On Tue, Dec 02, 2014 at 09:28:58AM +0100, Boris Brezillon wrote: > On Mon, 1 Dec 2014 15:37:48 -0800 Brian Norris <computersforpe...@gmail.com> > wrote: > > On Mon, Dec 01, 2014 at 09:18:18PM +0100, Boris Brezillon wrote: > > > On Mon, 1 Dec 2014 11:41:39 -0800 Brian Norris > > > <computersforpe...@gmail.com> wrote: > > > > On Mon, Dec 01, 2014 at 08:12:39PM +0100, Boris Brezillon wrote: > > > > > Brian, I really like the idea of having a generic implementation for > > > > > this > > > > > feature (using read_page_raw) as you suggested here [1], but this > > > > > implies > > > > > having a temporary buffer to store the page read in raw mode and keep > > > > > the page > > > > > read in normal (HW ECC engine eanbled) mode, and I'm not sure we want > > > > > to > > > > > allocate more buffers than we already have. > > > > > > > > Why does this require an additional buffer? If we've already noticed an > > > > ECC error, we're expected to return raw data anyway, so what's the > > > > problem with clobbering the original data with a raw version of the > > > > data? > > > > > > Well in the GPMI particular case (and more generally all NAND > > > controllers which do not support subpage write) this is true, but if you > > > can do subpage write, then you might have a bit flip in a specific > > > chunk which is still empty, while other chunks are written and are > > > expecting standard ECC correction. > > > In this case you want to keep the 3 chunks with standard ECC correction > > > and only one in raw mode with 'erased page bitflips' fixed. > > > > So the problem's not really with subpage write, exactly; the problem is > > for drivers that support subpage write, we don't have a way to perform a > > raw subpage read without touching the other subpages. > > Yes, that's what I was trying to explain :-), and the only solution I > see to address that is to have 2 buffers and then pick the most > appropriate data for a given chunk.
We actually sort of have two buffers already in nand_do_read_ops(); ops->databuf and chip->buffers->databuf. The former can be pretty small, but we could technically copy in any data that is "correct" to ops->databuf, and then clobber chip->buffers->databuf with raw data. But this may be more work than it's worth. > Do you think we should focus on support for "non subpage write" > controllers first, and then find an alternative for these controllers > if someone really needs it ? I think that may be alright. It doesn't look trivial to try to do an erased subpage check on the subpage-programmed case anyway, at least in generic code. We'd have to further understand what the OOB-per-subpage partitioning is, and that information isn't currently in our ecclayout. Brian -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
