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

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Date:   Sun, 18 Aug 2019 00:22:49 +0800
From:   Chuanhong Guo <gch981213@...il.com>
To:     Oleksij Rempel <fishor@....net>
Cc:     Rob Herring <robh@...nel.org>,
        "open list:COMMON CLK FRAMEWORK" <linux-clk@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:MIPS" <linux-mips@...r.kernel.org>,
        "open list:STAGING SUBSYSTEM" <devel@...verdev.osuosl.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>,
        James Hogan <jhogan@...nel.org>,
        John Crispin <john@...ozen.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Weijie Gao <hackpascal@...il.com>, NeilBrown <neil@...wn.name>
Subject: Re: [PATCH v2 4/6] dt: bindings: add mt7621-pll dt binding documentation

Hi!

On Sat, Aug 17, 2019 at 11:40 PM Oleksij Rempel <fishor@....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.

> 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.
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

Regards,
Chuanhong Guo