Basically, I divide the eeprom in 8 32-byte slices. Each of it has a
"valid" boolean (combined together into a bitfield) and a jiffies
counter. Eeprom_update_client() is added a new parameter to specify
which slice to update. Code updated accordingly. Finally, the read
function updates only slices that need to be. The code is heavily
inspired from what was done in the CVS driver, of course.

Three additional notes:

1* This fixes a bug in eeprom_update_client()'s refresh condition. We
used to check jiffies before valid, although jiffies are not defined if
valid isn't true. That was already fixed in our CVS driver but for some
reason the fix did not go into 2.6 yet.

2* This also skips the update if the read if out of bounds. I think this
is the thing to do.

3* It can be discussed wether eeprom_update_client() should take two
slice parameters instead of one (start slice, end slice). This would
make things slightly faster when consecutive slices are requested. Maybe
the code would even be clearer. It wasn't done so far because the CVS
driver wouldn't benefit from it (because the EEPROM's contents are split
over several "output" files in that version of the driver) but I'll
probably give it a try in 2.6.