[PATCH 4/5] rtc: Add basic support for RTC via Surface System Aggregator Module

[Val Packett <val@packett.cool>]

From: Maximilian Luz <luzmaximilian@gmail.com>

The Surface Pro X uses an RTC provided by the SSAM. Add a driver for it.

Signed-off-by: Maximilian Luz <luzmaximilian@gmail.com>
Signed-off-by: Val Packett <val@packett.cool>
---
 MAINTAINERS               |   8 +++
 drivers/rtc/Kconfig       |   9 +++
 drivers/rtc/Makefile      |   1 +
 drivers/rtc/rtc-surface.c | 129 ++++++++++++++++++++++++++++++++++++++
 4 files changed, 147 insertions(+)
 create mode 100644 drivers/rtc/rtc-surface.c

diff --git a/MAINTAINERS b/MAINTAINERS
index d23f7d8c4c17..36b3abad50f4 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -18585,6 +18585,14 @@ L:	platform-driver-x86@vger.kernel.org
 S:	Supported
 F:	drivers/platform/surface/surfacepro3_button.c
 
+MICROSOFT SURFACE PRO X RTC DRIVER
+M:	Maximilian Luz <luzmaximilian@gmail.com>
+M:	Val Packett <val@packett.cool>
+L:	linux-rtc@vger.kernel.org
+L:	linux-arm-msm@vger.kernel.org
+S:	Maintained
+F:	drivers/rtc/rtc-surface.c
+
 MICROSOFT SURFACE SYSTEM AGGREGATOR HUB DRIVER
 M:	Maximilian Luz <luzmaximilian@gmail.com>
 L:	platform-driver-x86@vger.kernel.org
diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index 73ec9230edfd..6af1aa18724f 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -1451,6 +1451,15 @@ config RTC_DRV_NTXEC
 	  embedded controller found in certain e-book readers designed by the
 	  original design manufacturer Netronix.
 
+config RTC_DRV_SURFACE
+	tristate "Microsoft Surface Aggregator RTC"
+	depends on SURFACE_AGGREGATOR
+	depends on SURFACE_AGGREGATOR_BUS
+	help
+	  Say yes here if you want to support the RTC functionality of the
+	  Surface Aggregator Module (embedded controller) found in the
+	  Microsoft Surface Pro X tablet.
+
 comment "on-CPU RTC drivers"
 
 config RTC_DRV_ASM9260
diff --git a/drivers/rtc/Makefile b/drivers/rtc/Makefile
index 46f1a0fc2416..f86e827c14e0 100644
--- a/drivers/rtc/Makefile
+++ b/drivers/rtc/Makefile
@@ -186,6 +186,7 @@ obj-$(CONFIG_RTC_DRV_SUN4V)	+= rtc-sun4v.o
 obj-$(CONFIG_RTC_DRV_SUN6I)	+= rtc-sun6i.o
 obj-$(CONFIG_RTC_DRV_SUNPLUS)	+= rtc-sunplus.o
 obj-$(CONFIG_RTC_DRV_SUNXI)	+= rtc-sunxi.o
+obj-$(CONFIG_RTC_DRV_SURFACE)	+= rtc-surface.o
 obj-$(CONFIG_RTC_DRV_TEGRA)	+= rtc-tegra.o
 obj-$(CONFIG_RTC_DRV_TEST)	+= rtc-test.o
 obj-$(CONFIG_RTC_DRV_TI_K3)	+= rtc-ti-k3.o
diff --git a/drivers/rtc/rtc-surface.c b/drivers/rtc/rtc-surface.c
new file mode 100644
index 000000000000..f6c17c4e98d5
--- /dev/null
+++ b/drivers/rtc/rtc-surface.c
@@ -0,0 +1,129 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * AC driver for 7th-generation Microsoft Surface devices via Surface System
+ * Aggregator Module (SSAM).
+ *
+ * Copyright (C) 2019-2021 Maximilian Luz <luzmaximilian@gmail.com>
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/rtc.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+
+#include <linux/surface_aggregator/device.h>
+
+struct surface_rtc {
+	struct ssam_device *sdev;
+	struct rtc_device *rtc;
+};
+
+SSAM_DEFINE_SYNC_REQUEST_R(__ssam_rtc_get_unix_time, __le32, {
+	.target_category = SSAM_SSH_TC_SAM,
+	.target_id       = SSAM_SSH_TID_SAM,
+	.instance_id     = 0x00,
+	.command_id      = 0x10,
+});
+
+SSAM_DEFINE_SYNC_REQUEST_W(__ssam_rtc_set_unix_time, __le32, {
+	.target_category = SSAM_SSH_TC_SAM,
+	.target_id       = SSAM_SSH_TID_SAM,
+	.instance_id     = 0x00,
+	.command_id      = 0x0f,
+});
+
+static int ssam_rtc_get_unix_time(struct surface_rtc *srtc, u32 *time)
+{
+	__le32 time_le;
+	int status;
+
+	status = __ssam_rtc_get_unix_time(srtc->sdev->ctrl, &time_le);
+	if (status)
+		return status;
+
+	*time = le32_to_cpu(time_le);
+	return 0;
+}
+
+static int ssam_rtc_set_unix_time(struct surface_rtc *srtc, u32 time)
+{
+	__le32 time_le = cpu_to_le32(time);
+
+	return __ssam_rtc_set_unix_time(srtc->sdev->ctrl, &time_le);
+}
+
+static int surface_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct surface_rtc *srtc = dev_get_drvdata(dev);
+	int status;
+	u32 time;
+
+	status = ssam_rtc_get_unix_time(srtc, &time);
+	if (status)
+		return status;
+
+	rtc_time64_to_tm(time, tm);
+	return 0;
+}
+
+static int surface_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct surface_rtc *srtc = dev_get_drvdata(dev);
+	time64_t time = rtc_tm_to_time64(tm);
+
+	return ssam_rtc_set_unix_time(srtc, (u32)time);
+}
+
+static const struct rtc_class_ops surface_rtc_ops = {
+	.read_time = surface_rtc_read_time,
+	.set_time = surface_rtc_set_time,
+};
+
+static int surface_rtc_probe(struct ssam_device *sdev)
+{
+	struct surface_rtc *srtc;
+
+	srtc = devm_kzalloc(&sdev->dev, sizeof(*srtc), GFP_KERNEL);
+	if (!srtc)
+		return -ENOMEM;
+
+	srtc->sdev = sdev;
+
+	srtc->rtc = devm_rtc_allocate_device(&sdev->dev);
+	if (IS_ERR(srtc->rtc))
+		return PTR_ERR(srtc->rtc);
+
+	srtc->rtc->ops = &surface_rtc_ops;
+	srtc->rtc->range_max = U32_MAX;
+
+	ssam_device_set_drvdata(sdev, srtc);
+
+	return devm_rtc_register_device(srtc->rtc);
+}
+
+static void surface_rtc_remove(struct ssam_device *sdev)
+{
+	/* Device-managed allocations take care of everything... */
+}
+
+static const struct ssam_device_id surface_rtc_match[] = {
+	{ SSAM_SDEV(SAM, SAM, 0x00, 0x00) },
+	{ },
+};
+MODULE_DEVICE_TABLE(ssam, surface_rtc_match);
+
+static struct ssam_device_driver surface_rtc_driver = {
+	.probe = surface_rtc_probe,
+	.remove = surface_rtc_remove,
+	.match_table = surface_rtc_match,
+	.driver = {
+		.name = "surface_rtc",
+		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
+	},
+};
+module_ssam_device_driver(surface_rtc_driver);
+
+MODULE_AUTHOR("Maximilian Luz <luzmaximilian@gmail.com>");
+MODULE_DESCRIPTION("RTC driver for Surface System Aggregator Module");
+MODULE_LICENSE("GPL");
-- 
2.56.0