Re: [PATCH V2 1/4] drivers: qcom: rpmh-rsc: simplify TCS locking

[Lina Iyer]

On Tue, Jul 23 2019 at 14:19 -0600, Stephen Boyd wrote:
> Quoting Lina Iyer (2019-07-23 12:21:59)
> > On Tue, Jul 23 2019 at 12:22 -0600, Stephen Boyd wrote:
> > >Quoting Lina Iyer (2019-07-22 14:53:37)
> > >> From: "Raju P.L.S.S.S.N" <rplsssn@xxxxxxxxxxxxxx>
> > >>
> > >> The tcs->lock was introduced to serialize access with in TCS group. But,
> > >> drv->lock is still needed to synchronize core aspects of the
> > >> communication. This puts the drv->lock in the critical and high latency
> > >> path of sending a request. drv->lock provides the all necessary
> > >> synchronization. So remove locking around TCS group and simply use the
> > >> drv->lock instead.
> > >
> > >This doesn't talk about removing the irq saving and restoring though.
> > You mean for drv->lock? It was not an _irqsave/_irqrestore anyways and
> > we were only removing the tcs->lock.
>
> Yes drv->lock wasn't an irqsave/restore variant because it was a
> spinlock inside of an obviously already irqsaved region of code because
> the tcs->lock was outside the drv->lock and that was saving the irq
> flags.
Oh, right.
> > >Can you keep irq saving and restoring in this patch and then remove that
> > >in the next patch with reasoning? It probably isn't safe if the lock is
> > >taken in interrupt context anyway.
> > >
> > Yes, the drv->lock should have been irqsave/irqrestore, but it hasn't
> > been changed by this patch.
>
> It needs to be changed to maintain the irqsaving/restoring of the code.
May be I should club this with the following patch. Instead of adding
irqsave and restore to drv->lock and then remvoing them again in the
following patch.

> > >> @@ -349,41 +349,35 @@ static int tcs_write(struct rsc_drv *drv, const struct tcs_request *msg)
> > >>  {
> > >>         struct tcs_group *tcs;
> > >>         int tcs_id;
> > >> -       unsigned long flags;
> > >>         int ret;
> > >>
> > >>         tcs = get_tcs_for_msg(drv, msg);
> > >>         if (IS_ERR(tcs))
> > >>                 return PTR_ERR(tcs);
> > >>
> > >> -       spin_lock_irqsave(&tcs->lock, flags);
> > >>         spin_lock(&drv->lock);
> > >>         /*
> > >>          * The h/w does not like if we send a request to the same address,
> > >>          * when one is already in-flight or being processed.
> > >>          */
> > >>         ret = check_for_req_inflight(drv, tcs, msg);
> > >> -       if (ret) {
> > >> -               spin_unlock(&drv->lock);
> > >> +       if (ret)
> > >>                 goto done_write;
> > >> -       }
> > >>
> > >>         tcs_id = find_free_tcs(tcs);
> > >>         if (tcs_id < 0) {
> > >>                 ret = tcs_id;
> > >> -               spin_unlock(&drv->lock);
> > >>                 goto done_write;
> > >>         }
> > >>
> > >>         tcs->req[tcs_id - tcs->offset] = msg;
> > >>         set_bit(tcs_id, drv->tcs_in_use);
> > >> -       spin_unlock(&drv->lock);
> > >>
> > >>         __tcs_buffer_write(drv, tcs_id, 0, msg);
> > >>         __tcs_trigger(drv, tcs_id);
> > >>
> > >>  done_write:
> > >> -       spin_unlock_irqrestore(&tcs->lock, flags);
> > >> +       spin_unlock(&drv->lock);
> > >>         return ret;
> > >>  }
> > >>
> > >> @@ -481,19 +475,18 @@ static int tcs_ctrl_write(struct rsc_drv *drv, const struct tcs_request *msg)
> > >>  {
> > >>         struct tcs_group *tcs;
> > >>         int tcs_id = 0, cmd_id = 0;
> > >> -       unsigned long flags;
> > >>         int ret;
> > >>
> > >>         tcs = get_tcs_for_msg(drv, msg);
> > >>         if (IS_ERR(tcs))
> > >>                 return PTR_ERR(tcs);
> > >>
> > >> -       spin_lock_irqsave(&tcs->lock, flags);
> > >> +       spin_lock(&drv->lock);
> > >>         /* find the TCS id and the command in the TCS to write to */
> > >>         ret = find_slots(tcs, msg, &tcs_id, &cmd_id);
> > >>         if (!ret)
> > >>                 __tcs_buffer_write(drv, tcs_id, cmd_id, msg);
> > >> -       spin_unlock_irqrestore(&tcs->lock, flags);
> > >> +       spin_unlock(&drv->lock);
> > >>
> > >
> > >These ones, just leave them doing the irq save restore for now?
> > >
> > drv->lock ??
>
> Yes, it should have irq save/restore still.