Date:   Tue, 19 Jan 2021 15:12:50 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     gregkh@...uxfoundation.org
Cc:     linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        jhugo@...eaurora.org, bbhatt@...eaurora.org,
        loic.poulain@...aro.org, netdev@...r.kernel.org,
        hemantk@...eaurora.org
Subject: Re: [RESEND PATCH v18 0/3] userspace MHI client interface driver

Hi Greg,

On Wed, Jan 13, 2021 at 08:56:25PM +0530, Manivannan Sadhasivam wrote:
> Hi Greg,
> 
> On Wed, Jan 06, 2021 at 10:44:13AM -0800, 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
> > https://www.freedesktop.org/wiki/Software/libqmi/ for additional information
> > on libqmi.
> > 
> > Patch is tested using arm64 and x86 based platform.
> > 
> 
> This series looks good to me and I'd like to merge it into mhi-next. You
> shared your reviews on the previous revisions, so I'd like to get your
> opinion first.
> 

Ping!

Thanks,
Mani

> Thanks,
> Mani
> 
> > V18:
> > - Updated commit text for UCI to clarify why this driver is required for QMI
> >   over MHI. Also updated cover letter with same information.
> > 
> > v17:
> > - Updated commit text for UCI driver by mentioning about libqmi open-source
> >   userspace program that will be talking to this UCI kernel driver.
> > - UCI driver depends upon patch "bus: mhi: core: Add helper API to return number
> >   of free TREs".
> > 
> > v16:
> > - Removed reference of WLAN as an external MHI device in documentation and
> >   cover letter.
> > 
> > v15:
> > - Updated documentation related to poll and release operations.
> > 
> > V14:
> > - Fixed device file node format to /dev/<mhi_dev_name> instead of
> >   /dev/mhi_<mhi_dev_name> because "mhi" is already part of mhi device name.
> >   For example old format: /dev/mhi_mhi0_QMI new format: /dev/mhi0_QMI.
> > - Updated MHI documentation to reflect index mhi controller name in
> >   QMI usage example.
> > 
> > V13:
> > - Removed LOOPBACK channel from mhi_device_id table from this patch series.
> >   Pushing a new patch series to add support for LOOPBACK channel and the user
> >   space test application. Also removed the description from kernel documentation.
> > - Added QMI channel to mhi_device_id table. QMI channel has existing libqmi
> >   support from user space.
> > - Updated kernel Documentation for QMI channel and provided external reference
> >   for libqmi.
> > - Updated device file node name by appending mhi device name only, which already
> >   includes mhi controller device name.
> > 
> > V12:
> > - Added loopback test driver under selftest/drivers/mhi. Updated kernel
> >   documentation for the usage of the loopback test application.
> > - Addressed review comments for renaming variable names, updated inline
> >   comments and removed two redundant dev_dbg.
> > 
> > V11:
> > - Fixed review comments for UCI documentation by expanding TLAs and rewording
> >   some sentences.
> > 
> > V10:
> > - Replaced mutex_lock with mutex_lock_interruptible in read() and write() file
> >   ops call back.
> > 
> > V9:
> > - Renamed dl_lock to dl_pending _lock and pending list to dl_pending for
> >   clarity.
> > - Used read lock to protect cur_buf.
> > - Change transfer status check logic and only consider 0 and -EOVERFLOW as
> >   only success.
> > - Added __int to module init function.
> > - Print channel name instead of minor number upon successful probe.
> > 
> > V8:
> > - Fixed kernel test robot compilation error by changing %lu to %zu for
> >   size_t.
> > - Replaced uci with UCI in Kconfig, commit text, and comments in driver
> >   code.
> > - Fixed minor style related comments.
> > 
> > V7:
> > - Decoupled uci device and uci channel objects. uci device is
> >   associated with device file node. uci channel is associated
> >   with MHI channels. uci device refers to uci channel to perform
> >   MHI channel operations for device file operations like read()
> >   and write(). uci device increments its reference count for
> >   every open(). uci device calls mhi_uci_dev_start_chan() to start
> >   the MHI channel. uci channel object is tracking number of times
> >   MHI channel is referred. This allows to keep the MHI channel in
> >   start state until last release() is called. After that uci channel
> >   reference count goes to 0 and uci channel clean up is performed
> >   which stops the MHI channel. After the last call to release() if
> >   driver is removed uci reference count becomes 0 and uci object is
> >   cleaned up.
> > - Use separate uci channel read and write lock to fine grain locking
> >   between reader and writer.
> > - Use uci device lock to synchronize open, release and driver remove.
> > - Optimize for downlink only or uplink only UCI device.
> > 
> > V6:
> > - Moved uci.c to mhi directory.
> > - Updated Kconfig to add module information.
> > - Updated Makefile to rename uci object file name as mhi_uci
> > - Removed kref for open count
> > 
> > V5:
> > - Removed mhi_uci_drv structure.
> > - Used idr instead of creating global list of uci devices.
> > - Used kref instead of local ref counting for uci device and
> >   open count.
> > - Removed unlikely macro.
> > 
> > V4:
> > - Fix locking to protect proper struct members.
> > - Updated documentation describing uci client driver use cases.
> > - Fixed uci ref counting in mhi_uci_open for error case.
> > - Addressed style related review comments.
> > 
> > V3: Added documentation for MHI UCI driver.
> > 
> > V2:
> > - Added mutex lock to prevent multiple readers to access same
> > - mhi buffer which can result into use after free.
> > 
> > Hemant Kumar (3):
> >   bus: mhi: core: Move MHI_MAX_MTU to external header file
> >   docs: Add documentation for userspace client interface
> >   bus: mhi: Add userspace client interface driver
> > 
> >  Documentation/mhi/index.rst     |   1 +
> >  Documentation/mhi/uci.rst       |  95 ++++++
> >  drivers/bus/mhi/Kconfig         |  13 +
> >  drivers/bus/mhi/Makefile        |   3 +
> >  drivers/bus/mhi/core/internal.h |   1 -
> >  drivers/bus/mhi/uci.c           | 664 ++++++++++++++++++++++++++++++++++++++++
> >  include/linux/mhi.h             |   3 +
> >  7 files changed, 779 insertions(+), 1 deletion(-)
> >  create mode 100644 Documentation/mhi/uci.rst
> >  create mode 100644 drivers/bus/mhi/uci.c
> > 
> > -- 
> > The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> > a Linux Foundation Collaborative Project
> > 

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