*** SUBJECT HERE ***

DesignWare MMC cores have a configurable data bus width of either 16, 32, or 64 bytes. It is possible, and some vendors actually do it, to ship a DW MMC core configured for 32-bit data bus within a 64-bit SoC. In this case the kernel will attempt 64-bit (readq) accesses to certain 64-bit MMIO registers, while the core will expect pairs of 32-bit accesses.

It seems that currently the only register for which the kernel performs 64-bit accesses is the FIFO. The symptom is that the DW MMC core never receives a read on the second half of the register, does not register the datum as being read, and thus not advancing its internal FIFO pointer, breaking further reads. It also seems that this FIFO is only used for small (less than 16 bytes) transfers, which probably means that only some SDIO cards are affected.

Sergey Lisov (2):
devicetree: synopsys-dw-mshc-common: add "fifo-access-32bit" property
dw_mmc: add an option to force 32-bit accesses to 64-bit device
registers

 .../bindings/mmc/synopsys-dw-mshc-common.yaml |   6 +
 drivers/mmc/host/dw_mmc.c                     | 125 +++++++++++++++++-
 drivers/mmc/host/dw_mmc.h                     |   2 +
 3 files changed, 131 insertions(+), 2 deletions(-)

2.38.3