[PATCH] cpufreq/amd-pstate: Do not fail init when auto_sel cannot be written

[Wentao Guan]

Since commit 9dfd13f80c85 ("cpufreq/amd-pstate: Toggle auto_sel in active
mode on shared memory systems"), shmem_init_perf() programs
AUTONOMOUS_SELECTION_ENABLE unconditionally, including in active mode.

On platforms implementing CPPC v2 and below, _CPC reports Autonomous
Selection Enable as a plain integer rather than as a register descriptor.
Such a field is a read-only capability flag: cppc_get_reg_val() reads it
back successfully (the firmware reports it as enabled), while
cppc_set_reg_val() rejects the write with -EOPNOTSUPP because the entry is
not an ACPI_TYPE_BUFFER.

shmem_init_perf() propagates that error, so every amd_pstate_epp_cpu_init()
fails, cpufreq_register_driver() ends up with an empty policy list and
returns -ENODEV, and amd-pstate refuses to load at all:

  amd_pstate: failed to set auto_sel, ret: -95
  amd_pstate: Failed to initialize CPU 0: -95
  ...
  amd_pstate: failed to register with return -19

Failing to write auto_sel is not fatal: the register is either already
enabled, as reported by the cppc_get_auto_sel() call right above, or not
writable at all, and active mode worked in both cases before the offending
commit.  Downgrade the failure to a warning and let initialization
continue, matching how the cppc_get_auto_sel() failure is handled.

Fixes: 9dfd13f80c85 ("cpufreq/amd-pstate: Toggle auto_sel in active mode on shared memory systems")
Cc: stable@xxxxxxxxxxxxxxx
Tested-by: LFRon <ronforever@xxxxxxxxxxx>
Signed-off-by: Wentao Guan <guanwentao@xxxxxxxxxxxxx>
---
 drivers/cpufreq/amd-pstate.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index 80d99ba1902c9..3657c5cccd4d8 100644
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -538,5 +538,5 @@ static int shmem_init_perf(struct amd_cpudata *cpudata)
 	if (ret)
 		pr_warn("failed to set auto_sel, ret: %d\n", ret);
 
-	return ret;
+	return 0;
 }