Re: [PATCH 01/12] dt-bindings: clock: mediatek: document clk bindings for... | linux-arm-kernel

quoted

On Fri, 2021-08-13 at 14:15 +0800, Chen-Yu Tsai wrote:
On Fri, Aug 13, 2021 at 1:22 PM Sam Shih [off-list ref]
wrote:
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 [off-list ref]
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@mediatek.com/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.
Are you saying that some clocks in topck have inputs from infra?
If so, then that's a nasty circular dependency to deal with.
Sorry I didn't express it very clearly, I mean that there are many
clock　connections between "ckgen" and "infra" (unlike apmixedsys and
ckgen). Although most of the clocks in "infra" is derived from "ckgen".
But if we want to use the device tree, we will need to pass dozens of
clocks.

And to be fair, many Mediatek device tree bindings already take a
large
number of clocks, so I think adding a few more isn't too bad.
It will become something like:

clocks = <&topckgen CLK_TOP_NFI1X>,<&topckgen
CLK_TOP_USB_EQ_RX250M>,<&topckgen CLK_TOP_USB_TX250M>,<&topckgen
CLK_TOP_USB_LN0_CK>,<&topckgen CLK_TOP_USB_CDR_CK>,<&topckgen
CLK_TOP_SPINFI_BCK>,<&topckgen CLK_TOP_I2C_BCK>,<&topckgen
CLK_TOP_PEXTP_TL>,<&topckgen CLK_TOP_EMMC_250M>,<&topckgen
CLK_TOP_EMMC_416M>,<&topckgen CLK_TOP_F_26M_ADC_CK>,<&topckgen
CLK_TOP_SYSAXI>,<&topckgen CLK_TOP_NETSYS_WED_MCU>,<&topckgen
CLK_TOP_NETSYS_2X>,<&topckgen CLK_TOP_SGM_325M>,<&topckgen
CLK_TOP_A1SYS>,<&topckgen CLK_TOP_EIP_B>,<&topckgen
CLK_TOP_F26M>,<&topckgen CLK_TOP_AUD_L>,<&topckgen
CLK_TOP_A_TUNER>,<&topckgen CLK_TOP_U2U3_REF>,<&topckgen
CLK_TOP_U2U3_SYS>,<&topckgen CLK_TOP_U2U3_XHCI>,<&topckgen
CLK_TOP_AP2CNN_HOST>,<&topckgen CLK_TOP_NFI1X_SEL>,<&topckgen
CLK_TOP_SPINFI_SEL>,<&topckgen CLK_TOP_SPI_SEL>,<&topckgen
CLK_TOP_SPIM_MST_SEL>,<&topckgen CLK_TOP_UART_SEL>,<&topckgen
CLK_TOP_PWM_SEL>,<&topckgen CLK_TOP_I2C_SEL>,<&topckgen
CLK_TOP_PEXTP_TL_SEL>,<&topckgen CLK_TOP_EMMC_250M_SEL>,<&topckgen
CLK_TOP_EMMC_416M_SEL>,<&topckgen CLK_TOP_F_26M_ADC_SEL>,<&topckgen
CLK_TOP_DRAMC_SEL>,<&topckgen CLK_TOP_DRAMC_MD32_SEL>,<&topckgen
CLK_TOP_SYSAXI_SEL>,<&topckgen CLK_TOP_SYSAPB_SEL>,<&topckgen
CLK_TOP_ARM_DB_MAIN_SEL>,<&topckgen CLK_TOP_ARM_DB_JTSEL>,<&topckgen
CLK_TOP_NETSYS_SEL>,<&topckgen CLK_TOP_NETSYS_500M_SEL>,<&topckgen
CLK_TOP_NETSYS_MCU_SEL>,<&topckgen CLK_TOP_NETSYS_2X_SEL>,<&topckgen
CLK_TOP_SGM_325M_SEL>,<&topckgen CLK_TOP_SGM_REG_SEL>,<&topckgen
CLK_TOP_A1SYS_SEL>,<&topckgen CLK_TOP_CONN_MCUSYS_SEL>,<&topckgen
CLK_TOP_EIP_B_SEL>,<&topckgen CLK_TOP_PCIE_PHY_SEL>,<&topckgen
CLK_TOP_USB3_PHY_SEL>,<&topckgen CLK_TOP_F26M_SEL>,<&topckgen
CLK_TOP_AUD_L_SEL>,<&topckgen CLK_TOP_A_TUNER_SEL>,<&topckgen
CLK_TOP_U2U3_SEL>,<&topckgen CLK_TOP_U2U3_SYS_SEL>,<&topckgen
CLK_TOP_U2U3_XHCI_SEL>,<&topckgen CLK_TOP_DA_U2_REFSEL>,<&topckgen
CLK_TOP_DA_U2_CK_1P_SEL>,<&topckgen CLK_TOP_AP2CNN_HOST_SEL>;

I don't think this is okay in device tree...

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),
    ...
}
Right. I'm not asking you to do this right away. This will end up
being
a long migration over multiple releases. But it makes sense to get
the
device tree bindings sorted out first.

I believe the solution is to move to `struct clk_parent_data` to
replace
the pure strings. New internal APIs for the Mediatek clock driver
would
need to be added, and all the drivers slowly migrated over. Probably
also
a good time to migrate to clk_hw_*_register.

ChenYu

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
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