skiboot: Find the IMC DTB

IMC (In Memory Collection) catalog is a repository of information
about the Performance Monitoring Units (PMUs) and their events under
the IMC infrastructure. The information include :
 - The PMU names
 - Event names
 - Event description
 - Event offsets
 - Event scale
 - Event unit

The catalog is provided as a flattened device tree (dtb). Processors
with different PVR values may have different PMU or event names. Hence,
for each processor, there can be multiple device tree binaries (dtbs)
containing the IMC information. Each of the dtb is compressed and forms
a sub-partition inside the PNOR partition "IMA_CATALOG". Here is a link
to the commit adding this partition to PNOR :
https://github.com/open-power/pnor/commit/c940142c6dc64dd176096dc648f433c889919e84

So, each compressed dtb forms a sub-partition inside the IMC pnor
partition and can be accessed/loaded through a sub-partition id which
is nothing but the PVR id. Based on the current processor's PVR, the
appropriate sub-partion will be loaded.

Note however, that the catalog information is in the form of a dtb and
the dtb is compressed too. So, the sub-partition loaded must be
decompressed first before we can actually use it.

It is important to mention here that while a PNOR image built for one
processor is specific to only that processor and isn't portable, a
single system generation (Processor version) may have multiple revisions
and these revisions may have some changes in their IMC PMUs and events,
and hence, the need for multiple IMC DTBs.

The sub-partition that we obtain from the IMC pnor partition is a
compressed device tree binary. We uncompress it using the libxz's
functions. After uncompressing it, we link the device tree binary to the
system's device tree. The kernel can now access the device tree and get
the IMC PMUs and their events' information.

Not all the IMC PMUs listed in the device tree may be available. This is
indicated by imc availability vector (which is a part of the IMC control
block structure). We need to check this vector and make sure to remove
the IMC device nodes which are unavailable.

Signed-off-by: Hemant Kumar <hemant@linux.vnet.ibm.com>
Signed-off-by: Anju T Sudhakar <anju@linux.vnet.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
[stewart@linux.vnet.ibm.com: use pr_fmt, fix failure path for resource load]
Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>

0 files changed, 0 insertions, 0 deletions