tpm: read burstcount from TPM_STS in one 32-bit transaction

commit 9754d45e upstream.

Some chips incorrectly support partial reads from TPM_STS register
at non-zero offsets. Read the entire 32-bits register instead of
making two 8-bit reads to support such devices and reduce the number
of bus transactions when obtaining the burstcount from TPM_STS.

Fixes: 27084efe ("tpm: driver for next generation TPM chips")
Signed-off-by: Andrey Pronin <apronin@chromium.org>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
[bwh: Backported to 3.16:
 - Use raw ioread32() instead of tpm_tis_read32()
 - Adjust filename, context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/char/tpm/tpm_tis.c

@@ -197,16 +197,15 @@ static int get_burstcount(struct tpm_chip *chip)
 {
 	unsigned long stop;
 	int burstcnt;
+	u32 value;
 
 	/* wait for burstcount */
 	/* which timeout value, spec has 2 answers (c & d) */
 	stop = jiffies + chip->vendor.timeout_d;
 	do {
-		burstcnt = ioread8(chip->vendor.iobase +
-				   TPM_STS(chip->vendor.locality) + 1);
-		burstcnt += ioread8(chip->vendor.iobase +
-				    TPM_STS(chip->vendor.locality) +
-				    2) << 8;
+		value = ioread32(chip->vendor.iobase +
+				 TPM_STS(chip->vendor.locality));
+		burstcnt = (value >> 8) & 0xFFFF;
 		if (burstcnt)
 			return burstcnt;
 		msleep(TPM_TIMEOUT);