ACPI / nouveau: fix probing regression related to _DSM

Fix regression caused by commit b072e53, which breaks loading nouveau
driver on optimus laptops.

On some platforms, ACPI _DSM method (nouveau_op_dsm_muid, function 0)
has special requirements on the fourth parameter, which is different
from ACPI specifications. So revert to the private implementation
to check availability of _DSM functions instead of using common
acpi_check_dsm() interface.

Fixes: b072e53b0a27 (ACPI / nouveau: replace open-coded _DSM code with helper functions)
Reported-and-tested-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
[rjw: Subject]
Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/drivers/gpu/drm/nouveau/nouveau_acpi.c b/drivers/gpu/drm/nouveau/nouveau_acpi.c
index 4ef83df..83face3 100644 (file)
--- a/drivers/gpu/drm/nouveau/nouveau_acpi.c
+++ b/drivers/gpu/drm/nouveau/nouveau_acpi.c
@@ -106,6 +106,29 @@ static int nouveau_optimus_dsm(acpi_handle handle, int func, int arg, uint32_t *
        return 0;
 }
 
+/*
+ * On some platforms, _DSM(nouveau_op_dsm_muid, func0) has special
+ * requirements on the fourth parameter, so a private implementation
+ * instead of using acpi_check_dsm().
+ */
+static int nouveau_check_optimus_dsm(acpi_handle handle)
+{
+       int result;
+
+       /*
+        * Function 0 returns a Buffer containing available functions.
+        * The args parameter is ignored for function 0, so just put 0 in it
+        */
+       if (nouveau_optimus_dsm(handle, 0, 0, &result))
+               return 0;
+
+       /*
+        * ACPI Spec v4 9.14.1: if bit 0 is zero, no function is supported.
+        * If the n-th bit is enabled, function n is supported
+        */
+       return result & 1 && result & (1 << NOUVEAU_DSM_OPTIMUS_CAPS);
+}
+
 static int nouveau_dsm(acpi_handle handle, int func, int arg)
 {
        int ret = 0;
@@ -207,8 +230,7 @@ static int nouveau_dsm_pci_probe(struct pci_dev *pdev)
                           1 << NOUVEAU_DSM_POWER))
                retval |= NOUVEAU_DSM_HAS_MUX;
 
-       if (acpi_check_dsm(dhandle, nouveau_op_dsm_muid, 0x00000100,
-                          1 << NOUVEAU_DSM_OPTIMUS_CAPS))
+       if (nouveau_check_optimus_dsm(dhandle))
                retval |= NOUVEAU_DSM_HAS_OPT;
 
        if (retval & NOUVEAU_DSM_HAS_OPT) {