Re: [PATCH 03/13] opp: Keep track of currently programmed OPP

From: Viresh Kumar <viresh.kumar@linaro.org>
To: Ionela Voinescu <ionela.voinescu@arm.com>
Cc: Kevin Wangtao <kevin.wangtao@hisilicon.com>,
	Leo Yan <leo.yan@linaro.org>,
	Jassi Brar <jaswinder.singh@linaro.org>,
	zhongkaihua@huawei.com, Dmitry Osipenko <digetx@gmail.com>,
	Viresh Kumar <vireshk@kernel.org>, Nishanth Menon <nm@ti.com>,
	Stephen Boyd <sboyd@kernel.org>,
	linux-pm@vger.kernel.org,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Rafael Wysocki <rjw@rjwysocki.net>,
	Sibi Sankar <sibis@codeaurora.org>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 03/13] opp: Keep track of currently programmed OPP
Date: Mon, 12 Jul 2021 09:44:08 +0530	[thread overview]
Message-ID: <20210712041408.5dgtwcp55pgt7twn@vireshk-i7> (raw)
In-Reply-To: <20210709085704.GA10180@arm.com>

On 09-07-21, 09:57, Ionela Voinescu wrote:
> On Thursday 08 Jul 2021 at 13:23:53 (+0530), Viresh Kumar wrote:
> > On 07-07-21, 11:24, Ionela Voinescu wrote:
> > > Now comes the interesting part: what seems to fix it is a call to
> > > clk_get_rate(opp_table->clk) in _set_opp(), which is what basically
> > > happened before this patch, as _find_current_opp() was always called.
> > > I do not need to do anything with the returned frequency.
> > 
> > Wow, thanks for narrowing it down this far :)
> > 
> > I had a quick look and this is what I think is the problem here.
> > 
> > This platform uses mailbox API to send its frequency change requests to another
> > processor.  And the way it is written currently, I don't see any guarantee
> > whatsoever which say
> > 
> >   "once clk_set_rate() returns, the frequency would have already changed".
> > 
> 
> I think what was strange to me was that the frequency never seems to
> change, there isn't just a delay in the new frequency taking effect, as
> I would expect in these cases. Or if there is a delay, that's quite large
> - at least a second.

No idea on what the firmware is doing behind the scene :)

> > And this may exactly be the thing you are able to hit, luckily because of this
> > patchset :)
> > 
> > As a quick way of checking if that is right or not, this may make it work:
> > 
> > diff --git a/drivers/mailbox/hi3660-mailbox.c b/drivers/mailbox/hi3660-mailbox.c
> > index 395ddc250828..9856c1c84dcf 100644
> > --- a/drivers/mailbox/hi3660-mailbox.c
> > +++ b/drivers/mailbox/hi3660-mailbox.c
> > @@ -201,6 +201,9 @@ static int hi3660_mbox_send_data(struct mbox_chan *chan, void *msg)
> > 
> >         /* Trigger data transferring */
> >         writel(BIT(mchan->ack_irq), base + MBOX_SEND_REG);
> > +
> > +       hi3660_mbox_check_state(chan);
> > +
> 
> I gave this a try an it does work for me.

Good, so that kind of proves what I was suspecting. The mailbox driver looks
buggy here.

> > -------------------------8<-------------------------
> > 
> > As a proper fix, something like this (not even compile tested) is required I
> > believe as I don't see the clients would know if the transfer is over. Cc'ing
> > mailbox guys to see what can be done.
> > 
> 
> I'll give this a try as well when there is consensus. I might even try to
> review it, if the time allows.

Sure, lets see what the platform guys think about this first.

Kevin, Kaihua ?

-- 
viresh