[PATCH v2] usb: misc: qcom_eud: Access EUD_MODE_MANAGER2 through secure calls

[Komal Bajaj <komal.bajaj@oss.qualcomm.com>]

EUD_MODE_MANAGER2 register is mapped to a memory region that is marked
as read-only for HLOS, enforcing access restrictions that prohibit
direct memory-mapped writes via writel().

Attempts to write to this region from HLOS can result in silent failures
or memory access violations, particularly when toggling EUD (Embedded
USB Debugger) state. To ensure secure register access, modify the driver
to use qcom_scm_io_writel(), which routes the write operation to Qualcomm
Secure Channel Monitor (SCM). SCM has the necessary permissions to access
protected memory regions, enabling reliable control over EUD state.

SC7280, the only user of EUD is also affected, indicating that this could
never have worked on a properly fused device.

Fixes: 9a1bf58ccd44 ("usb: misc: eud: Add driver support for Embedded USB Debugger(EUD)")
Signed-off-by: Melody Olvera <quic_molvera@quicinc.com>
Signed-off-by: Komal Bajaj <komal.bajaj@oss.qualcomm.com>
Reviewed-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
---
Changes in v2:
* Drop separate compatible to be added for secure eud
* Use secure call to access EUD mode manager register
* Link to v1: https://lore.kernel.org/all/20240807183205.803847-1-quic_molvera@quicinc.com/

 drivers/usb/misc/qcom_eud.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/drivers/usb/misc/qcom_eud.c b/drivers/usb/misc/qcom_eud.c
index 83079c414b4f..30c999c49eb0 100644
--- a/drivers/usb/misc/qcom_eud.c
+++ b/drivers/usb/misc/qcom_eud.c
@@ -16,6 +16,8 @@
 #include <linux/sysfs.h>
 #include <linux/usb/role.h>
 
+#include <linux/firmware/qcom/qcom_scm.h>
+
 #define EUD_REG_INT1_EN_MASK	0x0024
 #define EUD_REG_INT_STATUS_1	0x0044
 #define EUD_REG_CTL_OUT_1	0x0074
@@ -34,7 +36,7 @@ struct eud_chip {
 	struct device			*dev;
 	struct usb_role_switch		*role_sw;
 	void __iomem			*base;
-	void __iomem			*mode_mgr;
+	phys_addr_t			mode_mgr;
 	unsigned int			int_status;
 	int				irq;
 	bool				enabled;
@@ -43,10 +45,14 @@ struct eud_chip {
 
 static int enable_eud(struct eud_chip *priv)
 {
+	int ret;
+
 	writel(EUD_ENABLE, priv->base + EUD_REG_CSR_EUD_EN);
 	writel(EUD_INT_VBUS | EUD_INT_SAFE_MODE,
 			priv->base + EUD_REG_INT1_EN_MASK);
-	writel(1, priv->mode_mgr + EUD_REG_EUD_EN2);
+	ret = qcom_scm_io_writel(priv->mode_mgr + EUD_REG_EUD_EN2, 1);
+	if (ret)
+		return ret;
 
 	return usb_role_switch_set_role(priv->role_sw, USB_ROLE_DEVICE);
 }
@@ -54,7 +60,7 @@ static int enable_eud(struct eud_chip *priv)
 static void disable_eud(struct eud_chip *priv)
 {
 	writel(0, priv->base + EUD_REG_CSR_EUD_EN);
-	writel(0, priv->mode_mgr + EUD_REG_EUD_EN2);
+	qcom_scm_io_writel(priv->mode_mgr + EUD_REG_EUD_EN2, 0);
 }
 
 static ssize_t enable_show(struct device *dev,
@@ -178,6 +184,7 @@ static void eud_role_switch_release(void *data)
 static int eud_probe(struct platform_device *pdev)
 {
 	struct eud_chip *chip;
+	struct resource *res;
 	int ret;
 
 	chip = devm_kzalloc(&pdev->dev, sizeof(*chip), GFP_KERNEL);
@@ -200,9 +207,10 @@ static int eud_probe(struct platform_device *pdev)
 	if (IS_ERR(chip->base))
 		return PTR_ERR(chip->base);
 
-	chip->mode_mgr = devm_platform_ioremap_resource(pdev, 1);
-	if (IS_ERR(chip->mode_mgr))
-		return PTR_ERR(chip->mode_mgr);
+	res = platform_get_resource(pdev, IORESOURCE_MEM, 1);
+	if (!res)
+		return -ENODEV;
+	chip->mode_mgr = res->start;
 
 	chip->irq = platform_get_irq(pdev, 0);
 	if (chip->irq < 0)
-- 
2.48.1