Hi Boris, On Mon, Dec 07, 2015 at 11:25:55PM +0100, Boris Brezillon wrote: > Hello, > > This patchset aims at getting rid of the nand_ecclayout limitations. > struct nand_ecclayout is defining fixed eccpos and oobfree arrays which > can only be increased by modifying the MTD_MAX_ECCPOS_ENTRIES_LARGE and > MTD_MAX_OOBFREE_ENTRIES_LARGE macros. > This approach forces us to modify the macro values each time we add a > new NAND chip with a bigger OOB area, and increasing these arrays also > penalize all platforms, even those who only support small NAND devices > (with small OOB area). > > The idea to overcome this limitation, is to define the ECC/OOB layout > by the mean of two functions: ->eccpos() and ->oobfree(), which will > basically return the same information has those stored in the > nand_ecclayout struct. > > Another advantage of this solution is that ECC layouts are usually > following a repetitive pattern (i.e. leave X bytes free and put Y bytes > of ECC per ECC chunk), which allows one to implement the ->eccpos() > and ->oobfree() functions with a simple logic that can be applied > to any size of OOB. Thanks for the work! This definitely needed done. I imagined that it might be best if we just changed the data structure format and have drivers allocate it dynamically during probe(), but actually, I kinda like generating it on the fly. The only concern I'd have is if there is significant penalty to doing this sort of computation on the fly during (e.g.) AUTO-layout OOB reads/writes. But I guess if there is such a penalty, nothing would stop us from caching the results in the MTD/NAND core code. > Patches 1 to 10 are just cleanups or trivial fixes that can be taken > independently. There were some comments for patch 1, and I want to look more closely at patch 10. But patches 2 to 9 are pushed to l2-mtd.git. Thanks! > Patch 19 is just an aggregate of several smaller commits (one per > driver), and has been submitted this way to limit the size of the > series. If everybody agrees on this approach, I'll resubmit the series > will those changes separated in different commits (as done here [1]). > > Also note that the last two commits are removing the nand_ecclayout > definition, thus preventing any new driver to use this structure. > Of course, this step can be delayed if some of the previous patches > are not accepted. I haven't looked in detail at the second half of the series, but I like the concept. I'll look closer once you fix up things in v2. Thanks, Brian > Best Regards, > > Boris > > [1]https://github.com/bbrezillon/linux-sunxi/commits/nand/ecclayout2
