Honor ICH SPI address window for reads

ICH SPI has the ability to restrict SPI read/write accesses to a given
address range. The low end of the range is configurable by the BIOS (and
by flashrom if the BIOS didn't lock down the flash interface), the high
end of the range is 0xffffff (2^24-1).
This patch checks for an address range restriction and uses the low end
of the allowed range as base for SPI reads. A similar workaround for
REMS/RES opcodes has been committed in r500.

This fixes read on the Intel D945GCLF mainboard where the stock BIOS
enforces a restricted address range.
Please note that writes need the same fix, but for architectural reasons
that fix will be merged once partial write is available.

Corresponding to flashrom svn r1170.
Signed-off-by: Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006@gmx.net>

Tested by David Hendricks on the Intel D945GCLF mainboard, results at
http://paste.flashrom.org/view.php?id=79

Acked-by: David Hendricks <dhendrix@google.com>

spi.c

@@ -22,6 +22,7 @@
  * Contains the generic SPI framework
  */
 
+#include <string.h>
 #include "flash.h"
 #include "flashchips.h"
 #include "chipdrivers.h"
@@ -207,6 +208,7 @@ int default_spi_send_multicommand(struct spi_command *cmds)
 
 int spi_chip_read(struct flashchip *flash, uint8_t *buf, int start, int len)
 {
+	int addrbase = 0;
 	if (!spi_programmer[spi_controller].read) {
 		msg_perr("%s called, but SPI read is unsupported on this "
 			 "hardware. Please report a bug at "
@@ -214,7 +216,26 @@ int spi_chip_read(struct flashchip *flash, uint8_t *buf, int start, int len)
 		return 1;
 	}
 
-	return spi_programmer[spi_controller].read(flash, buf, start, len);
+	/* Check if the chip fits between lowest valid and highest possible
+	 * address. Highest possible address with the current SPI implementation
+	 * means 0xffffff, the highest unsigned 24bit number.
+	 */
+	addrbase = spi_get_valid_read_addr();
+	if (addrbase + flash->total_size * 1024 > (1 << 24)) {
+		msg_perr("Flash chip size exceeds the allowed access window. ");
+		msg_perr("Read will probably fail.\n");
+		/* Try to get the best alignment subject to constraints. */
+		addrbase = (1 << 24) - flash->total_size * 1024;
+	}
+	/* Check if alignment is native (at least the largest power of two which
+	 * is a factor of the mapped size of the chip).
+	 */
+	if (ffs(flash->total_size * 1024) > (ffs(addrbase) ? : 33)) {
+		msg_perr("Flash chip is not aligned natively in the allowed "
+			 "access window.\n");
+		msg_perr("Read will probably return garbage.\n");
+	}
+	return spi_programmer[spi_controller].read(flash, buf, addrbase + start, len);
 }
 
 /*