Hi Markus and Wolfgang,
On 03/19/2014 10:40 AM, Markus Niebel wrote:
Am 19.03.2014 15:44, wrote Wolfgang Denk:
Dear Eric Nelson,
In message <5329a80b.9020...@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 ...
It seems to me that if you're resorting to using un-formatted
storage space to store a broken data structure (the BMP header),
you could just write it at an offset +2.
The BMP support is pretty difficult to use anyway (only supports
BMPV3 headers), so asking the user to know about the offset doesn't
seem onerous.
Also note that the patch I submitted recently handles the case
for gzipped files for those using cfb_console.
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.
IMHO, this seems like overkill. Should we also prevent over-writing
the stack or heap?
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.
Note that "sata read/write" and "usb read/write" have the same issues.
Regards,
Eric
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