[PATCH] mtd: rawnand: fsmc: Change to non-atomic bit operations

[Fenghua Yu <fenghua.yu@xxxxxxxxx>]

No need to use expensive atomic change_bit() on dat[] and err_idx[]:
1. fsmc_bch8_correct_data() is called while mutex chip->lock is held
2. err_idx[] is a local variable.

To avoid big endian concern due to type cast to unsigned long, directly
change the bit in the specified byte instead of using non-atomic
__change_bit().

Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>
---

This driver only works on ARM. We find unaligned access in change_bit()
is quite expensive on x86. Although this driver is not configured
and compiled on x86, I send this patch to you in case it's useful.
I haven't compiled or tested this patch yet.

 drivers/mtd/nand/raw/fsmc_nand.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/mtd/nand/raw/fsmc_nand.c b/drivers/mtd/nand/raw/fsmc_nand.c
index a6964feeec77..7e28311dffcb 100644
--- a/drivers/mtd/nand/raw/fsmc_nand.c
+++ b/drivers/mtd/nand/raw/fsmc_nand.c
@@ -809,11 +809,12 @@ static int fsmc_bch8_correct_data(struct nand_chip *chip, u8 *dat,
 
 	i = 0;
 	while (num_err--) {
-		change_bit(0, (unsigned long *)&err_idx[i]);
-		change_bit(1, (unsigned long *)&err_idx[i]);
+		err_idx[i] ^= 3;
 
 		if (err_idx[i] < chip->ecc.size * 8) {
-			change_bit(err_idx[i], (unsigned long *)dat);
+			int err = err_idx[i];
+
+			dat[err >> 3] ^= BIT(err & 7);
 			i++;
 		}
 	}
-- 
2.19.1


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