tx4938ide: Check minimum cycle time and SHWT range (v2)

SHWT value is used as address valid to -CSx assertion and -CSx to -DIOx
assertion setup time, and contrarywise, -DIOx to -CSx release and -CSx
release to address invalid hold time, so it actualy applies 4 times and
so constitutes -DIOx recovery time.  Check requirement of the recovery
time and cycle time.  Also check SHWT maximum value.

Suggested-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Cc: ralf@linux-mips.org
Acked-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>

drivers/ide/tx4938ide.c

@@ -39,10 +39,17 @@ static void tx4938ide_tune_ebusc(unsigned int ebus_ch,
 	/* Address-valid to DIOR/DIOW setup */
 	shwt = DIV_ROUND_UP(t->setup, cycle);
 
+	/* -DIOx recovery time (SHWT * 4) and cycle time requirement */
+	while ((shwt * 4 + wt + (wt ? 2 : 3)) * cycle < t->cycle)
+		shwt++;
+	if (shwt > 7) {
+		pr_warning("tx4938ide: SHWT violation (%d)\n", shwt);
+		shwt = 7;
+	}
 	pr_debug("tx4938ide: ebus %d, bus cycle %dns, WT %d, SHWT %d\n",
 		 ebus_ch, cycle, wt, shwt);
 
-	__raw_writeq((cr & ~(0x3f007ull)) | (wt << 12) | shwt,
+	__raw_writeq((cr & ~0x3f007ull) | (wt << 12) | shwt,
 		     &tx4938_ebuscptr->cr[ebus_ch]);
 }