Re: [PATCH v4 2/3] scsi: ufs: core: Introduce a new clock_gating lock

[Bart Van Assche <bvanassche@acm.org>]

On 11/21/24 1:06 PM, Avri Altman wrote:
>> On 11/18/24 6:41 AM, Avri Altman wrote:
>>> +     spin_lock_irqsave(hba->host->host_lock, flags);
>>> +     if (ufshcd_has_pending_tasks(hba) ||
>>> +         hba->ufshcd_state != UFSHCD_STATE_OPERATIONAL) {
>>> +             spin_unlock_irqrestore(hba->host->host_lock, flags);
>>> +             return;
>>> +     }
>>> +     spin_unlock_irqrestore(hba->host->host_lock, flags);
>>
>> Why explicit lock/unlock calls instead of using scoped_guard()?
> Should I apply those to host_lock as well?

Yes, please use scoped_guard() and guard() in new code. I expect that
using scoped_guard() here will lead to code that is easier to read.

>>> + * @clk_gating_workq: workqueue for clock gating work.
>>> + * @lock: serialize access to some struct ufs_clk_gating members
>>
>> Please document that @lock is the outer lock relative to the host lock.
> Not sure what you mean?
> host_lock is nested in one place only, should this goes to the @lock documentation?

Whenever locks are nested, the nesting order must be consistent
everywhere. Otherwise there is a risk of triggering an ABBA deadlock.
So I think it is a good practice to document in which order locks should
be nested.

Thanks,

Bart.