acpi/nfit: Require opt-in for read-only label configurations

Recent fixes to command handling enabled Linux to read label
configurations that it could not before. Unfortunately that means that
configurations that were operating in label-less mode will be broken as
the kernel ignores the existing namespace configuration and tries to
honor the new found labels.

Fortunately this seems limited to a case where Linux can quirk the
behavior and maintain the existing label-less semantics by default.
When the platform does not emit an _LSW method, disable all label access
methods. Provide a 'force_labels' module parameter to allow read-only
label operation.

Fixes: 11189c1089da ("acpi/nfit: Fix command-supported detection")
Reported-by: Dexuan Cui <decui@microsoft.com>
Reviewed-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

diff --git a/drivers/acpi/nfit/core.c b/drivers/acpi/nfit/core.c
index 811c399a3a7653aed1672d976427aab4dd229653..5b5e802de7b84990b7481f1a0cb6c3cb8845d52f 100644 (file)
--- a/drivers/acpi/nfit/core.c
+++ b/drivers/acpi/nfit/core.c
@@ -56,6 +56,10 @@ static bool no_init_ars;
 module_param(no_init_ars, bool, 0644);
 MODULE_PARM_DESC(no_init_ars, "Skip ARS run at nfit init time");
 
+static bool force_labels;
+module_param(force_labels, bool, 0444);
+MODULE_PARM_DESC(force_labels, "Opt-in to labels despite missing methods");
+
 LIST_HEAD(acpi_descs);
 DEFINE_MUTEX(acpi_desc_lock);
 
@@ -1916,6 +1920,19 @@ static int acpi_nfit_add_dimm(struct acpi_nfit_desc *acpi_desc,
                        dev_dbg(dev, "%s: has _LSW\n", dev_name(&adev_dimm->dev));
                        set_bit(NFIT_MEM_LSW, &nfit_mem->flags);
                }
+
+               /*
+                * Quirk read-only label configurations to preserve
+                * access to label-less namespaces by default.
+                */
+               if (!test_bit(NFIT_MEM_LSW, &nfit_mem->flags)
+                               && !force_labels) {
+                       dev_dbg(dev, "%s: No _LSW, disable labels\n",
+                                       dev_name(&adev_dimm->dev));
+                       clear_bit(NFIT_MEM_LSR, &nfit_mem->flags);
+               } else
+                       dev_dbg(dev, "%s: Force enable labels\n",
+                                       dev_name(&adev_dimm->dev));
        }
 
        populate_shutdown_status(nfit_mem);