
2018-12-19T18:36:54Z

Hi,

On 19-12-18 18:22, Lukas Wunner wrote:
> On Wed, Dec 19, 2018 at 05:48:17PM +0100, Wolfram Sang wrote:
>> +static inline void i2c_mark_adapter_suspended(struct i2c_adapter *adap)
>> +{
>> + i2c_lock_bus(adap, I2C_LOCK_ROOT_ADAPTER);
>> + set_bit(I2C_ALF_IS_SUSPENDED, &adap->locked_flags);
>> + i2c_unlock_bus(adap, I2C_LOCK_ROOT_ADAPTER);
>> +}
>
> This looks like a duplication of the is_suspended flag in struct dev_pm_info.
> Any reason why you can't use that? If so, it would be good to document the
> reason in the commit message.

Oh, that is a very good point and that one only gets set on system suspend
and not on resume suspend, working around the problems with the i2c-designware
driver.

I think this might be as simple as adding:

if (WARN_ON(adap->dev.parent->power.is_suspended))
return -ESHUTDOWN;

To __i2c_transfer (and document the -ESHUTDOWN) combined with removing
all the now no longer DIY code from various bus drivers.

Regards,

Hans

>
> If the point is to constrain refusal of transfers in suspended state to
> certain drivers, those drivers could opt in to that functionality by
> setting a flag, and the i2c core could then gate refusal based on
> that flag and the is_suspended flag in struct dev_pm_info.
>
> Also, why is it necessary to take a lock to perform an atomic bitop?
> (Sorry if that's a dumb question, seems non-obvious to me.)
>
> Thanks,
>
> Lukas
>