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

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Message-ID: <2025070843-strangely-unplanted-3ef5@gregkh>
Date: Tue, 8 Jul 2025 10:01:26 +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 Tue, Jul 08, 2025 at 11:23:56AM +0530, Komal Bajaj wrote:
> 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

No need for this, it's pretty obvious this is the case when all in one
long list.

thanks,

greg k-h