[Qemu-devel] [RFC 0/7] Convert SD card model to AIO

[Igor Mitsyanko <i.mitsyanko@gmail.com>]

This is an initial attempt to change our SD card model to use asynchronious
input/output API instead of synchronious one. This will require converting of
every user also. Right now I've converted only PL181 model, and I'll wait
for some feedback on taken approach before I'll continue with other users.

New async SD interface is built on two callbacks:
1 Callback which models arrival of start bit on DAT line from card (start bit)
2 Callback modeling deasserting of DAT0 line by card when it has finished
programming data (data busy end)

This is based on SD card specification.
Start bit is issued for every new block of data coming from card.
DAT0 line is kept low by card to signal busy state, while data block is being
programmed by card and it can't receive new data.

Furthermore, I decided to drop data buffering on SD controller side. We already
have two buffers in SD card model, no need to have another one in controller model.
We can avoid intermediate copying from card's buffer to controller's buffer, and
read/write directly from card.

Tested by running this Fedora image 
https://fedoraproject.org/wiki/Architectures/ARM/F18/Versatile_Express
on versatile board.

Igor Mitsyanko (7):
  sd.c: introduce AIO related members in SD state
  sd.c: introduce variable for trekking valid data
  sd.c: introduce "start bit" and "busy deasserted" callbacks
  sd.c: use callbacks as a flag to use async IO
  sd.c: introduce async read operation
  sd.c: introduce async write interface
  pl181.c: convert to async IO SD card interface

 hw/sd/omap_mmc.c    |   6 +-
 hw/sd/pl181.c       | 302 +++++++++++++++++++++++++++++++++-------------------
 hw/sd/pxa2xx_mmci.c |   2 +-
 hw/sd/sd.c          | 272 ++++++++++++++++++++++++++++++++++++++++++----
 hw/sd/sdhci.c       |   4 +-
 include/hw/sd.h     |   3 +-
 6 files changed, 449 insertions(+), 140 deletions(-)

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1.8.1.4