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From: Stephen Boyd <swboyd@chromium.org>
To: Lina Iyer <ilina@codeaurora.org>
Cc: agross@kernel.org, bjorn.andersson@linaro.org,
	linux-arm-msm@vger.kernel.org, linux-soc@vger.kernel.org,
	rnayak@codeaurora.org, linux-kernel@vger.kernel.org,
	linux-pm@vger.kernel.org, dianders@chromium.org,
	mkshah@codeaurora.org,
	"Raju P.L.S.S.S.N" <rplsssn@codeaurora.org>
Subject: Re: [PATCH V2 1/4] drivers: qcom: rpmh-rsc: simplify TCS locking
Date: Tue, 23 Jul 2019 13:18:58 -0700
Message-ID: <5d376bb3.1c69fb81.2bb4e.7771@mx.google.com> (raw)
In-Reply-To: <20190723192159.GA18620@codeaurora.org>

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@codeaurora.org>
> >>
> >> 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.

> 
> >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.

> >> @@ -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.


  reply index

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-22 21:53 Lina Iyer
2019-07-22 21:53 ` [PATCH V2 2/4] drivers: qcom: rpmh-rsc: avoid locking in the interrupt handler Lina Iyer
2019-07-23 20:11   ` Stephen Boyd
2019-07-24 14:52     ` Lina Iyer
2019-07-24 19:37       ` Stephen Boyd
2019-07-24 20:36         ` Lina Iyer
2019-07-24 23:27           ` Doug Anderson
2019-07-25 15:18             ` Lina Iyer
2019-07-25 15:39               ` Doug Anderson
2019-07-29 19:01                 ` Lina Iyer
2019-07-29 20:56                   ` Stephen Boyd
2019-07-30 17:29                     ` Lina Iyer
2019-07-22 21:53 ` [PATCH V2 3/4] drivers: qcom: rpmh: switch over from spinlock irq variants Lina Iyer
2019-07-23 18:24   ` Stephen Boyd
2019-07-22 21:53 ` [PATCH V2 4/4] drivers: qcom: rpmh-rsc: remove redundant register access Lina Iyer
2019-07-23 18:22 ` [PATCH V2 1/4] drivers: qcom: rpmh-rsc: simplify TCS locking Stephen Boyd
2019-07-23 19:21   ` Lina Iyer
2019-07-23 20:18     ` Stephen Boyd [this message]
2019-07-24 14:54       ` Lina Iyer
2019-07-24 18:32         ` Stephen Boyd
2019-07-24 19:36           ` Lina Iyer

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