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From: Sudeep Holla <sudeep.holla@arm.com>
To: Bjorn Andersson <bjorn.andersson@linaro.org>
Cc: Viresh Kumar <viresh.kumar@linaro.org>,
	Jassi Brar <jassisinghbrar@gmail.com>,
	Arnd Bergmann <arnd@arndb.de>, Rob Herring <robh+dt@kernel.org>,
	Frank Rowand <frowand.list@gmail.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Sudeep Holla <sudeep.holla@arm.com>,
	linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [RFC] dt-bindings: mailbox: add doorbell support to ARM MHU
Date: Wed, 3 Jun 2020 19:28:05 +0100	[thread overview]
Message-ID: <20200603182805.GD23722@bogus> (raw)
In-Reply-To: <20200519012927.GT2165@builder.lan>

Hi Bjorn,

Thanks for the details response.

On Mon, May 18, 2020 at 06:29:27PM -0700, Bjorn Andersson wrote:
> On Thu 14 May 22:17 PDT 2020, Viresh Kumar wrote:
>

[...]

I find this part nicely summarise your response.

> > - With serialization, if we use only one channel as today at every
> >   priority, if there are 5 requests to send signal to the receiver and
> >   the dvfs request is the last one in queue (which may be called from
> >   scheduler's hot path with fast switching), it unnecessarily needs to
> >   wait for the first four transfers to finish due to the software
> >   locking imposed by the mailbox framework. This adds additional delay,
> >   maybe of few ms only, which isn't required by the hardware but just by
> >   the software and few ms can be important in scheduler's hotpath.
> >
>
> So these 5 requests, are they conveyed by the signals [1,2,3,4,5] or
> [BIT(0), BIT(1), BIT(2), BIT(3), BIT(4)]?
>

Latter in this case. IMO it is platform choice on how to use it. It is
equally possible to send 2^31 different signals. But the receiver must
also interpret it in the *exact* same way. In this case, the receiver
which is platform firmware interprets as individual bit signals.

> In the first case you have to serialize things given that e.g. signal 1
> immediately followed by 2 is indistinguishable from 3.
>

Agree and we are not proposing to break that use case. It exists in the
driver/binding today and will continue as is.

> If you signals are single-bit notifications then you don't need any
> serialization.
>

Indeed, we are making use of that.

--
Regards,
Sudeep

  parent reply	other threads:[~2020-06-03 18:28 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-15  5:17 [RFC] dt-bindings: mailbox: add doorbell support to ARM MHU Viresh Kumar
2020-05-15 16:46 ` Jassi Brar
2020-05-18  7:35   ` Viresh Kumar
2020-05-19  0:53     ` Jassi Brar
2020-05-19  4:39       ` Viresh Kumar
2020-05-19  1:29 ` Bjorn Andersson
2020-05-19  3:40   ` Viresh Kumar
2020-05-19  4:05     ` Jassi Brar
2020-06-03 18:31       ` Sudeep Holla
2020-06-03 18:42         ` Jassi Brar
2020-06-03 18:28   ` Sudeep Holla [this message]
2020-05-28 19:20 ` Rob Herring
2020-05-29  4:07   ` Viresh Kumar
2020-06-03 18:04     ` Sudeep Holla
2020-06-03 18:17       ` Sudeep Holla
2020-06-04  5:59         ` Viresh Kumar
2020-06-04  8:28           ` Sudeep Holla
2020-06-03 18:32       ` Jassi Brar
2020-06-04  9:20         ` Sudeep Holla
2020-06-04 15:15           ` Jassi Brar
2020-06-05  4:56             ` Sudeep Holla
2020-06-05  6:30               ` Jassi Brar
2020-06-05  8:58                 ` Sudeep Holla
2020-06-05 15:42                   ` Jassi Brar
2020-06-10  9:33                     ` Viresh Kumar
2020-06-11 10:00                       ` Sudeep Holla
2020-06-12  0:34                         ` Jassi Brar
2020-06-12  5:28                           ` Viresh Kumar
2020-09-08  9:14                             ` Arnd Bergmann
2020-09-08  9:27                               ` Viresh Kumar
2020-09-08 13:26                               ` Sudeep Holla
2020-09-09  3:23                               ` Jassi Brar
2020-09-09  4:46                                 ` Viresh Kumar
2020-09-09  9:31                                 ` Sudeep Holla
2020-05-29  5:20   ` Jassi Brar
2020-05-29  6:27     ` Viresh Kumar

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