power: reset: syscon-reboot: add gs101-specific reset

Linux supports a couple different reset modes, but this driver here
doesn't distinguish between them and issues the same syscon register
write irrespective of the reset mode requested by the kernel.

Since DTs should not encode register writes (see e.g. [1]), update this
driver to support different reset modes based on DT compatible match.

At the same time, add support for Google GS101, which does support
cold, hard, warm, and soft.

As an example why this is useful, other than properly supporting the
Linux reboot= kernel command line option or sysfs entry, this change
allows gs101-platforms to default to a more secure cold-reset, but also
to warm-reset in case RAM contents needs to be retained across the
reset.

Link: https://lore.kernel.org/all/20250227132644.GA1924628-robh@kernel.org/ [1]
Signed-off-by: André Draszik <andre.draszik@linaro.org>
Link: https://lore.kernel.org/r/20250401-syscon-reboot-reset-mode-v5-2-5b9357442363@linaro.org
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

Author: andred

drivers/power/reset/syscon-reboot.c

@@ -14,11 +14,24 @@
 #include <linux/reboot.h>
 #include <linux/regmap.h>
 
-struct syscon_reboot_context {
-	struct regmap *map;
+struct reboot_mode_bits {
 	u32 offset;
-	u32 value;
 	u32 mask;
+	u32 value;
+	bool valid;
+};
+
+struct reboot_data {
+	struct reboot_mode_bits mode_bits[REBOOT_SOFT + 1];
+	struct reboot_mode_bits catchall;
+};
+
+struct syscon_reboot_context {
+	struct regmap *map;
+
+	const struct reboot_data *rd; /* from of match data, if any */
+	struct reboot_mode_bits catchall; /* from DT */
+
 	struct notifier_block restart_handler;
 };
 
@@ -28,9 +41,21 @@ static int syscon_restart_handle(struct notifier_block *this,
 	struct syscon_reboot_context *ctx =
 			container_of(this, struct syscon_reboot_context,
 					restart_handler);
+	const struct reboot_mode_bits *mode_bits;
+
+	if (ctx->rd) {
+		if (mode < ARRAY_SIZE(ctx->rd->mode_bits) &&
+		    ctx->rd->mode_bits[mode].valid)
+			mode_bits = &ctx->rd->mode_bits[mode];
+		else
+			mode_bits = &ctx->rd->catchall;
+	} else {
+		mode_bits = &ctx->catchall;
+	}
 
 	/* Issue the reboot */
-	regmap_update_bits(ctx->map, ctx->offset, ctx->mask, ctx->value);
+	regmap_update_bits(ctx->map, mode_bits->offset, mode_bits->mask,
+			   mode_bits->value);
 
 	mdelay(1000);
 
@@ -42,7 +67,6 @@ static int syscon_reboot_probe(struct platform_device *pdev)
 {
 	struct syscon_reboot_context *ctx;
 	struct device *dev = &pdev->dev;
-	int mask_err, value_err;
 	int priority;
 	int err;
 
@@ -60,24 +84,33 @@ static int syscon_reboot_probe(struct platform_device *pdev)
 	if (of_property_read_s32(pdev->dev.of_node, "priority", &priority))
 		priority = 192;
 
-	if (of_property_read_u32(pdev->dev.of_node, "offset", &ctx->offset))
-		if (of_property_read_u32(pdev->dev.of_node, "reg", &ctx->offset))
-			return -EINVAL;
+	ctx->rd = of_device_get_match_data(dev);
+	if (!ctx->rd) {
+		int mask_err, value_err;
 
-	value_err = of_property_read_u32(pdev->dev.of_node, "value", &ctx->value);
-	mask_err = of_property_read_u32(pdev->dev.of_node, "mask", &ctx->mask);
-	if (value_err && mask_err) {
-		dev_err(dev, "unable to read 'value' and 'mask'");
-		return -EINVAL;
-	}
+		if (of_property_read_u32(pdev->dev.of_node, "offset",
+					 &ctx->catchall.offset) &&
+		    of_property_read_u32(pdev->dev.of_node, "reg",
+					 &ctx->catchall.offset))
+			return -EINVAL;
 
-	if (value_err) {
-		/* support old binding */
-		ctx->value = ctx->mask;
-		ctx->mask = 0xFFFFFFFF;
-	} else if (mask_err) {
-		/* support value without mask*/
-		ctx->mask = 0xFFFFFFFF;
+		value_err = of_property_read_u32(pdev->dev.of_node, "value",
+						 &ctx->catchall.value);
+		mask_err = of_property_read_u32(pdev->dev.of_node, "mask",
+						&ctx->catchall.mask);
+		if (value_err && mask_err) {
+			dev_err(dev, "unable to read 'value' and 'mask'");
+			return -EINVAL;
+		}
+
+		if (value_err) {
+			/* support old binding */
+			ctx->catchall.value = ctx->catchall.mask;
+			ctx->catchall.mask = 0xFFFFFFFF;
+		} else if (mask_err) {
+			/* support value without mask */
+			ctx->catchall.mask = 0xFFFFFFFF;
+		}
 	}
 
 	ctx->restart_handler.notifier_call = syscon_restart_handle;
@@ -89,7 +122,30 @@ static int syscon_reboot_probe(struct platform_device *pdev)
 	return err;
 }
 
+static const struct reboot_data gs101_reboot_data = {
+	.mode_bits = {
+		[REBOOT_WARM] = {
+			.offset = 0x3a00, /* SYSTEM_CONFIGURATION */
+			.mask = 0x00000002, /* SWRESET_SYSTEM */
+			.value = 0x00000002,
+			.valid = true,
+		},
+		[REBOOT_SOFT] = {
+			.offset = 0x3a00, /* SYSTEM_CONFIGURATION */
+			.mask = 0x00000002, /* SWRESET_SYSTEM */
+			.value = 0x00000002,
+			.valid = true,
+		},
+	},
+	.catchall = {
+		.offset = 0x3e9c, /* PAD_CTRL_PWR_HOLD */
+		.mask = 0x00000100,
+		.value = 0x00000000,
+	},
+};
+
 static const struct of_device_id syscon_reboot_of_match[] = {
+	{ .compatible = "google,gs101-reboot", .data = &gs101_reboot_data  },
 	{ .compatible = "syscon-reboot" },
 	{}
 };