Adding subpage support to NAND driver -- backwards compatibility concerns

Ben Shelton
2015-04-22T17:30:14Z

Hi all,

We're currently carrying a patch out of tree to add subpage read and
write support to the pl353_nand driver. Xilinx is currently working to
mainline this driver; see

http://www.spinics.net/lists/devicetree/msg76307.html

We'd like to upstream our patch, but my concern is that UBIFS behaves
differently when it knows that the flash device supports subpages. I
have a couple of questions related to that:

- I know from experience that bad things happen when you use a kernel
without subpage support with an UBIFS filesystem that was formatted
with subpage support. Is it safe to do the opposite (kernel with
subpage support / UBIFS filesystem formatted without subpage support)?

- Assuming that it isn't safe, what's the best way to add subpage
support to this driver in an upstreamable way / without breaking
people? Would it be sufficient to add subpage support as a Kconfig
option that's disabled by default with a strongly-worded message
describing the consequences of enabling it?

Thanks,
Ben