globalvar: make globalvar functions more consistent ...

Similar to the device parameter functions also make the globalvar
functions more consistent. This also adds support for readonly
globalvars and changes several existing globalvars which should
really be readonly to readonly.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

mtd: when creating bitflips the offset has to be page aligned ...

mtd_peb_create_bitflips() assumes the offset is page aligned. Enforce
this and in the nand_bitlfip command print a warning if it's not
aligned.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

mtd: create bitflips in the correct page ...

In mtd_peb_create_bitflips() buf always points to the first page in a
block. If we want to create bitflips in other pages we have to add the
offset into the block.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

mtd: peb: Fix format specifier ...

The correct format specifier for size_t is %zu. Use it.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

mtd: peb: fix usage of uninitialized variable ...

'read' is used in an error message but never assigned a value to. Remove
the variable.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

commands: Create nand_bitflip command ...

This adds a command to flip bits in a Nand flash. This is useful for
testing purposes to check if flipped bits are corrected and if the
driver returns the correct number of bitflips.

The command writes a configurable number of bitflips to a single Nand
page. If the -r option is not given the results are reproducible, so
calling the same command twice will revert the bitflips.

The command uses the raw read/write Nand operations which are probably
less tested than the regular read/write operations, so the command may
produce surprising results.

As of writing the command has been tested with the GPMI Nand driver and
the imx-nand driver with fixes posted.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

mtd: Introduce mtd-peb API ...

Code which properly wants to handle Nand flash has to work
in a block based way since blocks are the entities that are erased or
may become bad. The regular mtd API works based on offsets in the device
which introduces unhandy 64bit arithmetics and the requirement to align
buffers to blocks.
This introduces the mtd peb API (PEB for physical Erase Block) which
allows the users to work in a block oriented way. The API is heavily
inspired by the UBI IO layer and in fact can replace parts thereof
later.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>