Trivial fix for the issue reported by Guenter here:
https://lore.kernel.org/qemu-devel/5b2dc427-f0db-4332-a997-fe0c82415acd@roeck-us.net/

- Return dummy byte when no card is connected
- Add a test
- Document ssi_transfer()

Since v1:
- Reworded patch #1 description (Alex)
- Removed '_' test method prefix (Alex)

Philippe Mathieu-Daudé (3):
  hw/sd/ssi-sd: Return noise (dummy byte) when no card connected
  tests/functional: Test SPI-SD adapter without SD card connected
  hw/ssi: Document ssi_transfer() method

 include/hw/ssi/ssi.h                      | 14 ++++++++++++++
 hw/sd/ssi-sd.c                            |  4 ++++
 tests/functional/test_riscv64_sifive_u.py | 22 +++++++++++++++++-----
 3 files changed, 35 insertions(+), 5 deletions(-)

-- 
2.49.0