Implement BIO_DELETE command with MMC and SD erase commands.

Erase operation gives card's logic information about unused areas to help it
implement wear-leveling with lower overhead comparing to usual writing.
Erase is much faster then write and does not depends on data bus speed.
Also as result of hitting in-card write logic optimizations I have measured
up to 50% performance boost on writing undersized blocks into preerased areas.

At the same time there are strict limitations on size and allignment of erase
operations. We can erase only blocks aligned to the erase sector size and
with size multiple of it. Different cards has different erase sector size
which usually varies from 64KB to 4MB. SD cards actually allow to erase
smaller blocks, but it is much more expensive as it is implemented via
read-erase-write sequence and so not sutable for the BIO_DELETE purposes.

Reviewed by:	imp@

0 files changed, 0 insertions, 0 deletions