This code was a bit sloppy, would produce a lot of copy-and-paste, and
did not always provide a sensible interface:
* It didn't validate the length for LOCK and the offset for UNLOCK, so
we were essentially discarding half of the user-supplied data and
assuming what they wanted to lock/unlock
* It didn't do very good error checking
* It didn't make use of the fact that this operation works on
power-of-two dimensions
So, rewrite this to do proper bit arithmetic rather than a bunch of
hard-coded condition tables. Now we have:
* More comments on how this was derived
* Notes on what is (and isn't) supported
* A more exendible function, so we could add support for other
protection ranges
* More accurate locking - e.g., suppose the top quadrant is locked (75%
to 100%); then in the following cases, case (a) will succeed but (b)
will not (return -EINVAL):
(a) user requests lock 3rd quadrant (50% to 75%)
(b) user requests lock 3rd quadrant, minus a few blocks (e.g., 50%
to 73%)
Case (b) *should* fail, since we'd have to lock blocks that weren't
requested. But the old implementation didn't know the difference and
would lock the entire second half (50% to 100%)
This refactoring work will also help enable the addition of
mtd_is_locked() support and potentially the support of bottom boot
protection (TB=1).
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
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