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

[Bart Van Assche]

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.