Not for merge... yet.
It works for dummy, nothing else was tested.
Limitations/bugs mentioned in the patch.

Signed-off-by: Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006@gmx.net>

Index: flashrom-spi_cache_rdid/spi.c
===================================================================
--- flashrom-spi_cache_rdid/spi.c       (Revision 1611)
+++ flashrom-spi_cache_rdid/spi.c       (Arbeitskopie)
@@ -24,18 +24,46 @@

 #include <strings.h>
 #include <string.h>
+#include <stdlib.h>
 #include "flash.h"
 #include "flashchips.h"
 #include "chipdrivers.h"
 #include "programmer.h"
 #include "spi.h"

+/* FIXME: We want a per-command cache, not just a RDID cache.
+ * FIXME: We should cache this for spi_send_multicommand programmers as well.
+ */
+struct rdidcache {
+       int available;
+       unsigned char *readarr;
+} rdidcache = {0};
+
 int spi_send_command(struct flashctx *flash, unsigned int writecnt,
                     unsigned int readcnt, const unsigned char *writearr,
                     unsigned char *readarr)
 {
-       return flash->pgm->spi.command(flash, writecnt, readcnt, writearr,
+       int ret;
+       unsigned char *tmp;
+
+       if ((writearr[0] == JEDEC_RDID) && (rdidcache.available >= readcnt)) {
+               memcpy(readarr, rdidcache.readarr, readcnt);
+               return 0;
+       }
+       ret = flash->pgm->spi.command(flash, writecnt, readcnt, writearr,
                                       readarr);
+       if (!ret && (writearr[0] == JEDEC_RDID) && (rdidcache.available < readcnt)) {
+               tmp = realloc(rdidcache.readarr, readcnt);
+               if (!tmp) {
+                       /* Oh well. Don't cache stuff, then. No problem. */
+                       msg_perr("Doom due to OOM! Brace for impact!\n");
+                       return ret;
+               }
+               rdidcache.readarr = tmp;
+               rdidcache.available = readcnt;
+               memcpy(rdidcache.readarr, readarr, readcnt);
+       }
+       return ret;
 }

 int spi_send_multicommand(struct flashctx *flash, struct spi_command *cmds)