linux-kernel - [PATCH v2 5/7] firmware: arm_scmi: Make use of FastChannels configurable

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Date:   Mon,  6 Jun 2022 11:02:28 +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,
        daniel.lezcano@...aro.org, tarek.el-sherbiny@....com,
        adrian.slatineanu@....com, souvik.chakravarty@....com,
        wleavitt@...vell.com, wbartczak@...vell.com,
        Cristian Marussi <cristian.marussi@....com>
Subject: [PATCH v2 5/7] firmware: arm_scmi: Make use of FastChannels configurable

Add a Kernel configuration entry used to optionally disable the usage of
SCMI FastChannels even on platforms where they are available.

Make such option default-yes to preserve the original SCMI system behaviour
of using any available FC.

Signed-off-by: Cristian Marussi <cristian.marussi@....com>
---
 drivers/firmware/arm_scmi/Kconfig    | 13 +++++++++++++
 drivers/firmware/arm_scmi/perf.c     |  3 ++-
 drivers/firmware/arm_scmi/powercap.c |  3 ++-
 3 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/drivers/firmware/arm_scmi/Kconfig b/drivers/firmware/arm_scmi/Kconfig
index 1e7b7fec97d9..624f32b61825 100644
--- a/drivers/firmware/arm_scmi/Kconfig
+++ b/drivers/firmware/arm_scmi/Kconfig
@@ -42,6 +42,19 @@ config ARM_SCMI_HAVE_MSG
 	  This declares whether a message passing based transport for SCMI is
 	  available.
 
+config ARM_SCMI_USE_FASTCHANNELS
+	bool "Use SCMI FastChannels when available"
+	default y
+	help
+	  Use SCMI FastChannels when advertised as available by the platform.
+
+	  On systems where the SCMI platform advertises the availability of
+	  FastChannels, supported SCMI commands can be issued triggering a
+	  one-way FastChannel request, much more quicker than using a
+	  regular SCMI message transfer.
+	  When set to N forces the OSPM to use instead regular SCMI message
+	  transfers even if FastChannels are available. If unsure say Y.
+
 config ARM_SCMI_TRANSPORT_MAILBOX
 	bool "SCMI transport based on Mailbox"
 	depends on MAILBOX
diff --git a/drivers/firmware/arm_scmi/perf.c b/drivers/firmware/arm_scmi/perf.c
index 587b334589b0..3c491b3aa0bd 100644
--- a/drivers/firmware/arm_scmi/perf.c
+++ b/drivers/firmware/arm_scmi/perf.c
@@ -820,7 +820,8 @@ static int scmi_perf_protocol_init(const struct scmi_protocol_handle *ph)
 		scmi_perf_domain_attributes_get(ph, domain, dom, version);
 		scmi_perf_describe_levels_get(ph, domain, dom);
 
-		if (dom->perf_fastchannels)
+		if (dom->perf_fastchannels &&
+		    IS_ENABLED(CONFIG_ARM_SCMI_USE_FASTCHANNELS))
 			scmi_perf_domain_init_fc(ph, domain, &dom->fc_info);
 	}
 
diff --git a/drivers/firmware/arm_scmi/powercap.c b/drivers/firmware/arm_scmi/powercap.c
index e9b4c34e1fb4..9e3a803d4f16 100644
--- a/drivers/firmware/arm_scmi/powercap.c
+++ b/drivers/firmware/arm_scmi/powercap.c
@@ -830,7 +830,8 @@ scmi_powercap_protocol_init(const struct scmi_protocol_handle *ph)
 		if (ret)
 			return ret;
 
-		if (pinfo->powercaps[domain].fastchannels)
+		if (pinfo->powercaps[domain].fastchannels &&
+		    IS_ENABLED(CONFIG_ARM_SCMI_USE_FASTCHANNELS))
 			scmi_powercap_domain_init_fc(ph, domain,
 						     &pinfo->powercaps[domain].fc_info);
 	}
-- 
2.32.0