From patchwork Fri Feb 12 15:39:29 2010
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Subject: Avoid SPI RES if REMS is available
Date: Fri, 12 Feb 2010 15:39:29 -0000
From: Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006@gmx.net>
X-Patchwork-Id: 917
Message-Id: <4B757631.2030105@gmx.net>
To: flashrom <flashrom@flashrom.org>

SPI RES is the most unreliable way to identify chips because it only
returns a 1-byte ID for most chips. For every given ID out there,
probably a dozen incompatible flash chips match it.
We already refuse to identify a chip with RES if that chip responds to
RDID (3 bytes, good match), and with this patch we additionally refuse
RES if the chip responds to REMS (2 bytes, still a good match). This
increases matching accuracy a lot.

Besides that, the RDID/REMS response checking has been cleaned up for
better readability.

Signed-off-by: Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006@gmx.net>
Acked-by: Sean Nelson <audiohacked@gmail.com>


Index: flashrom-spi_res_avoidance/spi.c
===================================================================
--- flashrom-spi_res_avoidance/spi.c	(Revision 896)
+++ flashrom-spi_res_avoidance/spi.c	(Arbeitskopie)
@@ -385,17 +385,30 @@
 {
 	unsigned char readarr[3];
 	uint32_t id2;
+	const unsigned char allff[] = {0xff, 0xff, 0xff};
+	const unsigned char all00[] = {0x00, 0x00, 0x00};
 
-	/* Check if RDID was successful and did not return 0xff 0xff 0xff.
-	 * In that case, RES is pointless.
+	/* Check if RDID is usable and does not return 0xff 0xff 0xff or
+	 * 0x00 0x00 0x00. In that case, RES is pointless.
 	 */
-	if (!spi_rdid(readarr, 3) && ((readarr[0] != 0xff) ||
-	    (readarr[1] != 0xff) || (readarr[2] != 0xff)))
+	if (!spi_rdid(readarr, 3) && memcmp(readarr, allff, 3) &&
+	    memcmp(readarr, all00, 3)) {
+		msg_cdbg("Ignoring RES in favour of RDID.\n");
 		return 0;
+	}
+	/* Check if REMS is usable and does not return 0xff 0xff or
+	 * 0x00 0x00. In that case, RES is pointless.
+	 */
+	if (!spi_rems(readarr) && memcmp(readarr, allff, JEDEC_REMS_INSIZE) &&
+	    memcmp(readarr, all00, JEDEC_REMS_INSIZE)) {
+		msg_cdbg("Ignoring RES in favour of REMS.\n");
+		return 0;
+	}
 
 	if (spi_res(readarr))
 		return 0;
 
+	/* FIXME: Handle the case where RES gives a 2-byte response. */
 	id2 = readarr[0];
 	printf_debug("%s: id 0x%x\n", __func__, id2);
 	if (id2 != flash->model_id)