[PATCH] ACPI: bus: Avoid misleading _OSC missing-feature errors

[Saverio Miroddi <saverio.pub2@gmail.com>]

The ACPI specification defines OSC_CAPABILITIES_MASK_ERROR to mean that
firmware cleared capability bits requested by the operating system. Some
firmware sets this status during the control request while returning every
requested capability unchanged. On the affected system, the requested and
returned masks were both 0x006a7eff.

Commit e5322888e6bf ("ACPI: bus: Rework the handling of \_SB._OSC
platform features") made all control-response errors produce error-level
messages. Consequently, the inconsistent response above now claims that
features may be missing even though none were removed.

Track whether the response actually clears a requested bit and omit the
error-level messages only if OSC_CAPABILITIES_MASK_ERROR is the sole
error and no capability was cleared. Keep the dynamic-debug diagnostic and
leave the negotiated capability mask and all other error cases unchanged.

Fixes: e5322888e6bf ("ACPI: bus: Rework the handling of \_SB._OSC platform features")
Signed-off-by: Saverio Miroddi <saverio.pub2@gmail.com>
---
 drivers/acpi/bus.c | 23 ++++++++++++++++-------
 1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
index a30a904f6535..c13128cbc2f6 100644
--- a/drivers/acpi/bus.c
+++ b/drivers/acpi/bus.c
@@ -335,7 +335,8 @@ static int acpi_osc_handshake(acpi_handle handle, const char *uuid_str,
 		.length = bufsize * sizeof(u32),
 	};
 	struct acpi_buffer output;
-	u32 *retbuf, test;
+	u32 *retbuf, test, errors;
+	bool capabilities_masked = false;
 	guid_t guid;
 	int ret, i;
 
@@ -395,16 +396,24 @@ static int acpi_osc_handshake(acpi_handle handle, const char *uuid_str,
 	 * Clear the feature bits in capbuf[] that have not been acknowledged.
 	 * After that, capbuf[] contains the resultant feature mask.
 	 */
-	for (i = OSC_QUERY_DWORD + 1; i < bufsize; i++)
+	for (i = OSC_QUERY_DWORD + 1; i < bufsize; i++) {
+		if (capbuf[i] & ~retbuf[i])
+			capabilities_masked = true;
+
 		capbuf[i] &= retbuf[i];
+	}
 
-	if (retbuf[OSC_QUERY_DWORD] & OSC_ERROR_MASK) {
+	errors = retbuf[OSC_QUERY_DWORD] & OSC_ERROR_MASK;
+	if (errors) {
 		/*
-		 * Complain about the unexpected errors and print diagnostic
-		 * information related to them.
+		 * Some firmware sets OSC_CAPABILITIES_MASK_ERROR without clearing
+		 * any requested capability.  Only complain if another error is
+		 * present or a capability was actually masked.
 		 */
-		acpi_handle_err(handle, "_OSC: errors while processing control request\n");
-		acpi_handle_err(handle, "_OSC: some features may be missing\n");
+		if (errors != OSC_CAPABILITIES_MASK_ERROR || capabilities_masked) {
+			acpi_handle_err(handle, "_OSC: errors while processing control request\n");
+			acpi_handle_err(handle, "_OSC: some features may be missing\n");
+		}
 		acpi_osc_error_check(handle, &guid, rev, &cap, retbuf);
 	}
 
-- 
2.54.0