[PATCH v5 4/4] proc_pid_fdinfo.5: Add DRM subsection

[Ian Rogers <irogers@google.com>]

Add description of DRM fdinfo information based on the Linux kernel's
`Documentation/gpu/drm-usage-stats.rst`:
https://docs.kernel.org/gpu/drm-usage-stats.html
---
v5. Update style a suggested-by G. Branden Robinson
    <g.branden.robinson@gmail.com>
---
 man/man5/proc_pid_fdinfo.5 | 107 +++++++++++++++++++++++++++++++++++++
 1 file changed, 107 insertions(+)

diff --git a/man/man5/proc_pid_fdinfo.5 b/man/man5/proc_pid_fdinfo.5
index c4914f1f3..bb77ee9a7 100644
--- a/man/man5/proc_pid_fdinfo.5
+++ b/man/man5/proc_pid_fdinfo.5
@@ -300,6 +300,113 @@ fields contain the values that
 .BR timerfd_gettime (2)
 on this file descriptor would return.)
 .RE
+.SS Direct Rendering Manager
+.P
+DRM drivers can optionally choose to expose usage stats through
+/proc/pid/fdinfo/. For example:
+.P
+.in +4n
+.EX
+pos:    0
+flags:  02100002
+mnt_id: 26
+ino:    284
+drm-driver:     i915
+drm-client-id:  39
+drm-pdev:       0000:00:02.0
+drm-total-system0:      6044 KiB
+drm-shared-system0:     0
+drm-active-system0:     0
+drm-resident-system0:   6044 KiB
+drm-purgeable-system0:  1688 KiB
+drm-total-stolen-system0:       0
+drm-shared-stolen-system0:      0
+drm-active-stolen-system0:      0
+drm-resident-stolen-system0:    0
+drm-purgeable-stolen-system0:   0
+drm-engine-render:      346249 ns
+drm-engine-copy:        0 ns
+drm-engine-video:       0 ns
+drm-engine-capacity-video:      2
+drm-engine-video-enhance:       0 ns
+.EE
+.TP
+.BR drm\-driver: " .+  (mandatory)"
+The name this driver registered.
+.TP
+.BR drm\-pdev: " [0-9A-F]{4}:[0-9A-F]{2}:[0-9A-F]{2}.[0-9A-F]"
+For PCI devices this should contain the PCI slot address of the device
+in question.
+.TP
+.BR drm\-client-id: " [0-9]+"
+Unique value relating to the open DRM file descriptor used to
+distinguish duplicated and shared file descriptors.
+.P
+GPUs usually contain multiple execution engines. Each shall be given a
+stable and unique name
+.IR engine-name ,
+with possible values documented in the driver specific documentation.
+.TP
+.BI drm\-engine\- engine-name :\c
+\& [0-9]+ ns
+GPU engine utilization, time spent busy executing workloads for this client.
+.TP
+.BI drm\-engine\-capacity\- engine-name :\c
+\& [0-9]+
+Capacity of the engine if not 1, cannot be 0.
+.TP
+.BI drm\-cycles\- engine-name :\c
+\& [0-9]+
+Contains the number of busy cycles for the given engine.  Values are
+not required to be constantly monotonic, but are required to catch up
+with the previously reported larger value within a reasonable
+period. Upon observing a value lower than what was previously read,
+userspace is expected to stay with that larger previous value until a
+monotonic update is seen.
+.TP
+.BI drm\-total\-cycles\- engine-name :\c
+\& [0-9]+
+Contains the total number cycles for the given engine.  This is a
+timestamp in GPU unspecified unit that matches the update rate of
+drm\-cycles\-\fIengine-name\fP.
+For drivers that implement this interface,
+the engine utilization can be calculated entirely on the GPU clock
+domain, without considering the CPU sleep time between 2 samples.
+.P
+Each possible memory type which can be used to store buffer objects by
+the GPU in question shall be given a stable and unique name
+.IR region .
+The name "memory" is reserved to refer to normal system memory.
+.TP
+.BI drm\-memory\- region :\c
+\& [0-9]+ [KiB|MiB]
+The amount of storage currently consumed by the buffer objects belong
+to this client, in the respective memory region.
+.IP
+Default unit shall be bytes with optional unit specifiers of 'KiB' or 'MiB'
+indicating kibi- or mebi-bytes.
+.TP
+.BI drm\-shared\- region :\c
+\& [0-9]+ [KiB|MiB]
+The total size of buffers that are shared with another file (e.g., have more
+than a single handle).
+.TP
+.BI drm\-total\- region :\c
+\& [0-9]+ [KiB|MiB]
+The total size of buffers that including shared and private memory.
+.TP
+.BI drm\-resident\- region :\c
+\& [0-9]+ [KiB|MiB]
+The total size of buffers that are resident in the specified region.
+.TP
+.BI drm\-purgeable\- region :\c
+\& [0-9]+ [KiB|MiB]
+The total size of buffers that are purgeable.
+.TP
+.BI drm\-active\- region :\c
+\& [0-9]+ [KiB|MiB]
+The total size of buffers that are active on one or more engines.
+
 .SH HISTORY
 Linux 2.6.22.
 .SH SEE ALSO
-- 
2.47.0.338.g60cca15819-goog