Re: [PATCH v2 4/6] dt: bindings: add mt7621-pll dt binding documentation

Oleksij Rempel
2019-08-17T18:06:18Z

Am 17.08.19 um 18:22 schrieb Chuanhong Guo:
> Hi!
>
> On Sat, Aug 17, 2019 at 11:40 PM Oleksij Rempel <fishor@gmx.net> wrote:
>
>> In provided link [0] the ralink_clk_init function is reading SYSC_REG_CPLL_CLKCFG0 R/W register.
>> This register is used to determine clock source, clock freq and CPU or bus clocks.
>
> This register should only be changed by bootloader, not kernel. So
> it's read-only in kernel's perspective.
there is no kernel perspective, until you have some kind of privilege
separation. There is only: "i decided not to write on to writeable
register".

>> SYSC_REG_CPLL_CLKCFG1 register is a clock gate controller. It is used to enable or disable clocks.
>> Jist wild assumption. All peripheral devices are suing bus clock.
>
> This assumption is incorrect. When this patchset is applied in
> OpenWrt, I asked the author why there's still a fixed clock in
> mt7621.dtsi, He told me that there's another clock for those unchanged
> peripherals and he doesn't have time to write a clock provider for it.

Can you please provide a link to this patch or email.

> I don't know how many undocumented clocks are there since this piece
> of info is missing in datasheet.
>
>>
>> IMO - this information is enough to create full blown drivers/clk/mediatek/clk-mt7621.c
>
> And this information isn't enough because the assumption above is incorrect :P

Ok, let's assume I accept this not technical argumentation.

We have at least 2 know registers:
SYSC_REG_CPLL_CLKCFG0 - it provides some information about boostrapped
refclock. PLL and dividers used for CPU and some sort of BUS (AHB?).
SYSC_REG_CPLL_CLKCFG1 - a banch of gates to enable/disable clocks for
all or some ip cores. What is probably missing is a set of dividers for
each ip core. From your words it is not document.

With this information the clk driver will provide gate functionality and
a set of hardcoded clocks. With this driver will work part of power
management and nice devicetree without fixed clocks.

--
Regards,
Oleksij