From: Wolfgang Denk wd@xpert.denx.de
This patch fixes a problem on systems where the NOR flash is attached to a 64 bit bus. The toggle bit detection in flash_toggle() is based on the assumption that the same flash address is read twice without any other interjacent flash accesses. However, on 32 bit systems the function flash_read64() [as currently implemented] does not perform an atomic 64 bit read - instead, this is broken down into two 32 bit read accesses on addresses "addr" and "addr + 4". So instead of reading a 64 bit value twice from "addr", we see a sequence of 4 32 bit reads from "addr", "addr + 4", "addr", and "addr + 4". The consequence is that flash_toggle() fails to work.
This patch implements a simple, but somewhat ugly solution, as it avoids the use of flash_read64() in this critical place (by breaking it down manually into 32 bit read operations) instead of rewriting flash_read64() such to perform atomic 64 bit reads as one could expect. However, such a rewrite would require the use of floating point load operations, which becomes pretty complex:
save MSR; set Floating Point Enable bit in MSR; use "lfd" instruction to perform atomic 64 bit read; use "stfd" to store value to temporary variable on stack; load u64 value from temporary variable; restore saved MSR; return u64 value;
The benefit-cost ratio of such an implementation was considered too bad to actually attempt this, especially as we can expect that such an implementation would not only have a bigger memory footprint but also cause a performance degradation.
Signed-off-by: Wolfgang Denk wd@denx.de --- drivers/mtd/cfi_flash.c | 3 ++- 1 files changed, 2 insertions(+), 1 deletions(-)
diff --git a/drivers/mtd/cfi_flash.c b/drivers/mtd/cfi_flash.c index c40bf66..24e9b9f 100644 --- a/drivers/mtd/cfi_flash.c +++ b/drivers/mtd/cfi_flash.c @@ -596,7 +596,8 @@ static int flash_toggle (flash_info_t * info, flash_sect_t sect, retval = flash_read32(addr) != flash_read32(addr); break; case FLASH_CFI_64BIT: - retval = flash_read64(addr) != flash_read64(addr); + retval = ( (flash_read32( addr ) != flash_read32( addr )) || + (flash_read32(addr+4) != flash_read32(addr+4)) ); break; default: retval = 0;