rtc: cmos: Do not assume irq 8 for rtc when there are no legacy irqs

On some systems (e.g. Intel Bay Trail systems) the legacy PIC is not
used, in this case virq 8 will be a random irq, rather then hw_irq 8
from the PIC.

Requesting virq 8 in this case will not help us to get alarm irqs and
may cause problems for other drivers which actually do need virq 8,
for example on an Asus Transformer T100TA this leads to:

[ 28.745155] genirq: Flags mismatch irq 8. 00000088 (mmc0) vs. 00000080 (rtc0)
<snip oops>
[ 28.753700] mmc0: Failed to request IRQ 8: -16
[ 28.975934] sdhci-acpi: probe of 80860F14:01 failed with error -16

This commit fixes this by making the rtc-cmos driver continue
without using an irq rather then claiming irq 8 when no irq is
specified in the pnp-info and there are no legacy-irqs.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

drivers/rtc/rtc-cmos.c

@@ -41,6 +41,9 @@
 #include <linux/pm.h>
 #include <linux/of.h>
 #include <linux/of_platform.h>
+#ifdef CONFIG_X86
+#include <asm/i8259.h>
+#endif
 
 /* this is for "generic access to PC-style RTC" using CMOS_READ/CMOS_WRITE */
 #include <linux/mc146818rtc.h>
@@ -1193,17 +1196,23 @@ static int cmos_pnp_probe(struct pnp_dev *pnp, const struct pnp_device_id *id)
 {
 	cmos_wake_setup(&pnp->dev);
 
-	if (pnp_port_start(pnp, 0) == 0x70 && !pnp_irq_valid(pnp, 0))
+	if (pnp_port_start(pnp, 0) == 0x70 && !pnp_irq_valid(pnp, 0)) {
+		unsigned int irq = 0;
+#ifdef CONFIG_X86
 		/* Some machines contain a PNP entry for the RTC, but
 		 * don't define the IRQ. It should always be safe to
-		 * hardcode it in these cases
+		 * hardcode it on systems with a legacy PIC.
 		 */
+		if (nr_legacy_irqs())
+			irq = 8;
+#endif
 		return cmos_do_probe(&pnp->dev,
-				pnp_get_resource(pnp, IORESOURCE_IO, 0), 8);
-	else
+				pnp_get_resource(pnp, IORESOURCE_IO, 0), irq);
+	} else {
 		return cmos_do_probe(&pnp->dev,
 				pnp_get_resource(pnp, IORESOURCE_IO, 0),
 				pnp_irq(pnp, 0));
+	}
 }
 
 static void cmos_pnp_remove(struct pnp_dev *pnp)