• Alex Smith's avatar
    mtd: nand: increase ready wait timeout and report timeouts · b70af9be
    Alex Smith authored
    If nand_wait_ready() times out, this is silently ignored, and its
    caller will then proceed to read from/write to the chip before it is
    ready. This can potentially result in corruption with no indication as
    to why.
    
    While a 20ms timeout seems like it should be plenty enough, certain
    behaviour can cause it to timeout much earlier than expected. The
    situation which prompted this change was that CPU 0, which is
    responsible for updating jiffies, was holding interrupts disabled
    for a fairly long time while writing to the console during a printk,
    causing several jiffies updates to be delayed. If CPU 1 happens to
    enter the timeout loop in nand_wait_ready() just before CPU 0 re-
    enables interrupts and updates jiffies, CPU 1 will immediately time
    out when the delayed jiffies updates are made. The result of this is
    that nand_wait_ready() actually waits less time than the NAND chip
    would normally take to be ready, and then read_page() proceeds to
    read out bad data from the chip.
    
    The situation described above may seem unlikely, but in fact it can be
    reproduced almost every boot on the MIPS Creator Ci20.
    
    Therefore, this patch increases the timeout to 400ms. This should be
    enough to cover cases where jiffies updates get delayed. In nand_wait()
    the timeout was previously chosen based on whether erasing or
    programming. This is changed to be 400ms unconditionally as well to
    avoid similar problems there. nand_wait() is also slightly refactored
    to be consistent with nand_wait{,_status}_ready(). These changes should
    have no effect during normal operation.
    
    Debugging this was made more difficult by the misleading comment above
    nand_wait_ready() stating "The timeout is caught later" - no timeout was
    ever reported, leading me away from the real source of the problem.
    Therefore, a pr_warn() is added when a timeout does occur so that it is
    easier to pinpoint similar problems in future.
    Signed-off-by: default avatarAlex Smith <alex.smith@imgtec.com>
    Signed-off-by: default avatarHarvey Hunt <harvey.hunt@imgtec.com>
    Reviewed-by: default avatarNiklas Cassel <niklas.cassel@axis.com>
    Cc: Alex Smith <alex@alex-smith.me.uk>
    Cc: Zubair Lutfullah Kakakhel <Zubair.Kakakhel@imgtec.com>
    Cc: David Woodhouse <dwmw2@infradead.org>
    Cc: Niklas Cassel <niklas.cassel@axis.com>
    Signed-off-by: default avatarBrian Norris <computersforpeace@gmail.com>
    b70af9be
nand_base.c 117 KB