AMD MP2 STB function provides a data buffer used to log debug information
about the system execution during S2Idle suspend/resume.

A data buffer known as the STB (Smart Trace Buffer) is a circular buffer
which is a low-level log to assist in debugging by providing insights
into any potential hangs or stalls that may occur during the S2Idle
suspend/resume processes.

The current PMC driver retrieves STB data from MP1, but there can be
scenarios where MP1 might hang or become unresponsive, leading to the
loss of critical data present in the STB buffer. This defeats the purpose
of the STB buffer, which was originally meant to help identify system
failures.

This feature creates stb_read_previous_boot debugfs allows users to
retrieve the STB log from MP2 specifically from the last occurrence of
the S2Idle suspend/resume. A userspace daemon can access STB log of last
S2Idle suspend/resume which can help to troubleshoot potential issues
related to hangs or stalls during the S2Idle suspend/resume sequence.
Reviewed-by: Shyam Sundar S K <Shyam-sundar.S-k@amd.com>
Signed-off-by: Basavaraj Natikar <Basavaraj.Natikar@amd.com>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Link: https://lore.kernel.org/r/20240404090702.325838-1-Basavaraj.Natikar@amd.comSigned-off-by: Hans de Goede <hdegoede@redhat.com>