linux-kernel - [PATCH v5 09/13] firmware: arm_scmi: Add atomic mode support to virtio transport

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Date:   Thu, 23 Sep 2021 15:57:58 +0100
From:   Cristian Marussi <cristian.marussi@....com>
To:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Cc:     sudeep.holla@....com, james.quinlan@...adcom.com,
        Jonathan.Cameron@...wei.com, f.fainelli@...il.com,
        etienne.carriere@...aro.org, vincent.guittot@...aro.org,
        souvik.chakravarty@....com, peter.hilber@...nsynergy.com,
        igor.skalkin@...nsynergy.com, cristian.marussi@....com
Subject: [PATCH v5 09/13] firmware: arm_scmi: Add atomic mode support to virtio transport

SCMI virtio transport support does not contain any sleeping pattern, so
declare it as .atomic_capable.

Add a Kernel configuration option to enable SCMI VirtIO transport atomic
mode operation and leave it as default disabled.

Signed-off-by: Cristian Marussi <cristian.marussi@....com>
---
v4 --> v5
- add CONFIG_ARM_SCMI_TRANSPORT_VIRTIO_ATOMIC_ENABLE
- reviewed commit message
---
 drivers/firmware/arm_scmi/Kconfig  | 14 ++++++++++++++
 drivers/firmware/arm_scmi/virtio.c |  2 ++
 2 files changed, 16 insertions(+)

diff --git a/drivers/firmware/arm_scmi/Kconfig b/drivers/firmware/arm_scmi/Kconfig
index 62517417848b..0bea0c4d9db1 100644
--- a/drivers/firmware/arm_scmi/Kconfig
+++ b/drivers/firmware/arm_scmi/Kconfig
@@ -87,6 +87,20 @@ config ARM_SCMI_TRANSPORT_VIRTIO
 	  If you want the ARM SCMI PROTOCOL stack to include support for a
 	  transport based on VirtIO, answer Y.
 
+config ARM_SCMI_TRANSPORT_VIRTIO_ATOMIC_ENABLE
+	bool "Enable atomic mode for SCMI VirtIO transport"
+	depends on ARM_SCMI_TRANSPORT_VIRTIO
+	help
+	  Enable atomic mode of operation for SCMI VirtIO based transport.
+
+	  If you want the SCMI VirtIO based transport to operate in atomic
+	  mode, avoiding any kind of sleeping behaviour on the TX path, both
+	  by the transport and by the SCMI core, answer Y.
+	  Enabling atomic mode operations allows any SCMI driver using this
+	  transport to operate in atomic context too, at the price of using
+	  a number of busy-waiting primitives all over instead.
+	  If unsure say N.
+
 endif #ARM_SCMI_PROTOCOL
 
 config ARM_SCMI_POWER_DOMAIN
diff --git a/drivers/firmware/arm_scmi/virtio.c b/drivers/firmware/arm_scmi/virtio.c
index 8941bb40f2df..fb3c2760ed42 100644
--- a/drivers/firmware/arm_scmi/virtio.c
+++ b/drivers/firmware/arm_scmi/virtio.c
@@ -488,4 +488,6 @@ const struct scmi_desc scmi_virtio_desc = {
 	.max_rx_timeout_ms = 60000, /* for non-realtime virtio devices */
 	.max_msg = 0, /* overridden by virtio_get_max_msg() */
 	.max_msg_size = VIRTIO_SCMI_MAX_MSG_SIZE,
+	.atomic_capable = true,
+	.atomic_enabled = IS_ENABLED(CONFIG_ARM_SCMI_TRANSPORT_VIRTIO_ATOMIC_ENABLE),
 };
-- 
2.17.1