2 files changed, 33 insertions, 6 deletions

diff --git a/drivers/char/rtc.c b/drivers/char/rtc.c
index a162e1b3d5d3..0c66b802736a 100644
--- a/drivers/char/rtc.c
+++ b/drivers/char/rtc.c
@@ -918,12 +918,29 @@ static const struct file_operations rtc_proc_fops = {
 };
 #endif
 
+static resource_size_t rtc_size;
+
+static struct resource * __init rtc_request_region(resource_size_t size)
+{
+        struct resource *r;
+
+        if (RTC_IOMAPPED)
+                r = request_region(RTC_PORT(0), size, "rtc");
+        else
+                r = request_mem_region(RTC_PORT(0), size, "rtc");
+
+        if (r)
+                rtc_size = size;
+
+        return r;
+}
+
 static void rtc_release_region(void)
 {
         if (RTC_IOMAPPED)
-                release_region(RTC_PORT(0), RTC_IO_EXTENT);
+                release_region(RTC_PORT(0), rtc_size);
         else
-                release_mem_region(RTC_PORT(0), RTC_IO_EXTENT);
+                release_mem_region(RTC_PORT(0), rtc_size);
 }
 
 static int __init rtc_init(void)
@@ -976,10 +993,17 @@ found:
         }
 no_irq:
 #else
-        if (RTC_IOMAPPED)
-                r = request_region(RTC_PORT(0), RTC_IO_EXTENT, "rtc");
-        else
-                r = request_mem_region(RTC_PORT(0), RTC_IO_EXTENT, "rtc");
+        r = rtc_request_region(RTC_IO_EXTENT);
+
+        /*
+         * If we've already requested a smaller range (for example, because
+         * PNPBIOS or ACPI told us how the device is configured), the request
+         * above might fail because it's too big.
+         *
+         * If so, request just the range we actually use.
+         */
+        if (!r)
+                r = rtc_request_region(RTC_IO_EXTENT_USED);
         if (!r) {
 #ifdef RTC_IRQ
                 rtc_has_irq = 0;
diff --git a/include/linux/mc146818rtc.h b/include/linux/mc146818rtc.h
index 580b3f4956ee..2f4e957af656 100644
--- a/include/linux/mc146818rtc.h
+++ b/include/linux/mc146818rtc.h
@@ -109,8 +109,11 @@ struct cmos_rtc_board_info {
 #ifndef ARCH_RTC_LOCATION       /* Override by <asm/mc146818rtc.h>? */
 
 #define RTC_IO_EXTENT   0x8
+#define RTC_IO_EXTENT_USED      0x2
 #define RTC_IOMAPPED    1       /* Default to I/O mapping. */
 
+#else
+#define RTC_IO_EXTENT_USED      RTC_IO_EXTENT
 #endif /* ARCH_RTC_LOCATION */
 
 #endif /* _MC146818RTC_H */