• Arnd Bergmann's avatar
    mtd: avoid stack overflow in MTD CFI code · fddcca51
    Arnd Bergmann authored
    
    
    When map_word gets too large, we use a lot of kernel stack, and for
    MTD_MAP_BANK_WIDTH_32, this means we use more than the recommended
    1024 bytes in a number of functions:
    
    drivers/mtd/chips/cfi_cmdset_0020.c: In function 'cfi_staa_write_buffers':
    drivers/mtd/chips/cfi_cmdset_0020.c:651:1: warning: the frame size of 1336 bytes is larger than 1024 bytes [-Wframe-larger-than=]
    drivers/mtd/chips/cfi_cmdset_0020.c: In function 'cfi_staa_erase_varsize':
    drivers/mtd/chips/cfi_cmdset_0020.c:972:1: warning: the frame size of 1208 bytes is larger than 1024 bytes [-Wframe-larger-than=]
    drivers/mtd/chips/cfi_cmdset_0001.c: In function 'do_write_buffer':
    drivers/mtd/chips/cfi_cmdset_0001.c:1835:1: warning: the frame size of 1240 bytes is larger than 1024 bytes [-Wframe-larger-than=]
    
    This can be avoided if all operations on the map word are done
    indirectly and the stack gets reused between the calls. We can
    mostly achieve this by selecting MTD_COMPLEX_MAPPINGS whenever
    MTD_MAP_BANK_WIDTH_32 is set, but for the case that no other
    bank width is enabled, we also need to use a non-constant
    map_bankwidth() to convince the compiler to use less stack.
    
    Signed-off-by: default avatarArnd Bergmann <arnd@arndb.de>
    [Brian: this patch mostly achieves its goal by forcing
        MTD_COMPLEX_MAPPINGS (and the accompanying indirection) for 256-bit
        mappings; the rest of the change is mostly a wash, though it helps
        reduce stack size slightly. If we really care about supporting
        256-bit mappings though, we should consider rewriting some of this
        code to avoid keeping and assigning so many 256-bit objects on the
        stack.]
    Signed-off-by: default avatarBrian Norris <computersforpeace@gmail.com>
    fddcca51