linux-kernel - Re: [PATCH v2] usb: misc: qcom_eud: Access EUD_MODE

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Message-ID: <2025062812-passive-untracked-1231@gregkh>
Date: Sat, 28 Jun 2025 16:36:04 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Komal Bajaj <komal.bajaj@....qualcomm.com>
Cc: linux-arm-msm@...r.kernel.org, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Souradeep Chowdhury <quic_schowdhu@...cinc.com>,
	Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Subject: Re: [PATCH v2] usb: misc: qcom_eud: Access EUD_MODE_MANAGER2 through
 secure calls

On Fri, Jun 27, 2025 at 06:21:31PM +0530, Komal Bajaj wrote:
> 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@...cinc.com>
> Signed-off-by: Komal Bajaj <komal.bajaj@....qualcomm.com>
> Reviewed-by: Konrad Dybcio <konrad.dybcio@....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>

Why the blank line before this #include line?

> +
>  #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;

So the previous writes are ok, but this one could fail?  And if it does
fail, what did the previous writes cause to happen to the chip / system?

>  	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);

No error checking needed?


>  }
>  
>  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;

-ENOMEM perhaps?

thanks,

greg k-h