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Date:   Wed, 16 Dec 2020 10:42:17 +0100
From:   Greg Kroah-Hartman <>
To:     Loic Poulain <>
Cc:     Manivannan Sadhasivam <>,
        Jakub Kicinski <>,
        linux-arm-msm <>,
        Hemant Kumar <>,
        open list <>,
        Jeffrey Hugo <>,
        Bhaumik Bhatt <>,
        Network Development <>
Subject: Re: [PATCH v18 0/3] userspace MHI client interface driver

On Wed, Dec 16, 2020 at 10:17:30AM +0100, Loic Poulain wrote:
> Hi Folks,
> On Fri, 11 Dec 2020 at 20:45, Hemant Kumar <> wrote:
> >
> > This patch series adds support for UCI driver. UCI driver enables userspace
> > clients to communicate to external MHI devices like modem. UCI driver probe
> > creates standard character device file nodes for userspace clients to
> > perform open, read, write, poll and release file operations. These file
> > operations call MHI core layer APIs to perform data transfer using MHI bus
> > to communicate with MHI device.
> >
> > This interface allows exposing modem control channel(s) such as QMI, MBIM,
> > or AT commands to userspace which can be used to configure the modem using
> > tools such as libqmi, ModemManager, minicom (for AT), etc over MHI. This is
> > required as there are no kernel APIs to access modem control path for device
> > configuration. Data path transporting the network payload (IP), however, is
> > routed to the Linux network via the mhi-net driver. Currently driver supports
> > QMI channel. libqmi is userspace MHI client which communicates to a QMI
> > service using QMI channel. Please refer to
> > for additional information
> > on libqmi.
> >
> > Patch is tested using arm64 and x86 based platform.
> Are there any blockers or unadressed comments remaining on this
> series? As far as I understand, the original blocker was the net/WiFi
> mention in the commit message, that caused a legitimate concern from
> network maintainer. It has been clarified now that this driver is not
> for exposing any channel that could be otherwise handled properly by
> an existing Linux subsystem/interface. It will be especially used as a
> pipe for modem QMI channel (or AT commands) in the same way as the USB
> CDC-WDM driver is doing (keeping userspace compatibility). Other MHI
> channels, such as network data, QRTR, etc are not exposed and
> correctly bound to the corresponding Linux subsystems.
> The correlated worry was that it could be a userspace channel facility
> for 'everything qualcomm', but we could say the same for other
> existing busses with userspace shunt (/dev/bus/usb, /dev/i2c,
> /dev/spidev, PCI UIO, UART...). Moreover, it is mitigated by the fact
> that not all MHI channels are exposed by default, but only the allowed
> ones (QMI in the initial version). For sure, special care must be
> given to any further channel addition.

It's the middle of the merge window, we can't do anything with new
patches at all until 5.11-rc1 is out, so please be patient.


greg k-h

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