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

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Message-ID: <b7mv4u2parcyzrm67yufuor3cwx265kaoae23rksbbuu4aaayl@7a6xxfmganof>
Date: Sat, 28 Jun 2025 08:44:30 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Komal Bajaj <komal.bajaj@....qualcomm.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        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.

Most likely SC7280 Chrome platforms were fused differently or used a
different configuration of the TZ.

The question is whether there can be other platforms (e.g. SC7180 Chrome
or SDM845 Cheeza prototypes) which should use direct register access
instead of going through the SCM.

> 
> 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(-)
> 

-- 
With best wishes
Dmitry