[PATCH v2] mtd: nand: ecc-hamming: Clarify the logic around rp17

[Miquel Raynal]

This code has been written in 2008 and is fine, but in order to keep
robots happy, I think it's time to change a little bit this code just
to clarify the different possible values of eccsize_mult. Indeed, this
variable may only take the value 1 or 2 because step_size, in the case
of the software Hamming ECC engine may only be 256 or 512. Depending
on the value of eccsize_mult, an extra rp17 variable is set, or not
and triggers the following warning:

     smatch warnings:
     ecc_sw_hamming_calculate() error: uninitialized symbol 'rp17'.

As highlighted by Dan Carpenter, if the only possible values for
eccsize_mult are 1 and 2, then the code is fine, but "it's hard to
tell just from looking".

So instead of shifting step_size, let's use a ternary condition to
assign to eccsize_mult the only two possible values and clarify the
driver's logic.

Now that the situation is clarified for humans, ensure rp17 is
initialized to 0 to keep compilers and robots silent as well.

Reported-by: kernel test robot <lkp at intel.com>
Reported-by: Dan Carpenter <dan.carpenter at oracle.com>
Signed-off-by: Miquel Raynal <miquel.raynal at bootlin.com>
---
 drivers/mtd/nand/ecc-sw-hamming.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/mtd/nand/ecc-sw-hamming.c b/drivers/mtd/nand/ecc-sw-hamming.c
index 334e619b35c9..77e6005a22b0 100644
--- a/drivers/mtd/nand/ecc-sw-hamming.c
+++ b/drivers/mtd/nand/ecc-sw-hamming.c
@@ -116,7 +116,7 @@ int ecc_sw_hamming_calculate(const unsigned char *buf, unsigned int step_size,
 			     unsigned char *code, bool sm_order)
 {
 	const u32 *bp = (uint32_t *)buf;
-	const u32 eccsize_mult = step_size >> 8;
+	const u32 eccsize_mult = (step_size == 256) ? 1 : 2;
 	/* current value in buffer */
 	u32 cur;
 	/* rp0..rp17 are the various accumulated parities (per byte) */
@@ -136,6 +136,7 @@ int ecc_sw_hamming_calculate(const unsigned char *buf, unsigned int step_size,
 	rp12 = 0;
 	rp14 = 0;
 	rp16 = 0;
+	rp17 = 0;
 
 	/*
 	 * The loop is unrolled a number of times;
-- 
2.20.1