On Tue, Feb 2, 2021 at 10:48 AM Bin Meng <[email protected]> wrote: > > > After command is sent and before card response shows up on the line, > there is a variable number of clock cycles in between called Ncr. > The spec [1] says the minimum is 1 byte and the maximum is 8 bytes. > > Current logic in mmc_spi_sendcmd() has a flaw that it could only work > with certain SD cards with their Ncr being just 1 byte. > > When resp_match is false, the codes try to receive only 1 byte from > the SD card. On the other hand when resp_match is true, the logic > happens to be no problem as it loops until timeout to receive as many > bytes as possible to see a match of the expected resp_match_value. > However not every call to mmc_spi_sendcmd() is made with resp_match > being true hence this exposes a potential issue with SD cards that > have a larger Ncr value. > > Given no issue was reported as of today, we can reasonably conclude > that all cards being used on the supported boards happen to have a 1 > byte Ncr timing requirement. But a broken case can be triggered by > utilizing QEMU to emulate a larger value of Ncr (by default 1 byte > Ncr is used on QEMU). This series fixes such potential spec violation > to improve the card compatibility. > > [1] "Physical Layer Specification Version 8.00" > chapter 7.5.1: Command / Response > chapter 7.5.4: Timing Values > > Changes in v2: > - move the check before the debug output > > Bin Meng (3): > mmc: mmc_spi: Move argument check to the beginning of > mmc_spi_sendcmd() > mmc: mmc_spi: Fix potential spec violation in receiving card response > mmc: mmc_spi: Document the 3 local functions > > drivers/mmc/mmc_spi.c | 74 > ++++++++++++++++++++++++++++++++++++++------------- > 1 file changed, 55 insertions(+), 19 deletions(-) >
Peng, ping?
