Subject: [PATCH v6] soc: at91: Add Atmel SFR SN (Serial Number) support

From: Kamel Bouhara <[email-masked]>
Date: Fri, 4 Oct 2019 17:18:02 +0200

Add support to read SFR's read-only registers providing the SoC
Serial Numbers (SN0+SN1) to userspace.

~ #  hexdump -n 8  -e'"%d\n"' /sys/bus/nvmem/devices/atmel-sfr0/nvmem
959527243
371539274

Signed-off-by: Kamel Bouhara <[email-masked]>
Tested-by: Tudor Ambarus <[email-masked]>
Reviewed-by: Tudor Ambarus <[email-masked]>
---
Changes in v2:
 - updated atmel-sfr.c to sfr.c in Makefile
 - fixed missing drvdata struct definition
 - added missing syscon header
Changes in v3:
 - Fixed typo: processor in Kconfig
 - Renamed private struct sfr_priv to atmel_sfr_priv
 - Dropped the drvdata structure as we have same size for both SN
   registers in SAMA5D2/4, just hardcoded it for now.
 - Cleaned up private struct from unused members
 - Fixed misusage of devm_kzalloc
Changes in v5:
 - Removed the blankline at EOF
 - Feeded the entropy pool with the SoC SN using add_device_randomness()
   and do it only once at probe().
Changes in v6:
 - Fixed missing return of a possible error from atmel_sfr_read()
 - Added T-b and R-b tags

 drivers/soc/atmel/Kconfig  | 11 +++++
 drivers/soc/atmel/Makefile |  1 +
 drivers/soc/atmel/sfr.c    | 99 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 111 insertions(+)
 create mode 100644 drivers/soc/atmel/sfr.c

diff --git a/drivers/soc/atmel/Kconfig b/drivers/soc/atmel/Kconfig
index 05528139b023..50caf6db9c0e 100644
--- a/drivers/soc/atmel/Kconfig
+++ b/drivers/soc/atmel/Kconfig
@@ -5,3 +5,14 @@ config AT91_SOC_ID
 	default ARCH_AT91
 	help
 	  Include support for the SoC bus on the Atmel ARM SoCs.
+
+config AT91_SOC_SFR
+	tristate "Special Function Registers support"
+	depends on ARCH_AT91 || COMPILE_TEST
+	help
+	  This is a driver for the Special Function Registers available on
+	  Atmel SAMA5Dx SoCs, providing access to specific aspects of the
+	  integrated memory, bridge implementations, processor etc.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called sfr.
diff --git a/drivers/soc/atmel/Makefile b/drivers/soc/atmel/Makefile
index 7ca355d10553..d849a897cd77 100644
--- a/drivers/soc/atmel/Makefile
+++ b/drivers/soc/atmel/Makefile
@@ -1,2 +1,3 @@
 # SPDX-License-Identifier: GPL-2.0-only
 obj-$(CONFIG_AT91_SOC_ID) += soc.o
+obj-$(CONFIG_AT91_SOC_SFR) += sfr.o
diff --git a/drivers/soc/atmel/sfr.c b/drivers/soc/atmel/sfr.c
new file mode 100644
index 000000000000..0525eef49d1a
--- /dev/null
+++ b/drivers/soc/atmel/sfr.c
@@ -0,0 +1,99 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * sfr.c - driver for special function registers
+ *
+ * Copyright (C) 2019 Bootlin.
+ *
+ */
+#include <linux/mfd/syscon.h>
+#include <linux/module.h>
+#include <linux/nvmem-provider.h>
+#include <linux/random.h>
+#include <linux/of.h>
+#include <linux/of_device.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+
+#define SFR_SN0		0x4c
+#define SFR_SN_SIZE	8
+
+struct atmel_sfr_priv {
+	struct regmap			*regmap;
+};
+
+static int atmel_sfr_read(void *context, unsigned int offset,
+			  void *buf, size_t bytes)
+{
+	struct atmel_sfr_priv *priv = context;
+
+	return regmap_bulk_read(priv->regmap, SFR_SN0 + offset,
+				buf, bytes / 4);
+}
+
+static struct nvmem_config atmel_sfr_nvmem_config = {
+	.name = "atmel-sfr",
+	.read_only = true,
+	.word_size = 4,
+	.stride = 4,
+	.size = SFR_SN_SIZE,
+	.reg_read = atmel_sfr_read,
+};
+
+static int atmel_sfr_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct device_node *np = dev->of_node;
+	struct nvmem_device *nvmem;
+	struct atmel_sfr_priv *priv;
+	u8 sn[SFR_SN_SIZE];
+	int ret;
+
+	priv = devm_kmalloc(dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->regmap = syscon_node_to_regmap(np);
+	if (IS_ERR(priv->regmap)) {
+		dev_err(dev, "cannot get parent's regmap\n");
+		return PTR_ERR(priv->regmap);
+	}
+
+	atmel_sfr_nvmem_config.dev = dev;
+	atmel_sfr_nvmem_config.priv = priv;
+
+	nvmem = devm_nvmem_register(dev, &atmel_sfr_nvmem_config);
+	if (IS_ERR(nvmem)) {
+		dev_err(dev, "error registering nvmem config\n");
+		return PTR_ERR(nvmem);
+	}
+
+	ret = atmel_sfr_read(priv, 0, sn, SFR_SN_SIZE);
+	if (ret == 0)
+		add_device_randomness(sn, SFR_SN_SIZE);
+
+	return ret;
+}
+
+static const struct of_device_id atmel_sfr_dt_ids[] = {
+	{
+		.compatible = "atmel,sama5d2-sfr",
+	}, {
+		.compatible = "atmel,sama5d4-sfr",
+	}, {
+		/* sentinel */
+	},
+};
+MODULE_DEVICE_TABLE(of, atmel_sfr_dt_ids);
+
+static struct platform_driver atmel_sfr_driver = {
+	.probe = atmel_sfr_probe,
+	.driver = {
+		.name = "atmel-sfr",
+		.of_match_table = atmel_sfr_dt_ids,
+	},
+};
+module_platform_driver(atmel_sfr_driver);
+
+MODULE_AUTHOR("Kamel Bouhara <[email-masked]>");
+MODULE_DESCRIPTION("Atmel SFR SN driver for SAMA5D2/4 SoC family");
+MODULE_LICENSE("GPL v2");
--
2.23.0

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