Amlogic 32-bit Meson SoC SDHC MMC controller driver

[Martin Blumenstingl]

Hello,

this is the first non-RFC version of the driver for the Amlogic "SDHC"
MMC controller found on Meson6, Meson8, Meson8b and Meson8m2 SoCs.

The public S805 (Meson8b) datasheet has some documentation starting on
page 74: [0]

It's performance is still not as good as the driver from Amlogic's 3.10
kernel, but it does not corrupt data anymore (as RFC v1 did).

Special thanks to the people who supported me off-list - you are
amazing and deserve to be mentioned here:
- Xin Yin who helped me fix two more write corruption problems. I am
  hoping that he will reply with Reviewed-by, Tested-by and Bug-fixed-by
- Jianxin Pan for sharing some of the internal workings of this MMC
  controller with me
- Wei Wang for spotting the initial write corruption problem and helping
  test this driver on his board. I have his permission to add his
  Tested-by (off-list, he's Cc'ed so if there's any problem he can speak
  up)


Changes since RFC v1 at [1]:
- don't set MESON_SDHC_MISC_MANUAL_STOP to fix one of three write
  corruption problems. the out-of-tree 3.10 "reference" driver doesn't
  set it either
- check against data->flags instead of cmd->flags when testing for
  MMC_DATA_WRITE as spotted by Xin Yin (many thanks!). This fixes
  another write corruption problem
- clear the FIFOs after successfully transferring data as suggested by
  Xin Yin (many thanks!). This is what the 3.10 driver did and fixes yet
  another write corruption problem
- integrate the clock suggestions from Jianxin Pan so the driver is now
  able to set up the clocks correctly for all known cases. documentation
  is also added to the patch description. Thank you Jianxin for the
  help!
- set the correct max_busy_timeout as suggested by Jianxin Pan (thanks!)
- convert the dt-bindings to .yaml (which is why I didn't add Rob's
  Reviewed-by)
- switch to struct clk_parent_data as part of newer common clock
  framework APIs to simplify the clock setup
- dropped CMD23 support because it seems to hurt read and write
  performance by 10-20% in my tests. it's not clear why, but for now we
  can live without this.
- use devm_platform_ioremap_resource instead of open-coding it


[0] https://dn.odroid.com/S805/Datasheet/S805_Datasheet%20V0.8%2020150126.pdf
[1] https://patchwork.kernel.org/cover/11035505/


Martin Blumenstingl (2):
  dt-bindings: mmc: Document the Amlogic Meson SDHC MMC host controller
  mmc: host: meson-mx-sdhc: new driver for the Amlogic Meson SDHC host

 .../bindings/mmc/amlogic,meson-mx-sdhc.yaml   |   64 +
 drivers/mmc/host/Kconfig                      |   14 +
 drivers/mmc/host/Makefile                     |    1 +
 drivers/mmc/host/meson-mx-sdhc.c              | 1174 +++++++++++++++++
 4 files changed, 1253 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/mmc/amlogic,meson-mx-sdhc.yaml
 create mode 100644 drivers/mmc/host/meson-mx-sdhc.c

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2.24.0