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From: Viresh Kumar <>
To: Nicolas Saenz Julienne <>
Subject: Re: [RFC v2 0/5] cpufreq support for the Raspberry Pi
Date: Mon, 20 May 2019 16:21:53 +0530
Message-ID: <20190520105153.ftlnjx7ocr2qkxhd@vireshk-i7> (raw)
In-Reply-To: <>

On 20-05-19, 12:47, Nicolas Saenz Julienne wrote:
> Hi all,
> as some of you may recall I've been spending some time looking into
> providing 'cpufreq' support for the Raspberry Pi platform[1]. I think
> I'm close to something workable, so I'd love for you to comment on it.
> There has been some design changes since the last version. Namely the
> fact that I now make sure *only* the CPU frequency is updated. The
> firmware API we use has two modes, with or without turbo. Enabling turbo
> implies not only scaling the CPU clock but also the VPU and other
> peripheral related clocks.  This is problematic as some of them are not
> prepared for this kind frequency changes. I spent some time adapting the
> peripheral drivers, but the result was disappointing as they poorly
> support live frequency changes (which most other chips accept, think for
> instance I2C and clock stretching) but also turned out hard to integrate
> into the kernel. As we were planning to use 'clk_notifiers' which turns
> out not to be such a good idea as it's prone to deadlocks and not
> recommended by the clock maintainers[2]. It's also worth mentioning that
> the foundation kernel doesn't support VPU frequency scaling either.
> With this in mind, and as suggested by clock maintainers[2], I've
> decided to integrate the firmware clock interface into the bcm2835 clock
> driver. This, in my opinion, provides the least friction with the
> firmware and lets us write very simple and portable higher level
> drivers. As I did with the 'cpufreq' driver which simply queries the max
> and min frequencies available, which are configurable in the firmware,
> to then trigger the generic 'cpufreq-dt'.
> In the future we could further integrate other firmware dependent clocks
> into the main driver. For instance to be able to scale the VPU clock,
> which should be operated through a 'devfreq' driver.
> This was tested on a RPi3b+ and if the series is well received I'll test
> it further on all platforms I own.

Please always supply version history on what has changed from V1. And
why do you keep sending it as RFC ? Just keep the default PATCH thing,
the patches are in good shape I would say.


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Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-20 10:47 Nicolas Saenz Julienne
2019-05-20 10:47 ` [RFC v2 1/5] clk: bcm2835: set CLK_GET_RATE_NOCACHE on CPU clocks Nicolas Saenz Julienne
2019-05-20 11:42   ` Stefan Wahren
2019-05-20 10:47 ` [RFC v2 2/5] clk: bcm2835: set pllb_arm divisor as readonly Nicolas Saenz Julienne
2019-05-20 11:43   ` Stefan Wahren
2019-05-20 10:47 ` [RFC v2 3/5] clk: bcm2835: use firmware interface to update pllb Nicolas Saenz Julienne
2019-05-20 12:11   ` Stefan Wahren
2019-05-20 12:14     ` Stefan Wahren
2019-05-21 12:40     ` Stefan Wahren
2019-05-21 15:47       ` Nicolas Saenz Julienne
2019-05-21 21:43         ` Stefan Wahren
2019-05-23  8:51           ` Nicolas Saenz Julienne
2019-05-20 12:43   ` Oliver Neukum
2019-05-21 11:39     ` Nicolas Saenz Julienne
2019-05-21 12:14       ` Petr Tesarik
2019-05-21 12:18         ` Nicolas Saenz Julienne
2019-05-20 10:47 ` [RFC v2 4/5] dts: bcm2837: add per-cpu clock devices Nicolas Saenz Julienne
2019-05-20 12:19   ` Stefan Wahren
2019-05-21 11:40     ` Nicolas Saenz Julienne
2019-05-20 10:47 ` [RFC v2 5/5] cpufreq: add driver for Raspbery Pi Nicolas Saenz Julienne
2019-05-20 10:51   ` Viresh Kumar
2019-05-20 12:30   ` Stefan Wahren
2019-05-20 10:51 ` Viresh Kumar [this message]
2019-05-21 12:02   ` [RFC v2 0/5] cpufreq support for the Raspberry Pi Nicolas Saenz Julienne

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