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

Commit 7bc5a2bad0b8 'ACPI: Support _OSI("Darwin") correctly' 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 5 us delay to the start of each
SMBUS transaction.  This timing is the result of experimentation -
hangs were observed with 3 us but never with 5 us.

Fixes: 7bc5a2bad0b8 'ACPI: Support _OSI("Darwin") correctly'
Link: https://bugzilla.kernel.org/show_bug.cgi?id=94651
Signed-off-by: Chris Bainbridge <chris.bainbridge@gmail.com>
Cc: 3.18+ <stable@vger.kernel.org> # 3.18+
[ rjw: Subject and changelog ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/drivers/acpi/sbshc.c b/drivers/acpi/sbshc.c
index 26e5b50605230e2e34a46d8118486fb1ba2eb939..bf034f8b7c1acde77f90ded7f39f70dbd636b7db 100644 (file)
--- a/drivers/acpi/sbshc.c
+++ b/drivers/acpi/sbshc.c
@@ -14,6 +14,7 @@
 #include <linux/delay.h>
 #include <linux/module.h>
 #include <linux/interrupt.h>
+#include <linux/dmi.h>
 #include "sbshc.h"
 
 #define PREFIX "ACPI: "
@@ -87,6 +88,8 @@ enum acpi_smb_offset {
        ACPI_SMB_ALARM_DATA = 0x26,     /* 2 bytes alarm data */
 };
 
+static bool macbook;
+
 static inline int smb_hc_read(struct acpi_smb_hc *hc, u8 address, u8 *data)
 {
        return ec_read(hc->offset + address, data);
@@ -132,6 +135,8 @@ static int acpi_smbus_transaction(struct acpi_smb_hc *hc, u8 protocol,
        }
 
        mutex_lock(&hc->lock);
+       if (macbook)
+               udelay(5);
        if (smb_hc_read(hc, ACPI_SMB_PROTOCOL, &temp))
                goto end;
        if (temp) {
@@ -257,12 +262,29 @@ extern int acpi_ec_add_query_handler(struct acpi_ec *ec, u8 query_bit,
                              acpi_handle handle, acpi_ec_query_func func,
                              void *data);
 
+static int macbook_dmi_match(const struct dmi_system_id *d)
+{
+       pr_debug("Detected MacBook, enabling workaround\n");
+       macbook = true;
+       return 0;
+}
+
+static struct dmi_system_id acpi_smbus_dmi_table[] = {
+       { macbook_dmi_match, "Apple MacBook", {
+         DMI_MATCH(DMI_BOARD_VENDOR, "Apple"),
+         DMI_MATCH(DMI_PRODUCT_NAME, "MacBook") },
+       },
+       { },
+};
+
 static int acpi_smbus_hc_add(struct acpi_device *device)
 {
        int status;
        unsigned long long val;
        struct acpi_smb_hc *hc;
 
+       dmi_check_system(acpi_smbus_dmi_table);
+
        if (!device)
                return -EINVAL;