[RFC 0/2] Add support for Meson MX "SDIO" MMC driver

Martin Blumenstingl martin.blumenstingl at googlemail.com
Sat May 6 10:18:55 PDT 2017

This is the successor to Carlo Caione's "Add support for Amlogic Meson
MMC driver" series (v5) from [0].

I would like you to specifically review:
- whether I've (ab)used the MMC framework properly (as this is my first
  "larger" contribution to an MMC driver)
- I think I have improved the locking compared to Carlo's version,
  however I'd still like feedback on whether this looks sane now or if I
  can improve that even further

(notable) changes since Carlo's latest version are:
- renamed the driver to meson-mx-sdio (Amlogic's reference kernel calls
  the driver "aml_sdio" as there is a second MMC controller in these SoCs
  which they call the "SDHC controller"). do the same with our driver to
  avoid confusion once we add support for the second controller (which uses
  a completely different register layout)
- add support for the internal "mux" in this MMC controller (which allows
  connecting up to three devices to the the controller - at the cost of
  performance though since the controller can only process one request at
  a time). The driver registers a new device for each sub-node, which is
  then fed into the MMC framework to allow per-slot configuration using
  devicetree (see the example in the documentation)
- use the common clock framework internally for managing the MMC clock
  (there is a fixed-factor clock in the controller which takes clk81 as
   input and divides it's clock by two and a divider clock which takes
   the result from the fixed-factor clock as input)
- support the regulators provided by the MMC framework
- support for GPIO-based card-detection and read-only-detection through
  the MMC framework
- use of the <linux/bitfield.h> FIELD_PREP and FIELD_GET macros where it
  make sense (and thus the code easier to read)
- re-worked locking (based on the locking in dw_mmc as that also provides
  multiple "MMC slots")

tests done so far:
- reading an OLD 256MiB SD card (which uses only a 1-bit bus) works fine
  (sha1sum of the whole device matches with what I get on my PC's
- reading a somewhat more modern class 10 SD card and putting Arch Linux
  ARM on it (and using that as root file system)
- it successfully detects the RTL8723BS SDIO wifi chip in my device (even
  if the SD card is also enabled)
- reading a 128MiB file from the SD card while scanning wifi networks on
  the RTL8723BS card does not seem to result in any corruption (sha1sum
  of the read file seems to match)
- read speed of my class 10 SD card: ~15MiB/s
- (unfortunately I could NOT test downloading a file over wifi to the SD
  card because the RTL8723BS driver refuses to see any wifi networks, but
  that might be a problem on the RTL8723BS driver side since I don't get
  any error and the driver has just landed a few weeks ago in staging)

[0] http://lists.infradead.org/pipermail/linux-arm-kernel/2016-February/412136.html

Carlo Caione (2):
  dt-bindings: mmc: Document the Amlogic Meson8 and Meson8b SDIO
  mmc: meson-mx-sdio: Add a driver for the Amlogic Meson8 and Meson8b

 .../bindings/mmc/amlogic,meson-mx-sdio.txt         |  50 ++
 drivers/mmc/host/Kconfig                           |  12 +
 drivers/mmc/host/Makefile                          |   1 +
 drivers/mmc/host/meson-mx-sdio.c                   | 978 +++++++++++++++++++++
 4 files changed, 1041 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/mmc/amlogic,meson-mx-sdio.txt
 create mode 100644 drivers/mmc/host/meson-mx-sdio.c


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