ALSA: AACI: allow writes to MAINCR to take effect

The AACI TRM requires the MAINCR enable bit to be held zero for two
bitclk cycles plus three apb_pclk cycles.  Use a delay of 1us to
ensure this.

Ensure that writes to MAINCR to change the addressed codec only happen
when required, and that they take effect in a similar manner to the
above, otherwise we seem to occasionally have stuck slot busy bits.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

sound/arm/aaci.c

@@ -50,7 +50,11 @@ static void aaci_ac97_select_codec(struct aaci *aaci, struct snd_ac97 *ac97)
 	if (v & SLFR_1RXV)
 		readl(aaci->base + AACI_SL1RX);
 
-	writel(maincr, aaci->base + AACI_MAINCR);
+	if (maincr != readl(aaci->base + AACI_MAINCR)) {
+		writel(maincr, aaci->base + AACI_MAINCR);
+		readl(aaci->base + AACI_MAINCR);
+		udelay(1);
+	}
 }
 
 /*
@@ -993,6 +997,8 @@ static unsigned int __devinit aaci_size_fifo(struct aaci *aaci)
 	 * disabling the channel doesn't clear the FIFO.
 	 */
 	writel(aaci->maincr & ~MAINCR_IE, aaci->base + AACI_MAINCR);
+	readl(aaci->base + AACI_MAINCR);
+	udelay(1);
 	writel(aaci->maincr, aaci->base + AACI_MAINCR);
 
 	/*