[RFC PATCH 0/5] Allwinner MMC firmware clocks implementation

[Icenowy Zheng]

09.08.2016, 19:57, "Andre Przywara" <andre.przywara at arm.com>:
> Hi,
>
> this is a proof-of-concept series to demonstrate the usage of firmware
> driven clocks using the SCPI protocol for Allwinner SoCs.
> This aims to replace the tricky and highly SoC specific clocks drivers
> that every new Allwinner SoC seems to require.
> The idea is to abstract the internal clock specific code by the rather
> generic SCPI interface, which support programming and reading clock
> frequencies in an SoC agnostic manner. The actual clock access can be
> put in firmware, which is by definition SoC specific and thus can
> be easier and much quicker adapted to support a new SoC.
> The SCPI interface requires a mailbox and a shared memory region to
> send commands and receive results.
>
> This series introduces a new mailbox driver, which uses smc instructions
> to trigger a mailbox. This allows the SCPI handlers to live as a runtime
> service component in the existing ARM Trusted Firmware port. Beside
> being able to easily add those handlers to the existing firmware code
> this approach has the advantage of avoiding building, maintaining and
> loading yet another firmware component. The management processor on the
> A64 uses an OpenRISC core, which requires a not fully upstream supported
> toolchain. Also this core can remain free to other tasks, like offloading
> of realtime-sensitive tasks.

Here's a problem...

Although SCPI is a standard, SMC mailbox and ATF clock id is not.

And there's currently no generic clock framework in ATF...

> A future implementation may later revisit this decision, adding a proper
> mailbox driver and implement the SCPI handler on the OpenRISC core, the
> only change needed would be to swap the mailbox node in the DT then.
>
> Another added value is that SCPI brings us sensors and regulators
> support, using this very same interface. All that's needed is to add
> some firmware code to read the THS register or poke the AXP, for
> instance (which ATF does already anyway) and advertise those via a DT
> node. There would be no Linux changes needed for that.
>
> As an example this series adds MMC support on top of the basic support
> bit posted recently [1].
> We use the existing sunxi MMC driver for the purpose of this series,
> although it is known to not fully support the new MMC controller in the
> A64 chip. I found the support sufficient enough to drive SD cards, though.
>
> Patch 1/5 introduces the SMC mailbox driver, while patch 2/5 adds the
> associated DT binding documentation. Patch 3/5 adds the basic SCPI nodes
> to the SoC .dtsi, which patch 4/5 complements with the MMC nodes,
> referencing the new firmware clocks.
> The final patch 5/5 enables the SD card for the two boards which we
> currently support.
>
> This series goes on top of the v4 A64 support series [1], which itself
> is based on v4.8-rc1.
> It allows booting and running a userland from a micro SD card on both
> the Pine64 and the BananaPi M64 board.
> The matching firmware implementation can be found in the allwinner-scpi
> branch here [2]. The clock code in there is probably pretty stupid, but
> works and is good enough to at least serve as a proof-of-concept for this
> new clock approach.
>
> Please have a look and give comments, I am particularily interested in
> how you like this idea. One motiviation is to save the kernel from
> endless variations of clock driver code, also to be able to support
> newer SoCs much easier without having to submit and maintain tedious
> clock patches.
>
> Cheers,
> Andre.
>
> [1]: http://lists.infradead.org/pipermail/linux-arm-kernel/2016-August/447512.html
> [2]: https://github.com/apritzel/arm-trusted-firmware/commits/allwinner-scpi

The code seems to be difficult to extend...
I hope you can make the SMC mailbox a standard interface, and add a common
clock controlling system in the ATF... (And maybe add A64 as part of the reference
implemention) (but I think it may be to difficult to you to make standards and change
reference implemention...)

>
> Andre Przywara (5):
>   mailbox: introduce ARM SMC based mailbox
>   DT: mailbox: add binding doc for the ARM SMC mailbox
>   arm64: dts: sunxi: add SCPI node to sun50i-a64.dtsi
>   arm64: dts: sunxi: add SCPI driven clocks and nodes for A64 MMC
>   arm64: dts: sunxi: add MMC nodes to Pine64 and BPi-M64 .dts
>
>  .../devicetree/bindings/mailbox/arm-smc.txt | 53 ++++++++
>  .../boot/dts/allwinner/sun50i-a64-bananapi-m64.dts | 29 +++++
>  .../arm64/boot/dts/allwinner/sun50i-a64-pine64.dts | 20 +++
>  arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi | 87 +++++++++++++
>  drivers/mailbox/Kconfig | 8 ++
>  drivers/mailbox/Makefile | 2 +
>  drivers/mailbox/smc-mailbox.c | 135 +++++++++++++++++++++
>  7 files changed, 334 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/mailbox/arm-smc.txt
>  create mode 100644 drivers/mailbox/smc-mailbox.c
>
> --
> 2.9.0
>
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