firmware: qcom: scm: Expose download-mode control

In order to aid post-mortem debugging the Qualcomm platforms provide a
"memory download mode", where the boot loader will provide an interface
for custom tools to "download" the content of RAM to a host machine.

The mode is triggered by writing a magic value somewhere in RAM, that is
read in the boot code path after a warm-restart. Two mechanism for
setting this magic value are supported in modern platforms; a direct SCM
call to enable the mode or through a secure io write of a magic value.

In order for a normal reboot not to trigger "download mode" the magic
must be cleared during a clean reboot.

Download mode has to be enabled by including qcom_scm.download_mode=1 on
the command line.

Reviewed-by: Stephen Boyd <[e-mail]>
Signed-off-by: Bjorn Andersson <[e-mail]>
Signed-off-by: Andy Gross <[e-mail]>

Documentation/devicetree/bindings/firmware/qcom,scm.txt

···
  * Core, iface, and bus clocks required for "qcom,scm"
 - clock-names: Must contain "core" for the core clock, "iface" for the interface
   clock and "bus" for the bus clock per the requirements of the compatible.
+- qcom,dload-mode: phandle to the TCSR hardware block and offset of the
+		   download mode control register (optional)
 
 Example for MSM8916:
 

drivers/firmware/Kconfig

···
 	def_bool y
 	depends on QCOM_SCM && ARM64
 
+config QCOM_SCM_DOWNLOAD_MODE_DEFAULT
+	bool "Qualcomm download mode enabled by default"
+	depends on QCOM_SCM
+	help
+	  A device with "download mode" enabled will upon an unexpected
+	  warm-restart enter a special debug mode that allows the user to
+	  "download" memory content over USB for offline postmortem analysis.
+	  The feature can be enabled/disabled on the kernel command line.
+
+	  Say Y here to enable "download mode" by default.
+
 config TI_SCI_PROTOCOL
 	tristate "TI System Control Interface (TISCI) Message Protocol"
 	depends on TI_MESSAGE_MANAGER

drivers/firmware/qcom_scm-32.c

···
 	return ret ? : le32_to_cpu(out);
 }
 
+int __qcom_scm_set_dload_mode(struct device *dev, bool enable)
+{
+	return qcom_scm_call_atomic2(QCOM_SCM_SVC_BOOT, QCOM_SCM_SET_DLOAD_MODE,
+				     enable ? QCOM_SCM_SET_DLOAD_MODE : 0, 0);
+}
+
 int __qcom_scm_set_remote_state(struct device *dev, u32 state, u32 id)
 {
 	struct {

drivers/firmware/qcom_scm-64.c

···
 	return ret;
 }
 
+int __qcom_scm_set_dload_mode(struct device *dev, bool enable)
+{
+	struct qcom_scm_desc desc = {0};
+	struct arm_smccc_res res;
+
+	desc.args[0] = QCOM_SCM_SET_DLOAD_MODE;
+	desc.args[1] = enable ? QCOM_SCM_SET_DLOAD_MODE : 0;
+	desc.arginfo = QCOM_SCM_ARGS(2);
+
+	return qcom_scm_call(dev, QCOM_SCM_SVC_BOOT, QCOM_SCM_SET_DLOAD_MODE,
+			     &desc, &res);
+}
+
 int __qcom_scm_io_readl(struct device *dev, phys_addr_t addr,
 			unsigned int *val)
 {

drivers/firmware/qcom_scm.c

···
 #include <linux/cpumask.h>
 #include <linux/export.h>
 #include <linux/dma-mapping.h>
+#include <linux/module.h>
 #include <linux/types.h>
 #include <linux/qcom_scm.h>
 #include <linux/of.h>
+#include <linux/of_address.h>
 #include <linux/of_platform.h>
 #include <linux/clk.h>
 #include <linux/reset-controller.h>
 
 #include "qcom_scm.h"
+
+static bool download_mode = IS_ENABLED(CONFIG_QCOM_SCM_DOWNLOAD_MODE_DEFAULT);
+module_param(download_mode, bool, 0);
 
 #define SCM_HAS_CORE_CLK	BIT(0)
 #define SCM_HAS_IFACE_CLK	BIT(1)
···
 	struct clk *iface_clk;
 	struct clk *bus_clk;
 	struct reset_controller_dev reset;
+
+	u64 dload_mode_addr;
 };
 
 static struct qcom_scm *__scm;
···
 }
 EXPORT_SYMBOL(qcom_scm_io_writel);
 
+static void qcom_scm_set_download_mode(bool enable)
+{
+	bool avail;
+	int ret = 0;
+
+	avail = __qcom_scm_is_call_available(__scm->dev,
+					     QCOM_SCM_SVC_BOOT,
+					     QCOM_SCM_SET_DLOAD_MODE);
+	if (avail) {
+		ret = __qcom_scm_set_dload_mode(__scm->dev, enable);
+	} else if (__scm->dload_mode_addr) {
+		ret = __qcom_scm_io_writel(__scm->dev, __scm->dload_mode_addr,
+					   enable ? QCOM_SCM_SET_DLOAD_MODE : 0);
+	} else {
+		dev_err(__scm->dev,
+			"No available mechanism for setting download mode\n");
+	}
+
+	if (ret)
+		dev_err(__scm->dev, "failed to set download mode: %d\n", ret);
+}
+
+static int qcom_scm_find_dload_address(struct device *dev, u64 *addr)
+{
+	struct device_node *tcsr;
+	struct device_node *np = dev->of_node;
+	struct resource res;
+	u32 offset;
+	int ret;
+
+	tcsr = of_parse_phandle(np, "qcom,dload-mode", 0);
+	if (!tcsr)
+		return 0;
+
+	ret = of_address_to_resource(tcsr, 0, &res);
+	of_node_put(tcsr);
+	if (ret)
+		return ret;
+
+	ret = of_property_read_u32_index(np, "qcom,dload-mode", 1, &offset);
+	if (ret < 0)
+		return ret;
+
+	*addr = res.start + offset;
+
+	return 0;
+}
+
 /**
  * qcom_scm_is_available() - Checks if SCM is available
  */
···
 	scm = devm_kzalloc(&pdev->dev, sizeof(*scm), GFP_KERNEL);
 	if (!scm)
 		return -ENOMEM;
+
+	ret = qcom_scm_find_dload_address(&pdev->dev, &scm->dload_mode_addr);
+	if (ret < 0)
+		return ret;
 
 	clks = (unsigned long)of_device_get_match_data(&pdev->dev);
 	if (clks & SCM_HAS_CORE_CLK) {
···
 
 	__qcom_scm_init();
 
+	/*
+	 * If requested enable "download mode", from this point on warmboot
+	 * will cause the the boot stages to enter download mode, unless
+	 * disabled below by a clean shutdown/reboot.
+	 */
+	if (download_mode)
+		qcom_scm_set_download_mode(true);
+
 	return 0;
+}
+
+static void qcom_scm_shutdown(struct platform_device *pdev)
+{
+	/* Clean shutdown, disable download mode to allow normal restart */
+	if (download_mode)
+		qcom_scm_set_download_mode(false);
 }
 
 static const struct of_device_id qcom_scm_dt_match[] = {
···
 		.of_match_table = qcom_scm_dt_match,
 	},
 	.probe = qcom_scm_probe,
+	.shutdown = qcom_scm_shutdown,
 };
 
 static int __init qcom_scm_init(void)

drivers/firmware/qcom_scm.h

···
 
 #define QCOM_SCM_SVC_BOOT		0x1
 #define QCOM_SCM_BOOT_ADDR		0x1
+#define QCOM_SCM_SET_DLOAD_MODE		0x10
 #define QCOM_SCM_BOOT_ADDR_MC		0x11
 #define QCOM_SCM_SET_REMOTE_STATE	0xa
 extern int __qcom_scm_set_remote_state(struct device *dev, u32 state, u32 id);
+extern int __qcom_scm_set_dload_mode(struct device *dev, bool enable);
 
 #define QCOM_SCM_FLAG_HLOS		0x01
 #define QCOM_SCM_FLAG_COLDBOOT_MC	0x02