linux-kernel - Re: [RFC PATCH 3/3] clk: tegra: Implement Tegra124 shared/cbus clks

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 14 May 2014 10:58:26 -0700
From:	Andrew Bresticker <abrestic@...gle.com>
To:	Thierry Reding <thierry.reding@...il.com>
Cc:	Stephen Warren <swarren@...dotorg.org>,
	Peter De Schrijver <pdeschrijver@...dia.com>,
	Mike Turquette <mturquette@...aro.org>,
	Prashant Gaikwad <pgaikwad@...dia.com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Arnd Bergmann <arnd@...db.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	devicetree@...r.kernel.org
Subject: Re: [RFC PATCH 3/3] clk: tegra: Implement Tegra124 shared/cbus clks

On Wed, May 14, 2014 at 7:27 AM, Thierry Reding
<thierry.reding@...il.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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/