RE: [PATCH 4/6] ACPI: Execute platform _OSC also with query bit clear

On Tue, Jan 26, 2021 at 5:01 PM Mika Westerberg
[off-list ref] wrote:

quoted

From: Mario Limonciello <redacted>

The platform _OSC can change the hardware state when query bit is not
set. According to ACPI spec it is recommended that the OS runs _OSC with
query bit set until the platform does not mask any of the capabilities.
Then it should run it with query bit clear in order to actually commit
the changes. At the moment Linux only runs the _OSC with query bit set

And that's because there was nothing it could ask to control using the
_SB scope _OSC.

Today it is just reporting what features are supported by it.

However, with the upcoming USB4 CM support it needs to ask for the
control of that feature and that's why the _SB scope _OSC support
needs to be extended.  So it is not a fix for a bug or missing spec
coverage, which this part of the changelog kind of implies, it's just
enabling a new feature.

Other operating systems behave as described in the ACPI spec long before USB4 CM
support was added.  Admittedly this is semantics of whether to call it
a "bug", but specifically the lack of this in the existing Linux kernel code
*can* actually cause you to get into a situation where you have no functional
USB4.  This will happen if you boot between two different kernels or potentially
two different operating systems.  This is due to how the selection of FW or SW
CM is made.  If this patch "alone" was brought further backward the older kernels
FW CM mode would be activated in those situations.

quoted

and this is going to cause problems with the USB4 CM (Connection
Manager) switch that is going to commit the switch only when the OS
requests control over the feature.

For this reason modify the _OSC support so that we first execute it with
query bit set, then use the returned valu as base of the features we

s/valu/value/

quoted

want to control and run the _OSC again with query bit clear.

Also rename the function to better match what it does.

Cc: Rafael J. Wysocki <redacted>
Signed-off-by: Mario Limonciello <redacted>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

---
 drivers/acpi/bus.c | 43 +++++++++++++++++++++++++++++++------------
 1 file changed, 31 insertions(+), 12 deletions(-)

diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
index 1682f8b454a2..ca7c7b2bf56e 100644
--- a/drivers/acpi/bus.c
+++ b/drivers/acpi/bus.c

@@ -282,9 +282,9 @@ bool osc_pc_lpi_support_confirmed;
 EXPORT_SYMBOL_GPL(osc_pc_lpi_support_confirmed);

 static u8 sb_uuid_str[] = "0811B06E-4A27-44F9-8D60-3CBBC22E7B48";
-static void acpi_bus_osc_support(void)
+static void acpi_bus_osc_negotiate_platform_control(void)
 {
-       u32 capbuf[2];
+       u32 capbuf[2], *capbuf_ret;
        struct acpi_osc_context context = {
                .uuid_str = sb_uuid_str,
                .rev = 1,

@@ -321,17 +321,36 @@ static void acpi_bus_osc_support(void)
                capbuf[OSC_SUPPORT_DWORD] |= OSC_SB_APEI_SUPPORT;
        if (ACPI_FAILURE(acpi_get_handle(NULL, "\\_SB", &handle)))
                return;
-       if (ACPI_SUCCESS(acpi_run_osc(handle, &context))) {
-               u32 *capbuf_ret = context.ret.pointer;
-               if (context.ret.length > OSC_SUPPORT_DWORD) {
-                       osc_sb_apei_support_acked =
-                               capbuf_ret[OSC_SUPPORT_DWORD] &

OSC_SB_APEI_SUPPORT;

quoted

-                       osc_pc_lpi_support_confirmed =
-                               capbuf_ret[OSC_SUPPORT_DWORD] &

OSC_SB_PCLPI_SUPPORT;

quoted

-               }
+
+       if (ACPI_FAILURE(acpi_run_osc(handle, &context)))
+               return;
+
+       capbuf_ret = context.ret.pointer;
+       if (context.ret.length <= OSC_SUPPORT_DWORD) {
                kfree(context.ret.pointer);
+               return;
        }
-       /* do we need to check other returned cap? Sounds no */
+
+       /*
+        * Now run _OSC again with query flag clean and with the caps

s/clean/clear/

quoted

+        * both platform and OS supports.

s/both platform and OS supports/supported by both the OS and the platform/

quoted

+        */
+       capbuf[OSC_QUERY_DWORD] = 0;
+       capbuf[OSC_SUPPORT_DWORD] = capbuf_ret[OSC_SUPPORT_DWORD];
+       kfree(context.ret.pointer);
+
+       if (ACPI_FAILURE(acpi_run_osc(handle, &context)))
+               return;
+
+       capbuf_ret = context.ret.pointer;
+       if (context.ret.length > OSC_SUPPORT_DWORD) {
+               osc_sb_apei_support_acked =
+                       capbuf_ret[OSC_SUPPORT_DWORD] & OSC_SB_APEI_SUPPORT;
+               osc_pc_lpi_support_confirmed =
+                       capbuf_ret[OSC_SUPPORT_DWORD] &

OSC_SB_PCLPI_SUPPORT;

quoted

+       }
+
+       kfree(context.ret.pointer);
 }

 /* ------------------------------------------------------------------------

--

quoted

@@ -1168,7 +1187,7 @@ static int __init acpi_bus_init(void)
         * _OSC method may exist in module level code,
         * so it must be run after ACPI_FULL_INITIALIZATION
         */
-       acpi_bus_osc_support();
+       acpi_bus_osc_negotiate_platform_control();

        /*
         * _PDC control method may load dynamic SSDT tables,
--

2.29.2