Am 19.03.2014 15:44, wrote Wolfgang Denk:
Dear Eric Nelson,
In message 5329A80B.9020908@boundarydevices.com you wrote:
short question to the usage of the mmc command (and also the mmc driver API): is it intended that mmc read / write may fail when the supplied address in RAM is not aligned?
If not intended, it is known.
I consider this a known bug.
ARMV7 will give output like this:
U-Boot > mmc read 12000002 44 44
Why would you want to do this?
For example, BMP images require loading on a +2 aligned address due to their stupid header format. I ran into this before myself: it is impossible to match both the alignment reuqirements of the bmp command and the mmc read command at the same time. One must manually copy the memory ragen again. This is a plain, stupid bug.
Exactly here it popped up ...
Special commands inside the mmc drivers and in env_mmc implement the alignment magic. Shouldn't the mmc do the magic (and if neccesarry provide help using temp buffers if needed) so that all users outside can read / write without caring for special cases?
Is there a use case here? There are plenty of memory addresses that won't work with commands like "mmc read".
env_mmc needs to care for cache aligned buffers - This was fixed some time ago for the redundant env case
"mmc read" and "mmc write" are operations that work on character buffers, like all other file IO ops. These should not require any specific alignment.
Is it worth **any** code to try and catch them?
Definitely yes.
So just as an idea - we could use a bounce buffer for mmc_bwrite / mmc_bread for the unaligned case. Is definitely slow but should work.
Best regards,
Wolfgang Denk