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

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Message-ID: <CAPHGfUOUR=m2rq-rFbUbWjF93qwY5ikHc+M0_KuHOut86z+Mqg@mail.gmail.com>
Date: Tue, 8 Jul 2025 11:23:56 +0530
From: Komal Bajaj <komal.bajaj@....qualcomm.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
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 Sat, Jun 28, 2025 at 8:06 PM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> 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?

The qcom_scm.h header has been placed in a distinct paragraph to clearly
differentiate it from generic subsystem headers, with a blank line included
for visual distinction

>
> > +
> >  #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?

Thanks for pointing that out. I will move the SCM write before the direct
register writes to avoid any inconsistent state if the SCM call fails

>
> >       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?

ACK

>
>
> >  }
> >
> >  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?

ACK

>
> thanks,
>
> greg k-h