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Subject[PATCH v4 2/3] firmware: qcom: scm: Expose download-mode control
Date
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 <sboyd@codeaurora.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
---

Changes since v3:
- Offset register in TCSR
- Spelling

Changes since v2:
- Define memory address by reference to TCSR
- Provide Kconfig option for defaulting to enabled
- Provided some comment in the code

Changes since v1:
- Specify DT propert being two-cell
- Correct handling of scm-call return code

.../devicetree/bindings/firmware/qcom,scm.txt | 2 +
drivers/firmware/Kconfig | 11 ++++
drivers/firmware/qcom_scm-32.c | 6 ++
drivers/firmware/qcom_scm-64.c | 13 ++++
drivers/firmware/qcom_scm.c | 75 ++++++++++++++++++++++
drivers/firmware/qcom_scm.h | 2 +
6 files changed, 109 insertions(+)

diff --git a/Documentation/devicetree/bindings/firmware/qcom,scm.txt b/Documentation/devicetree/bindings/firmware/qcom,scm.txt
index 20f26fbce875..7b40054be0d8 100644
--- a/Documentation/devicetree/bindings/firmware/qcom,scm.txt
+++ b/Documentation/devicetree/bindings/firmware/qcom,scm.txt
@@ -18,6 +18,8 @@ Required properties:
* 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:

diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
index 6e4ed5a9c6fd..fa87a055905e 100644
--- a/drivers/firmware/Kconfig
+++ b/drivers/firmware/Kconfig
@@ -215,6 +215,17 @@ config QCOM_SCM_64
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
diff --git a/drivers/firmware/qcom_scm-32.c b/drivers/firmware/qcom_scm-32.c
index 11fdb1584823..68b2033bc30e 100644
--- a/drivers/firmware/qcom_scm-32.c
+++ b/drivers/firmware/qcom_scm-32.c
@@ -561,6 +561,12 @@ int __qcom_scm_pas_mss_reset(struct device *dev, bool reset)
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 {
diff --git a/drivers/firmware/qcom_scm-64.c b/drivers/firmware/qcom_scm-64.c
index bf50fb59852e..3fea6f563ca9 100644
--- a/drivers/firmware/qcom_scm-64.c
+++ b/drivers/firmware/qcom_scm-64.c
@@ -440,6 +440,19 @@ int __qcom_scm_iommu_secure_ptbl_init(struct device *dev, u64 addr, u32 size,
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)
{
diff --git a/drivers/firmware/qcom_scm.c b/drivers/firmware/qcom_scm.c
index e18d63935648..9064e559a01f 100644
--- a/drivers/firmware/qcom_scm.c
+++ b/drivers/firmware/qcom_scm.c
@@ -19,15 +19,20 @@
#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)
#define SCM_HAS_BUS_CLK BIT(2)
@@ -38,6 +43,8 @@ struct qcom_scm {
struct clk *iface_clk;
struct clk *bus_clk;
struct reset_controller_dev reset;
+
+ u64 dload_mode_addr;
};

static struct qcom_scm *__scm;
@@ -345,6 +352,54 @@ int qcom_scm_io_writel(phys_addr_t addr, unsigned int val)
}
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
*/
@@ -370,6 +425,10 @@ static int qcom_scm_probe(struct platform_device *pdev)
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) {
scm->core_clk = devm_clk_get(&pdev->dev, "core");
@@ -418,9 +477,24 @@ static int qcom_scm_probe(struct platform_device *pdev)

__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[] = {
{ .compatible = "qcom,scm-apq8064",
/* FIXME: This should have .data = (void *) SCM_HAS_CORE_CLK */
@@ -448,6 +522,7 @@ static struct platform_driver qcom_scm_driver = {
.of_match_table = qcom_scm_dt_match,
},
.probe = qcom_scm_probe,
+ .shutdown = qcom_scm_shutdown,
};

static int __init qcom_scm_init(void)
diff --git a/drivers/firmware/qcom_scm.h b/drivers/firmware/qcom_scm.h
index a60e4b9b1394..83f171c23943 100644
--- a/drivers/firmware/qcom_scm.h
+++ b/drivers/firmware/qcom_scm.h
@@ -14,9 +14,11 @@

#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
--
2.12.0
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