In some cases the card needs to be returned to standby mode from data
transfer mode. This is done using CMD7 command, which does not receive
any response in this case.
MMC_RSP_BITS helper function had a hack that it flipped word order in
the response, assuming that response size is 4 words. This hack does not
work for responses which are not 4 words long (such as the SWITCH_FUNC
response, which is 64 words long).
This change removes the hack and the matching word order reversal code
in sdmmc driver.
SDMMC hardware treats all buffers as aligned, and ignores 2 LSBs of
addresses written into DMA descriptors. Previously SDMMC host driver
assumed that data buffers passed from SDDMC command layer would be
aligned. However alignment checks were never implemented in the command
layer, as were the checks that the buffer coming from the application
would be in DMA capable memory. Most of the time this was indeed true.
However in some cases FATFS library can pass buffers offset by 2 bytes
from word boundary. “DMA capable” restriction may be broken if pSRAM
support is used.
This change adds buffer checks to the SDMMC host driver (alignment and
DMA capability), so that the host layer will error out for incompatible
buffers. In SDMMC command layer, a check is added to read and write
functions. If an incompatible buffer is passed from the application, new
buffer (512 bytes size) is allocated, and the transfer is performed
using {READ,WRITE}_SINGLE_BLOCK commands.
