ahci: correct ncq sector count

uint16_t isn't enough to hold the real sector count, since a value of
zero implies a full 64K sectors, so we need a uint32_t here.

We *could* cheat and pretend that this value is 0-based and fit it in
a uint16_t, but I'd rather waste 2 bytes instead of a future dev's
10 minutes when they forget to +1/-1 accordingly somewhere.

See SATA 3.2, section 13.6.4.1 "READ FPDMA QUEUED".

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 1435767578-32743-9-git-send-email-jsnow@redhat.com

hw/ide/ahci.c

@@ -1086,8 +1086,11 @@ static void process_ncq_command(AHCIState *s, int port, uint8_t *cmd_fis,
         DPRINTF(port, "Warn: Unsupported attempt to use Rebuild Assist\n");
     }
 
-    ncq_tfs->sector_count = ((uint16_t)ncq_fis->sector_count_high << 8) |
-                                ncq_fis->sector_count_low;
+    ncq_tfs->sector_count = ((ncq_fis->sector_count_high << 8) |
+                             ncq_fis->sector_count_low);
+    if (!ncq_tfs->sector_count) {
+        ncq_tfs->sector_count = 0x10000;
+    }
     size = ncq_tfs->sector_count * 512;
     ahci_populate_sglist(ad, &ncq_tfs->sglist, size, 0);
 

hw/ide/ahci.h

@@ -256,7 +256,7 @@ typedef struct NCQTransferState {
     BlockAIOCB *aiocb;
     QEMUSGList sglist;
     BlockAcctCookie acct;
-    uint16_t sector_count;
+    uint32_t sector_count;
     uint64_t lba;
     uint8_t tag;
     uint8_t cmd;