linux-kernel - Re: [PATCH v7] usb: misc: qcom_eud: Access EUD_MODE

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Message-ID: <3fogucs66bpupdwbzlhevpglxg423ub2vkn6zouakjtswa4tu3@drhgtfvr6tz7>
Date: Wed, 23 Jul 2025 14:08:20 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Komal Bajaj <komal.bajaj@....qualcomm.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Souradeep Chowdhury <quic_schowdhu@...cinc.com>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org,
        Melody Olvera <quic_molvera@...cinc.com>,
        Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Subject: Re: [PATCH v7] usb: misc: qcom_eud: Access EUD_MODE_MANAGER2 through
 secure calls

On Tue, Jul 22, 2025 at 05:01:53PM +0530, Komal Bajaj wrote:
> EUD_MODE_MANAGER2 register is mapped to a memory region that is marked
> as read-only for operating system running at EL1, 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 v7:
> - Updated the commit message as per Greg's comment
> - Link to v6: https://lore.kernel.org/r/20250721-eud_mode_manager_secure_access-v6-1-fe603325ac04@oss.qualcomm.com
> 
> Changes in v6:
> - Propagating the error code from disable_eud(), per Dmitry's suggestion
> - Link to v5: https://lore.kernel.org/r/20250715-eud_mode_manager_secure_access-v5-1-e769be308d4a@oss.qualcomm.com
> 
> usb: misc: qcom_eud: Access EUD_MODE_MANAGER2 through secure calls
> 
> Changes in v5:
> * Changed select QCOM_SCM to depends on QCOM_SCM in Kconfig per Greg's review
> * Link to v4: https://lore.kernel.org/all/20250709065533.25724-1-komal.bajaj@oss.qualcomm.com/
> 
> Changes in v4:
> * Added error logging in disable_eud() for SCM write failures, per Konrad’s suggestion
> * Link to v3: https://lore.kernel.org/all/20250708085208.19089-1-komal.bajaj@oss.qualcomm.com/
> 
> Changes in v3:
> * Moved secure write before normal writes
> * Added error checking in disable_eud()
> * Use ENOMEM error code if platform_get_resource() fails
> * Select QCOM_SCM driver if USB_QCOM_EUD is enabled
> * Link to v2: https://lore.kernel.org/all/20250627125131.27606-1-komal.bajaj@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/Kconfig    |  1 +
>  drivers/usb/misc/qcom_eud.c | 33 ++++++++++++++++++++++++---------
>  2 files changed, 25 insertions(+), 9 deletions(-)
> 

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>


-- 
With best wishes
Dmitry