[+ clock maintainers]

On 6/13/22 6:17 AM, Andre Przywara wrote:

On Sun, 12 Jun 2022 23:09:07 +0200
Jernej Škrabec [off-list ref] wrote:

Hi Samuel,

quoted

Dne torek, 31. maj 2022 ob 06:50:35 CEST je Samuel Holland napisal(a):

quoted

This series is preparation for converting the PRCM MFD and legacy clock
drivers to a CCU clock driver.

May I ask what the purpose of this exercise is? So if I understand
correctly, then it's about to convert the sun8i-a23-prcm MFD driver and
its children to a single "modern style" CCU clock driver, with its opaque
DT node?

Yes, the purpose is to finish the conversion that was started six years
ago[1][2], and eventually delete drivers/clk/sunxi.

[1]: https://git.kernel.org/torvalds/c/78a9f0dbcd60
[2]: https://git.kernel.org/torvalds/c/2c89ce4f4b19

If that changes the compatible strings or the references to the clock
providers (and I guess it would need to?), then this would mean an
incompatible change. Which also means we would need to keep the old code
around, to maintain compatibility with "old" DTs? So what is the win then?
Now we have *two* clock drivers, for the same device, which need
maintenance and testing.

We already have two drivers for the PRCM. ccu-sun8i-r, which is already built in
to all MACH_SUN8I kernels, was originally intended to support A31/A23/A33, but
nobody ever implemented it. See the comment in the binding header:

    /* 8 is reserved for CLK_APB0_W1 on A31 */

The benefits of conversion are:
 - U-Boot does not have to add support for an already-deprecated clock framework.
 - Users who know they have a recent devicetree can disable CLK_SUNXI.
 - Eventually we can disable CLK_SUNXI and delete drivers/clk/sunxi.

Yes, we need to keep the old code for several years to support existing
devicetrees. That is exactly why I want to do the conversion as soon as
possible: to get that clock started now.

So can you confirm that this will be a breaking change?

Yes, just like the other half of the CCU conversion was.

quoted

The platform SMP code references the PRCM

quoted

node to map its MMIO space, which will break when the PRCM node is
removed/replaced.  

Why can't we just leave old platform code? If older dtb file is used, it would 
still work. Actually, isn't trivial to support new CCU binding too, just by 
including new CCU compatible string? IIUC new CCU node will have same address 
as current PRCM node.

Yes, I could add the new compatible. I was trying to avoid adding more code and
more complexity to code that appeared to be unused in the first place.

This aims for a similar direction, though in this case the alternative
(PSCI) predates the sunxi specific method in the kernel support. Can we
just deprecate this code, maybe issue a warning, with the hint to update
the bootloader (which might not be possible for some devices)?

Since mainline U-Boot provides PSCI, I assume the purpose of this code was to
support the vendor bootloader blob. And the threads adding this code[3][4]
confirm that. In that case, users would have to be using a DTB shipped with the
kernel, not the one provided by the bootloader. So if we change the devicetree,
we have to change the code, too.

Regards,
Samuel

[3]: https://lore.kernel.org/lkml/20131110100312.GI26440@lukather/ (local)
[4]: https://lore.kernel.org/lkml/1426649042-30547-1-git-send-email-wens@csie.org/ (local)

Cheers,
Andre

quoted

Best regards,
Jernej

quoted

Since PSCI has been available for 7+ years, instead of trying to deal
with the migration, I think it's safe to just delete this code.


Samuel Holland (3):
  ARM: sunxi: Remove A31 and A23/A33 platform SMP code
  ARM: dts: sunxi: Remove obsolete CPU enable methods
  dt-bindings: arm: Remove obsolete CPU enable methods

 .../devicetree/bindings/arm/cpus.yaml         |   2 -
 arch/arm/boot/dts/sun6i-a31.dtsi              |   1 -
 arch/arm/boot/dts/sun8i-a23-a33.dtsi          |   1 -
 arch/arm/mach-sunxi/Makefile                  |   1 -
 arch/arm/mach-sunxi/platsmp.c                 | 194 ------------------
 5 files changed, 199 deletions(-)
 delete mode 100644 arch/arm/mach-sunxi/platsmp.c

-- 
2.35.1

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