[PATCH v2] drivers/soc/litex: Add restart handler

[Geert Uytterhoeven <geert@linux-m68k.org>]

Let the LiteX SoC Controller a register a restart handler, which resets
the LiteX SoC by writing 1 to CSR_CTRL_RESET_ADDR.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
---
Tested with linux-on-litex-vexriscv.

This patch is based on upstream, i.e. not on top of Gabriel Somlo's
"[PATCH v5 0/4] drivers/soc/litex: support 32-bit subregisters, 64-bit
CPUs"
(https://lore.kernel.org/lkml/20201227161320.2194830-1-gsomlo@gmail.com/)

v2:
  - Rebase on top of v5.11-rc1,
  - Change reset handler priority to recommended default value of 128
    (was 192).

(v1 was not sent to a mailing list)
---
 drivers/soc/litex/litex_soc_ctrl.c | 33 +++++++++++++++++++++++++++---
 1 file changed, 30 insertions(+), 3 deletions(-)

diff --git a/drivers/soc/litex/litex_soc_ctrl.c b/drivers/soc/litex/litex_soc_ctrl.c
index 1217cafdfd4d1d2b..d729ad50d4ffca5e 100644
--- a/drivers/soc/litex/litex_soc_ctrl.c
+++ b/drivers/soc/litex/litex_soc_ctrl.c
@@ -15,6 +15,11 @@
 #include <linux/module.h>
 #include <linux/errno.h>
 #include <linux/io.h>
+#include <linux/reboot.h>
+
+/* reset register located at the base address */
+#define RESET_REG_OFF           0x00
+#define RESET_REG_VALUE         0x00000001
 
 /*
  * LiteX SoC Generator, depending on the configuration, can split a single
@@ -136,8 +141,20 @@ static int litex_check_csr_access(void __iomem *reg_addr)
 	return 0;
 }
 
-struct litex_soc_ctrl_device {
+static struct litex_soc_ctrl_device {
 	void __iomem *base;
+} *soc_ctrl_dev;
+
+static int litex_reset_handler(struct notifier_block *this, unsigned long mode,
+			       void *cmd)
+{
+	litex_write32(soc_ctrl_dev->base + RESET_REG_OFF, RESET_REG_VALUE);
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block litex_reset_nb = {
+	.notifier_call = litex_reset_handler,
+	.priority = 128,
 };
 
 static const struct of_device_id litex_soc_ctrl_of_match[] = {
@@ -149,7 +166,7 @@ MODULE_DEVICE_TABLE(of, litex_soc_ctrl_of_match);
 
 static int litex_soc_ctrl_probe(struct platform_device *pdev)
 {
-	struct litex_soc_ctrl_device *soc_ctrl_dev;
+	int error;
 
 	soc_ctrl_dev = devm_kzalloc(&pdev->dev, sizeof(*soc_ctrl_dev), GFP_KERNEL);
 	if (!soc_ctrl_dev)
@@ -159,7 +176,17 @@ static int litex_soc_ctrl_probe(struct platform_device *pdev)
 	if (IS_ERR(soc_ctrl_dev->base))
 		return PTR_ERR(soc_ctrl_dev->base);
 
-	return litex_check_csr_access(soc_ctrl_dev->base);
+	error = litex_check_csr_access(soc_ctrl_dev->base);
+	if (error)
+		return error;
+
+	error = register_restart_handler(&litex_reset_nb);
+	if (error) {
+		dev_warn(&pdev->dev, "cannot register restart handler: %d\n",
+			 error);
+	}
+
+	return 0;
 }
 
 static struct platform_driver litex_soc_ctrl_driver = {
-- 
2.25.1