Re: [PATCH 01/12] dt-bindings: clock: mediatek: document clk bindings for mediatek mt7986 SoC

[Sam Shih]

Hi,

Sorry for the late reply,I have prepared v2 patches, but for some of your suggestions, I think
it is a bit difficult to apply to our drivers.


On Fri, 2021-07-30 at 14:30 +0800, Chen-Yu Tsai wrote:
> On Fri, Jul 30, 2021 at 2:01 PM Sam Shih <sam.shih@xxxxxxxxxxxx>
> wrote:
> > 
> > Hi,
> > 
> > On Mon, 2021-07-26 at 17:20 +0800, Chen-Yu Tsai wrote:
> > > Furthermore, based on the driver patch and the fact that they
> > > share
> > > the
> > > same compatible string, it seems you shouldn't need to have two
> > > compatible
> > > strings for two identical hardware blocks. The need for separate
> > > entries
> > > to have different clock names is an implementation detail. Please
> > > consider
> > > using and supporting clock-output-names.
> > > 
> > > Also, please check out the MT8195 clock driver series [1]. I'm
> > > guessing
> > > a lot of the comments apply to this one as well.
> > > 
> > > Regards
> > > ChenYu
> > > 
> > > [1]
> > > 
https://urldefense.com/v3/__https://lore.kernel.org/linux-mediatek/20210616224743.5109-1-chun-jie.chen@xxxxxxxxxxxx/T/*t__;Iw!!CTRNKA9wMg0ARbw!29pb4TJiGHLvLbYJgDB2Dhf8Mpw5VU8zV-W3NrMan_RPQrtWT2EdRTyyjWpu0nZE$
> > > 
> > > 
> > 
> > I have organized your comments in "Mediatek MT8195 clock support"
> > series into the following list, reply to your here:
> > 
> > > dt-binding: Move the not-to-be-exposed clock to driver directory
> > > or
> > > simply left out
> > 
> > Okay, thanks for your comment, I will update this in the next patch
> > set
> 
> See the following file for an example:
> 
> 

> https://urldefense.com/v3/__https://elixir.bootlin.com/linux/latest/source/drivers/clk/sunxi-ng/ccu-sun50i-a64.h__;!!CTRNKA9wMg0ARbw!3--UEpFFGeZ_WTCaWsj_9vbbb4SSE1vPCILFleThzpa1nq7mveFfQMDqbacdT5I6$ 
> 
> drivers would not be able to use the non-exported intermediate
> clocks.
> 
Thanks, I well delete some clocks that are not expected to be use in
device tree.

> > > describe some of the clock relations between the various clock
> > > controllers
> > 
> > I have checked the files in
> > "Documentation/devicetree/bindings/arm/mediatek", It seems that all
> > MediaTek SoC clocks are simply described by each controller, like
> > "mediatek,infracfg.txt" and "mediatek,topckgen.txt", and those
> > document
> > only include compatible strings information and examples.
> > Can we insert the clock relationship of MT7986 directlly in common
> > documents?
> 
> What I meant was that since each clock controller hardware block has
> one or many clock inputs, these should be described in the binding
> as required "clocks" and "clock-names" properties.
> 
> So it's not about describing the actual relationship or clock tree,
> but just having the inputs accurately described.
> 
> > Or we should add a new "mediatek,mt7986-clock.yaml" and move
> > compatible
> > strings information and example to this file, and insert clock
> > relationship descriptions to this file? Wouldn’t it be strange to
> > skip
> > existing files and create a new one?
> 
> I think that is a question for the device tree binding maintainer,
> Rob.
> At least for Mediatek stuff, there seem to be many separate files.
> 
> > > external oscillator's case, the oscillator is described in the
> > > device
> > > tree
> > 
> > Yes, we have "clkxtal" in the DT, which stands for external
> > oscillator,
> > All clocks in apmixedsys use "clkxtal" as the parent clock
> 
> So for the apmixedsys device node, it would at least have something
> like:
> 
>     clocks = <&clkxtal>;
>     clock-names = "xtal";
> 
> For topckgen, since it has xtal and some PLLs from apmixedsys as
> inputs:
> 
>     clocks = <&clkxtal>, <&apmixedsys CLK_ID_PLLXXX>, <&apmixedsys
> CLK_ID_PLLYYY>;
>     clock-names = "xtal", "pllXXX", "pllYYY"
> 
> The above is just an example. You should adapt it to fit your
> hardware
> description. And the bindings should describe what is required. Note
> that the clock names used here are local to this device node. They do
> not need to match what the clock driver uses for the global name. So
> just go with something descriptive.
> 
> The point is, cross hardware block dependencies should be clearly
> described
> in the device tree, instead of implicitly buried in the clock
> drivers.
> 

Make cross hardware block dependencies clearly described in the device
tree seems unsuitable between "topck" and "infra" block of mt7986.

In your example, passing "clkxtal" from the device tree seems ok. Even
for topckgen, passing "clkxtal", "pllXXX", "pllYYY" from the device
tree and using these clocks as the parent clock of topckgen also seems
to work. It is feasible because it is not much clock between these two
hardware blocks.

But for the clock releationship between "topckg" and "infra", they are
very complicated in hardware design. There are dozens of clocks and
interact with each other. If we want to describe these relationships in
the device tree, we need to use a big array inside the device tree and
make device tree looks very messy. Therefore, our previous method of
writing a clock driver is to use the global clock and descripbe the
clock releationship inside the clock driver.

               ______   ________    ________
    clkxtal --|      |  |       |.x.|       |
              |apmix.|--| topck |.x.| infra |
              |      |--|       |.x.|_______|
              |      |  |       |   ________
              |______|  |       |--|        |
                        |       |--| ethsys |
                        |_______|  |________|

Maybe we should keep the clock relationship in our clock driver like
the previous mediatek clock drivers.


> > > Dual license please (and the dts files).
> > 
> > Okay, thanks for your comment, I will update this in the next patch
> > set
> > 
> > > Why are this and other 1:1 factor clks needed? They look like
> > > placeholders. Please remove them.
> > 
> > Okay, thanks for your comment, I will update this in the next patch
> > set
> 
> Ideally the clock driver would use the device tree to get local
> references
> for this, but that is going to require some rework to Mediatek's
> common
> clock code.
> 

To transfer the clock relationship through the device tree, it is
necessary to make modifications to the common part of the mtk clock
driver that has been merged, and may also modify other mediatek clock
drivers.

Let's move to the source code:
	
apmixedsys {
    ...
}
	
topckgen {
    ...
    clocks = ... , <&apmixedsys NET2PLL> , ... ;
    clock-names = ... , "net2pll" , ... ;
}

char *parent_name;
    for each clk in <device_tree_node>:
        parent_name = __clk_get_name(of_clk_get(np, i))
	
(armada-37xx-tbg.c use this method to get global name of parent clock)

Ideally, we should use the parent_name variable above to create a
clock, But mtk_fixed_factor expects input const strings
	
void mtk_clk_register_factors(const struct mtk_fixed_factor *clks, ...)
	
struct mtk_fixed_factor {
    ...
    const char *name;
    const char *parent;
    ...
};

So we still need to use pre-defined clock name in static const clock
table even we can get clock name as variable from device tree.


static const struct mtk_fixed_factor top_divs[] __initconst = {
    ...
    FACTOR(CK_TOP_NET2_D4_D2, "net2_d4_d2", "net2pll", 1, 8),
    FACTOR(CK_TOP_NET2_D3_D2, "net2_d3_d2", "net2pll", 1, 2),
    ...
}



> > > Merge duplicate parent instances
> > 
> > We have considered this in the MT7986 basic clock driver, but I
> > will
> > check again. If corrections are needed, I will make changes in the
> > next
> > patch set.
> > 
> > > Leaking clk_data if some function return fail
> > 
> > Okay, thanks for your comment, I will update this in the next patch
> > set
> > 
> > > This file contains four drivers. They do not have depend on each
> > > other, and do not need to be in the same file. Please split them
> > > into
> > > differen files and preferably different patches
> > 
> > Okay, thanks for your comment, I will separate those clock drivers
> > in
> > the next patch set
> > 
> > > Is there any particular reason for arch_initcall
> > 
> > We have considered this in MT7986 basic clock driver, and use
> > CLK_OF_DECLARE instead of arch_initcall.
> 
> Having to sequence clock registration manually is likely a symptom of
> inadequate clock dependency handling. So if the drivers are only
> using
> global clock names to describe parents, what happens is that even if
> the parent isn't in the system yet, the registration is allowed to
> succeed. However since the parent clock isn't available yet, any
> calculations involving it, such as calculating clock rates, will
> yield invalid results, such as 0 clock rate.
> 
> > Another question:
> > Should the clock patches in "Add basic SoC support for MediaTek
> > mt7986"
> > need to be separated into another patch series, such as MT8195
> > "Mediatek MT8195 clock support" ?
> 
> Nope. The MT8195 team seems to be splitting things up by module, with
> the device tree being its own separate module. Ideally you want to
> send
> drivers along with the related device tree changes, so people
> reviewing
> can get a sense of how things work. And if the hardware is publicly
> available, people can actually test the changes. We can't do that if
> the
> device tree changes aren't bundled together.
> 
OK, I will keep clock patches and basic part patches in the same series
(patches v2)


Regards,
Sam
Thanks, I will delete some clocks that are not expected to b