linux-kernel - Re: [RFC v2 3/5] clk: bcm2835: use firmware interface to update pllb

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Message-ID: <6383b357-3f7e-f031-f59f-61c598e44763@i2se.com>
Date:   Tue, 21 May 2019 14:40:58 +0200
From:   Stefan Wahren <stefan.wahren@...e.com>
To:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Florian Fainelli <f.fainelli@...il.com>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        bcm-kernel-feedback-list@...adcom.com,
        Eric Anholt <eric@...olt.net>
Cc:     linux-arm-kernel@...ts.infradead.org, ptesarik@...e.com,
        sboyd@...nel.org, viresh.kumar@...aro.org, mturquette@...libre.com,
        linux-pm@...r.kernel.org, rjw@...ysocki.net,
        linux-kernel@...r.kernel.org, linux-rpi-kernel@...ts.infradead.org,
        linux-clk@...r.kernel.org, mbrugger@...e.de, ssuloev@...altech.com
Subject: Re: [RFC v2 3/5] clk: bcm2835: use firmware interface to update pllb

Hi Nicolas,

On 20.05.19 14:11, Stefan Wahren wrote:
> Hi Nicolas,
>
> the following comments applies only in case Eric is fine with the whole
> approach.
>
> On 20.05.19 12:47, Nicolas Saenz Julienne wrote:
>> Raspberry Pi's firmware, which runs in a dedicated processor, keeps
> maybe we should clarify that the firmware is running in the VPU
>> track of the board's temperature and voltage. It's resposible for
>> scaling the CPU frequency whenever it deems the device reached an unsafe
>> state. On top of that the firmware provides an interface which allows
>> Linux to to query the clock's state or change it's frequency.
> I think this requires a separate update of the devicetree binding.
>> Being the sole user of the bcm2835 clock driver, this integrates the
>> firmware interface into the clock driver and adds a first user: the CPU
>> pll, also known as 'pllb'.
> Please verify that the kernel still works (and this clock driver probe)
> under the following conditions:
>
> - CONFIG_RASPBERRYPI_FIRMWARE=n
> - CONFIG_RASPBERRYPI_FIRMWARE=m
> - older DTBs without patch #1
i thought about this and the case this driver would return
-EPROBE_DEFER. The clock driver is too essential for doing such a thing.
So i think the best solution would be to move these changes into a
separate driver which should be register by the clock driver (similiar
to vchiq). This also avoid the need of a new device tree binding.