From: Andrew Bresticker <abrestic@google.com>
To: Thierry Reding <thierry.reding@gmail.com>
Cc: Stephen Warren <swarren@wwwdotorg.org>,
Peter De Schrijver <pdeschrijver@nvidia.com>,
Mike Turquette <mturquette@linaro.org>,
Prashant Gaikwad <pgaikwad@nvidia.com>,
Rob Herring <robh+dt@kernel.org>, Pawel Moll <pawel.moll@arm.com>,
Mark Rutland <mark.rutland@arm.com>,
Ian Campbell <ijc+devicetree@hellion.org.uk>,
Kumar Gala <galak@codeaurora.org>, Arnd Bergmann <arnd@arndb.de>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-tegra@vger.kernel.org" <linux-tegra@vger.kernel.org>,
devicetree@vger.kernel.org
Subject: Re: [RFC PATCH 3/3] clk: tegra: Implement Tegra124 shared/cbus clks
Date: Wed, 14 May 2014 10:58:26 -0700 [thread overview]
Message-ID: <CAL1qeaGS-78QaiMN-3zXYYXu+K1s7u2rFXQkt7-MRJQS1-sW5A@mail.gmail.com> (raw)
In-Reply-To: <20140514142739.GA8612@ulmo>
On Wed, May 14, 2014 at 7:27 AM, Thierry Reding
<thierry.reding@gmail.com> wrote:
> As for shared clocks I'm only aware of one use-case, namely EMC scaling.
> Using clocks for that doesn't seem like the best option to me. While it
> can probably fix the immediate issue of choosing an appropriate
> frequency for the EMC clock it isn't a complete solution for the problem
> that we're trying to solve. From what I understand EMC scaling is one
> part of ensuring quality of service. The current implementations of that
> seems to abuse clocks (essentially one X.emc clock per X clock) to
> signal the amount of memory bandwidth required by any given device. But
> there are other parts to the puzzle. Latency allowance is one. The value
> programmed to the latency allowance registers for example depends on the
> EMC frequency.
>
> Has anyone ever looked into using a different framework to model all of
> these requirements? PM QoS looks like it might fit, but if none of the
> existing frameworks have what we need, perhaps something new can be
> created.
On Exynos we use devfreq, though in that case we monitor performance
counters to determine how internal buses should be scaled - not sure
if Tegra SoCs have similar counters that could be used for this
purpose. It seems like EMC scaling would fit nicely within the PM QoS
framework, perhaps with a new PM_QOS_MEMORY_THROUGHPUT class.
-Andrew
next prev parent reply other threads:[~2014-05-14 17:58 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-13 14:06 [RFC PATCH 0/3] Introduce shared and cbus clocks Peter De Schrijver
2014-05-13 14:06 ` [RFC PATCH 1/3] clk: Implement cbus and shared clocks Peter De Schrijver
2014-05-13 14:06 ` [RFC PATCH 2/3] clk: tegra: Implement common shared clks Peter De Schrijver
2014-05-13 14:06 ` [RFC PATCH 3/3] clk: tegra: Implement Tegra124 shared/cbus clks Peter De Schrijver
2014-05-13 18:09 ` Stephen Warren
2014-05-13 21:52 ` Andrew Bresticker
2014-05-14 14:27 ` Thierry Reding
2014-05-14 17:58 ` Andrew Bresticker [this message]
2014-05-15 10:17 ` Peter De Schrijver
2014-05-14 19:35 ` Mike Turquette
2014-05-15 10:59 ` Peter De Schrijver
2014-05-26 13:07 ` Thierry Reding
2014-05-29 23:22 ` Nishanth Menon
2014-05-30 4:47 ` Mike Turquette
2014-05-30 13:24 ` Nishanth Menon
2014-05-15 10:52 ` Peter De Schrijver
2014-05-15 20:20 ` Stephen Warren
2014-05-16 19:58 ` Mike Turquette
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