linux-phytec-ti

mtd: spi-nor: scale up timeout for full-chip erase

This patch fixes timeout issues seen on large NOR flash (e.g., 16MB
w25q128fw) when using ioctl(MEMERASE) with offset=0 and length=16M. The
input parameters matter because spi_nor_erase() uses a different code
path for full-chip erase, where we use the SPINOR_OP_CHIP_ERASE (0xc7)
opcode.

Fix: use a different timeout for full-chip erase than for other
commands.

While most operations can be expected to perform relatively similarly
across a variety of NOR flash types and sizes (and therefore might as
well use a similar timeout to keep things simple), full-chip erase is
unique, because the time it typically takes to complete:
(1) is much larger than most operations and
(2) scales with the size of the flash.

Let's base our timeout on the original comments stuck here -- that a 2MB
flash requires max 40s to erase.

Small survey of a few flash datasheets I have lying around:

  Chip         Size (MB)   Max chip erase (seconds)
  ----         --------    ------------------------
  w25q32fw     4           50
  w25q64cv     8           30
  w25q64fw     8           100
  w25q128fw    16          200
  s25fl128s    16          ~256
  s25fl256s    32          ~512

From this data, it seems plenty sufficient to say we need to wait for
40 seconds for each 2MB of flash.

After this change, it might make some sense to decrease the timeout for
everything else, as even the most extreme operations (single block
erase?) shouldn't take more than a handful of seconds. But for safety,
let's leave it as-is. It's only an error case, after all, so we don't
exactly need to optimize it.

Signed-off-by: Furquan Shaikh <furquan@google.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>