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

From: Stefan Wahren
Date: Tue May 21 2019 - 08:44:00 EST

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:
> - 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.