[commit] r1933 - trunk

[repository service]

Author: stefanct
Date: Sat Feb 20 21:53:46 2016
New Revision: 1933
URL: http://flashrom.org/trac/flashrom/changeset/1933

Log:
dediprog: tremendously improve performance on SF600 by ignoring the spec.

The solution was discovered in a collaborative bug hunt with testing done by
David Hendricks. The actual culprit was found by Urja Rannikko by comparing
vanilla flashrom with David's version in chromiumos.

Signed-off-by: Stefan Tauner 
Tested-by: David Hendricks 
Acked-by: Stefan Tauner

Modified:
   trunk/dediprog.c

Modified: trunk/dediprog.c
==============================================================================
--- trunk/dediprog.c	Sat Feb 20 21:21:58 2016	(r1932)
+++ trunk/dediprog.c	Sat Feb 20 21:53:46 2016	(r1933)
@@ -694,6 +694,14 @@
    if (readcnt == 0) // If we don't require a response, we are done here
    	return 0;

+	/* The specifications do state the possibility to set a timeout for transceive transactions.
+	 * Apparently the "timeout" is a delay, and you can use long delays to accelerate writing - in case you
+	 * can predict the time needed by the previous command or so (untested). In any case, using this
+	 * "feature" to set sane-looking timouts for the read below will completely trash performance with
+	 * SF600 and/or firmwares >= 6.0 while they seem to be benign on SF100 with firmwares <= 5.5.2. *shrug*
+	 *
+	 * The specification also uses only 0 in its examples, so the lesson to learn here:
+	 * "Never trust the description of an interface in the documentation but use the example code and pray."
    const uint8_t read_timeout = 10 + readcnt/512;
    if (is_new_prot()) {
    	idx = 0;
@@ -703,6 +711,8 @@
    	value = min(read_timeout, 0xFF); // Possibly two bytes but we play safe here
    }
    ret = dediprog_read(CMD_TRANSCEIVE, value, idx, readarr, readcnt);
+	*/
+	ret = dediprog_read(CMD_TRANSCEIVE, 0, 0, readarr, readcnt);
    if (ret != readcnt) {
    	msg_perr("Receive SPI failed, expected %i, got %i %s!\n", readcnt, ret, libusb_error_name(ret));
    	return 1;