Commit 46abe13b authored Aug 03, 2021 by Igor Skalkin Committed by Sudeep Holla Aug 05, 2021

firmware: arm_scmi: Add virtio transport

This transport enables communications with an SCMI platform through virtio;
the SCMI platform will be represented by a virtio device.

Implement an SCMI virtio driver according to the virtio SCMI device spec
[1]. Virtio device id 32 has been reserved for the SCMI device [2].

The virtio transport has one Tx channel (virtio cmdq, A2P channel) and
at most one Rx channel (virtio eventq, P2A channel).

The following feature bit defined in [1] is not implemented:
VIRTIO_SCMI_F_SHARED_MEMORY.

The number of messages which can be pending simultaneously is restricted
according to the virtqueue capacity negotiated at probing time.

As soon as Rx channel message buffers are allocated or have been read
out by the arm-scmi driver, feed them back to the virtio device.

Since some virtio devices may not have the short response time exhibited
by SCMI platforms using other transports, set a generous response
timeout.

SCMI polling mode is not supported by this virtio transport since deemed
meaningless: polling mode operation is offered by the SCMI core to those
transports that could not provide a completion interrupt on the TX path,
which is never the case for virtio whose core callbacks can easily call
into core scmi_rx_callback upon messages reception.

[1] https://github.com/oasis-tcs/virtio-spec/blob/master/virtio-scmi.tex
[2] https://www.oasis-open.org/committees/ballot.php?id=3496

Link: https://lore.kernel.org/r/20210803131024.40280-16-cristian.marussi@arm.com


Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Co-developed-by: Peter Hilber <peter.hilber@opensynergy.com>
Co-developed-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Igor Skalkin <igor.skalkin@opensynergy.com>
[ Peter: Adapted patch for submission to upstream. ]
Signed-off-by: Peter Hilber <peter.hilber@opensynergy.com>
[ Cristian: simplified driver logic, changed link_supplier and channel
	    available/setup logic, removed dummy callbacks ]
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

parent 13fba878

MAINTAINERS

+1 −0

Original line number	Diff line number	Diff line
		@@ -17940,6 +17940,7 @@ F: drivers/regulator/scmi-regulator.c
		F: drivers/reset/reset-scmi.c
		F: include/linux/sc[mp]i_protocol.h
		F: include/trace/events/scmi.h
		F: include/uapi/linux/virtio_scmi.h

		SYSTEM RESET/SHUTDOWN DRIVERS
		M: Sebastian Reichel <sre@kernel.org>

drivers/firmware/arm_scmi/Kconfig

+11 −0

Original line number	Diff line number	Diff line
		@@ -66,6 +66,17 @@ config ARM_SCMI_TRANSPORT_SMC
		If you want the ARM SCMI PROTOCOL stack to include support for a
		transport based on SMC, answer Y.

		config ARM_SCMI_TRANSPORT_VIRTIO
		bool "SCMI transport based on VirtIO"
		depends on VIRTIO
		select ARM_SCMI_HAVE_TRANSPORT
		select ARM_SCMI_HAVE_MSG
		help
		This enables the virtio based transport for SCMI.

		If you want the ARM SCMI PROTOCOL stack to include support for a
		transport based on VirtIO, answer Y.

		endif #ARM_SCMI_PROTOCOL

		config ARM_SCMI_POWER_DOMAIN

drivers/firmware/arm_scmi/Makefile

+1 −0

Original line number	Diff line number	Diff line
		@@ -5,6 +5,7 @@ scmi-transport-$(CONFIG_ARM_SCMI_HAVE_SHMEM) = shmem.o
		scmi-transport-$(CONFIG_ARM_SCMI_TRANSPORT_MAILBOX) += mailbox.o
		scmi-transport-$(CONFIG_ARM_SCMI_TRANSPORT_SMC) += smc.o
		scmi-transport-$(CONFIG_ARM_SCMI_HAVE_MSG) += msg.o
		scmi-transport-$(CONFIG_ARM_SCMI_TRANSPORT_VIRTIO) += virtio.o
		scmi-protocols-y = base.o clock.o perf.o power.o reset.o sensors.o system.o voltage.o
		scmi-module-objs := $(scmi-bus-y) $(scmi-driver-y) $(scmi-protocols-y) \
		$(scmi-transport-y)

drivers/firmware/arm_scmi/common.h

+3 −0

Original line number	Diff line number	Diff line
		@@ -418,6 +418,9 @@ extern const struct scmi_desc scmi_mailbox_desc;
		#ifdef CONFIG_ARM_SCMI_TRANSPORT_SMC
		extern const struct scmi_desc scmi_smc_desc;
		#endif
		#ifdef CONFIG_ARM_SCMI_TRANSPORT_VIRTIO
		extern const struct scmi_desc scmi_virtio_desc;
		#endif

		void scmi_rx_callback(struct scmi_chan_info cinfo, u32 msg_hdr, void priv);
		void scmi_free_channel(struct scmi_chan_info cinfo, struct idr idr, int id);

drivers/firmware/arm_scmi/driver.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -1983,6 +1983,9 @@ static const struct of_device_id scmi_of_match[] = {
		#endif
		#ifdef CONFIG_ARM_SCMI_TRANSPORT_SMC
		{ .compatible = "arm,scmi-smc", .data = &scmi_smc_desc},
		#endif
		#ifdef CONFIG_ARM_SCMI_TRANSPORT_VIRTIO
		{ .compatible = "arm,scmi-virtio", .data = &scmi_virtio_desc},
		#endif
		{ /* Sentinel */ },
		};