perf: arm_cspmu: nvidia: monitor all ports by default

Some NVIDIA PMUs like the NVLINK-C2C, CNVLINK, and PCIE PMU provide
port filtering. If the port filter is set to zero, the counter of
these PMUs will not capture any event. To avoid meaningless
experiment, the driver sets the port filter value to a default
non-zero value.

Signed-off-by: Besar Wicaksono <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Will Deacon <[e-mail]>

Documentation/admin-guide/perf/nvidia-pmu.rst

···
 The NVLink-C2C has two ports that can be connected to one GPU (occupying both
 ports) or to two GPUs (one GPU per port). The user can use "port" bitmap
 parameter to select the port(s) to monitor. Each bit represents the port number,
-e.g. "port=0x1" corresponds to port 0 and "port=0x3" is for port 0 and 1.
+e.g. "port=0x1" corresponds to port 0 and "port=0x3" is for port 0 and 1. The
+PMU will monitor both ports by default if not specified.
 
 Example for port filtering:
 
···
 The NVLink-C2C has two ports that can be connected to one GPU (occupying both
 ports) or to two GPUs (one GPU per port). The user can use "port" bitmap
 parameter to select the port(s) to monitor. Each bit represents the port number,
-e.g. "port=0x1" corresponds to port 0 and "port=0x3" is for port 0 and 1.
+e.g. "port=0x1" corresponds to port 0 and "port=0x3" is for port 0 and 1. The
+PMU will monitor both ports by default if not specified.
 
 Example for port filtering:
 
···
 Each SoC socket can be connected to one or more sockets via CNVLink. The user can
 use "rem_socket" bitmap parameter to select the remote socket(s) to monitor.
 Each bit represents the socket number, e.g. "rem_socket=0xE" corresponds to
-socket 1 to 3.
+socket 1 to 3. The PMU will monitor all remote sockets by default if not
+specified.
 /sys/bus/event_source/devices/nvidia_cnvlink_pmu_<socket-id>/format/rem_socket
 shows the valid bits that can be set in the "rem_socket" parameter.
 
···
 
 Each SoC socket can support multiple root ports. The user can use
 "root_port" bitmap parameter to select the port(s) to monitor, i.e.
-"root_port=0xF" corresponds to root port 0 to 3.
+"root_port=0xF" corresponds to root port 0 to 3. The PMU will monitor all root
+ports by default if not specified.
 /sys/bus/event_source/devices/nvidia_pcie_pmu_<socket-id>/format/root_port
 shows the valid bits that can be set in the "root_port" parameter.
 

drivers/perf/arm_cspmu/nvidia_cspmu.c

···
 	const struct nv_cspmu_ctx *ctx =
 		to_nv_cspmu_ctx(to_arm_cspmu(event->pmu));
 
-	if (ctx->filter_mask == 0)
+	const u32 filter_val = event->attr.config1 & ctx->filter_mask;
+
+	if (filter_val == 0)
 		return ctx->filter_default_val;
 
-	return event->attr.config1 & ctx->filter_mask;
+	return filter_val;
 }
 
 enum nv_cspmu_name_fmt {