[PATCH 3/4] firmware: qcom: scm: Add minidump SRAM support

[Mukesh Ojha]

On most Qualcomm SoCs where minidump is supported, a word in always-on
SRAM is shared between the kernel and boot firmware. Before DDR is
initialised on the warm reset following a crash, firmware reads this
word to decide if minidump is enabled and collect a minidump and where
to deliver it (USB upload to a host, or save to local storage).

The SRAM region is described by a 'sram'/'sram-names' phandle pair on
the SCM DT node. If the property is absent the feature is silently
disabled, keeping existing SoCs unaffected.

Expose a 'minidump_dest' module parameter (default: usb) so the user can
select the destination. Only the string names "usb" or "storage" are
accepted; an invalid value is rejected with -EINVAL. Changing the
destination while minidump mode is already active updates SRAM immediately.

Suggested-by: Konrad Dybcio <konrad.dybcio@xxxxxxxxxxxxxxxx>
Signed-off-by: Mukesh Ojha <mukesh.ojha@xxxxxxxxxxxxxxxx>
---
 drivers/firmware/qcom/qcom_scm.c | 95 ++++++++++++++++++++++++++++++++
 1 file changed, 95 insertions(+)

diff --git a/drivers/firmware/qcom/qcom_scm.c b/drivers/firmware/qcom/qcom_scm.c
index f65b132004a5..b57f8cce7a8c 100644
--- a/drivers/firmware/qcom/qcom_scm.c
+++ b/drivers/firmware/qcom/qcom_scm.c
@@ -57,6 +57,7 @@ struct qcom_scm {
 	int scm_vote_count;
 
 	u64 dload_mode_addr;
+	void __iomem *minidump_sram;
 
 	struct qcom_tzmem_pool *mempool;
 	unsigned int wq_cnt;
@@ -141,6 +142,18 @@ static const u8 qcom_scm_cpu_warm_bits[QCOM_SCM_BOOT_MAX_CPUS] = {
 #define QCOM_DLOAD_MINIDUMP	2
 #define QCOM_DLOAD_BOTHDUMP	3
 
+/* Minidump destination values written to always-on SRAM for boot firmware */
+#define QCOM_MINIDUMP_DEST_USB		0x0
+#define QCOM_MINIDUMP_DEST_STORAGE	0x2
+
+static u32 minidump_dest = QCOM_MINIDUMP_DEST_USB;
+
+static const char * const minidump_dest_name[] = { "usb", "storage" };
+static const u32 minidump_dest_val[] = {
+	QCOM_MINIDUMP_DEST_USB,
+	QCOM_MINIDUMP_DEST_STORAGE,
+};
+
 #define QCOM_SCM_DEFAULT_WAITQ_COUNT 1
 
 static const char * const qcom_scm_convention_names[] = {
@@ -568,6 +581,17 @@ static void qcom_scm_set_download_mode(u32 dload_mode)
 
 	if (ret)
 		dev_err(__scm->dev, "failed to set download mode: %d\n", ret);
+
+	/*
+	 * Mirror the destination into the always-on SRAM so boot firmware
+	 * can read it before DDR is initialised on the next warm reset.
+	 * Only written when minidump is active; skip if SRAM already holds
+	 * the requested destination to avoid unnecessary writes.
+	 */
+	if (__scm->minidump_sram && (dload_mode & QCOM_DLOAD_MINIDUMP)) {
+		if (readl_relaxed(__scm->minidump_sram) != minidump_dest)
+			writel_relaxed(minidump_dest, __scm->minidump_sram);
+	}
 }
 
 /**
@@ -2055,6 +2079,37 @@ int qcom_scm_gpu_init_regs(u32 gpu_req)
 }
 EXPORT_SYMBOL_GPL(qcom_scm_gpu_init_regs);
 
+static int qcom_scm_map_minidump_sram(struct device *dev, void __iomem **out)
+{
+	struct device_node *np = dev->of_node;
+	struct device_node *sram_np;
+	struct resource res;
+	int ret;
+
+	if (of_property_match_string(np, "sram-names", "minidump") < 0)
+		return 0;
+
+	sram_np = of_parse_phandle(np, "sram", 0);
+	if (!sram_np)
+		return -EINVAL;
+
+	ret = of_address_to_resource(sram_np, 0, &res);
+	of_node_put(sram_np);
+	if (ret)
+		return ret;
+
+	if (resource_size(&res) < sizeof(u32)) {
+		dev_err(dev, "minidump SRAM region too small\n");
+		return -EINVAL;
+	}
+
+	*out = devm_ioremap(dev, res.start, resource_size(&res));
+	if (!*out)
+		return -ENOMEM;
+
+	return 0;
+}
+
 static int qcom_scm_find_dload_address(struct device *dev, u64 *addr)
 {
 	struct device_node *tcsr;
@@ -2748,6 +2803,41 @@ static const struct kernel_param_ops download_mode_param_ops = {
 module_param_cb(download_mode, &download_mode_param_ops, NULL, 0644);
 MODULE_PARM_DESC(download_mode, "download mode: off/0/N for no dump mode, full/on/1/Y for full dump mode, mini for minidump mode and full,mini for both full and minidump mode together are acceptable values");
 
+static int get_minidump_dest(char *buffer, const struct kernel_param *kp)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(minidump_dest_val); i++)
+		if (minidump_dest == minidump_dest_val[i])
+			return sysfs_emit(buffer, "%s\n", minidump_dest_name[i]);
+
+	return sysfs_emit(buffer, "unknown\n");
+}
+
+static int set_minidump_dest(const char *val, const struct kernel_param *kp)
+{
+	int i;
+
+	i = sysfs_match_string(minidump_dest_name, val);
+	if (i < 0)
+		return -EINVAL;
+
+	minidump_dest = minidump_dest_val[i];
+	if (__scm && __scm->minidump_sram && (download_mode & QCOM_DLOAD_MINIDUMP) &&
+	    readl_relaxed(__scm->minidump_sram) != minidump_dest)
+		writel_relaxed(minidump_dest, __scm->minidump_sram);
+
+	return 0;
+}
+
+static const struct kernel_param_ops minidump_dest_param_ops = {
+	.get = get_minidump_dest,
+	.set = set_minidump_dest,
+};
+
+module_param_cb(minidump_dest, &minidump_dest_param_ops, NULL, 0644);
+MODULE_PARM_DESC(minidump_dest, "Minidump SRAM destination: usb (default) or storage");
+
 static int qcom_scm_probe(struct platform_device *pdev)
 {
 	struct qcom_tzmem_pool_config pool_config;
@@ -2765,6 +2855,11 @@ static int qcom_scm_probe(struct platform_device *pdev)
 		return dev_err_probe(&pdev->dev, ret,
 				     "Failed to find download mode address\n");
 
+	ret = qcom_scm_map_minidump_sram(&pdev->dev, &scm->minidump_sram);
+	if (ret < 0)
+		return dev_err_probe(&pdev->dev, ret,
+				     "Failed to map minidump SRAM\n");
+
 	mutex_init(&scm->scm_bw_lock);
 
 	scm->path = devm_of_icc_get(&pdev->dev, NULL);
-- 
2.53.0