ACPI/sbshc: Add 5us delay to fix SBS hang on MacBook

Commit Message

Chris Bainbridge May 18, 2015, 12:27 p.m. UTC

On Mon, May 18, 2015 at 10:20:33AM +0800, Brad Campbell wrote:
> On 30/04/15 04:21, Chris Bainbridge wrote:
> >
> >Supporting _OSI("Darwin") caused the MacBook firmware to expose the SBS,
> >resulting in intermittent hangs of several minutes on boot, and failure
> >to detect or report the battery. Fix this by adding a 5us delay to the
> >start of each SMBUS transaction. This timing is the result of
> >experimentation - hangs were observed with 3us but never with 5us.
> 
> G'day Chris,
> 
> Using 4.1-rc3 (whatever git head was from a couple of days ago) I've still
> been seeing ACPI lockups on my Macbook Pro (11,1). It appears to take a
> couple of suspend/resume cycles but seems to happen within 24 hours of
> booting whereas before this patch it was easy to hit.
> 
> As a test (and I do wonder if it'll lock up after I press send on this
> E-mail) I upped the delay to 10us and I've now been up for 1 day, 17:23 with
> the battery still responding to polling.
> 
> To make it easier to reproduce, I've been running a script that polls the
> battery every 60 seconds.
> 
> I figure I'll let it go for another couple of days, but I wanted to put this
> out there in case anyone else is seeing lockups after a longer period of
> uptime. The symptoms are the ACPI command just hangs as does 'cat
> /sys/class/power_supply/BAT0/status'. From there I can't suspend as the
> tasks can't be frozen and I just end up hard booting the machine.
> 
> I've removed Len & Rafael from the cc.
> 
> Regards,
> Brad

I used a patch similar to the following to test, it just runs the SBS
read in a loop. acpi_battery_get_info is run when the sbs module is
loaded. So start off with the 5us delay and a few runs through the loop
and verify you hit the hang, then increase the delay to 10us or whatever
and run the loop for a few thousand cycles until you're happy that
increasing the delay fixes the problem.


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Patch

diff --git a/drivers/acpi/sbs.c b/drivers/acpi/sbs.c
index 01504c8..74f8596 100644
--- a/drivers/acpi/sbs.c
+++ b/drivers/acpi/sbs.c
@@ -361,16 +361,21 @@  static int acpi_manager_get_info(struct acpi_sbs *sbs)
 static int acpi_battery_get_info(struct acpi_battery *battery)
 {
 	int i, result = 0;
-
-	for (i = 0; i < ARRAY_SIZE(info_readers); ++i) {
-		result = acpi_smbus_read(battery->sbs->hc,
-					 info_readers[i].mode,
-					 ACPI_SBS_BATTERY,
-					 info_readers[i].command,
-					 (u8 *) battery +
-						info_readers[i].offset);
-		if (result)
-			break;
+	int j;
+
+	for (j = 0; j < 1000; j++) {
+		for (i = 0; i < ARRAY_SIZE(info_readers); ++i) {
+			result = acpi_smbus_read(battery->sbs->hc,
+						 info_readers[i].mode,
+						 ACPI_SBS_BATTERY,
+						 info_readers[i].command,
+						 (u8 *) battery +
+							info_readers[i].offset);
+			if (result) {
+				printk("FAIL\n");
+				break;
+			}
+		}
 	}
 	return result;
 }