Hello, This series aims at adding a power-cut emulation layer at the nandsim level. The final goal is to support MLC NAND emulation in nandsim in order to validate the work done in the NAND, UBI and UBIFS layers to reliably support those chips.
Even though the UBI layer already provides a power-cut emulation infrastructure, I decided to add one at the nandsim layer for the following reasons: - IMO it is cleaner to isolate MLC NAND emulation in the NAND layer - emulating unstable bits in UBI is not so easy: the unstable bits issue happens when a program or erase operation is interrupted (by a power-cut) while it is almost finished. In this case the next read operation will succeed (return the expected data), but not the following ones. Emulating this problem requires knowing which block/page was being accessed when the power-cut occurred, and if we want to validate that UBI (not UBIFS) is robust to such errors, we have to reattach the mtd partition to the UBI layer, and by doing that we loose the information of which page/block was being programmed/erased when the power-cut occurred. By implementing the power-cut emulation at the nandsim level, we can easily detach/attach the emulated device, and check still keep those information. - emulating paired pages in UBI is a bit easier but still requires some knowledge about the pairing scheme (which differs from one chip to another), and I'm not sure yet how this will be exposed by the MTD/NAND layers. This being said, I might be wrong in my assumptions, so feel free to comment on that decision. Regarding the code itself, this series adds a simple power-cut emulation layer, and modifies the intermediate layers (NAND and UBI) to forward emulated power-cut errors and let the UBIFS layer switch into read-only mode. Paired pages and unstable bits emulation is not part of the series, but can be added on top of those changes by tweaking the actions taken in nandsim when a power-cut is emulated. Also, I'm not sure about the method used to inform NAND core when a power-cut was emulated: I'm currently adding a virtual NAND status flag, but adding a new field in the nand_chip struct might be a better approach. This would also allow us to compile out code sections that are only useful when doing NAND emulation. Best Regards, Boris Boris Brezillon (5): mtd: nand: add basic stuff to support power-cut emulation mtd: nand: return -EROFS in case of power-cut emulation UBI: switch the UBI device in read-only mode when mtd returns -EROFS mtd: nand: nandsim: implement ->get_status() mtd: nand: nandsim: add support for power-cut emulation drivers/mtd/nand/nand_base.c | 34 ++++++-- drivers/mtd/nand/nandsim.c | 182 ++++++++++++++++++++++++++++++++++++++++--- drivers/mtd/ubi/io.c | 4 +- include/linux/mtd/nand.h | 4 + 4 files changed, 207 insertions(+), 17 deletions(-) -- 1.9.1 -- 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/