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SubjectRe: [PATCH 2/2] clk: Add Fixed MMIO clock driver
Quoting Janek Kotas (2018-11-30 00:52:16)
> We have a single register in a fixed location which contains
> the frequency of the main system clock.
> This allows us to use the same image in emulation, FPGA
> and simulation without any changes.
> We usually don’t use a full bootloader, just a simple wrapper,
> which initializes the necessary stuff and jumps to the kernel.
> So the hardware team has decided to throw a frequency register in there?
> Alright! Does that fixed rate clk generate its fixed rate from some
> other clk? I’m curious if this fixed rate clk has a parent source.
> It depends, in simulation and emulation we can just generate
> a clock source with a given frequency.
> On FPGA it’s usually an external oscillator, sometimes a fixed PLL.
> The driver is not intended to be used in full, complex SoCs.

Ok, sounds like it isn't worth modeling this then.

> It would also be good to make sure that any clks registered from this
> driver can't be populated from regions of memory like DDR. Can you
> confirm? I think it will fail, but it would be worth checking

Please try this.

> Yes I'd prefer a platform driver unless there's some reason it can't be
> done. We may need to have both in case this needs to be populated very
> early, but if that isn’t the case then just a platform driver for now.
> I played with it a bit, and it and it looks like I need both.
> We use this clock source with some of our components,
> and for some of them the platform driver was initialized too late.

Ok. So do both then.

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