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Date:   Wed, 3 Feb 2021 10:40:28 -0800
From:   Jakub Kicinski <kuba@kernel.org>
To:     Loic Poulain <loic.poulain@linaro.org>
Cc:     Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>,
        Greg KH <gregkh@linuxfoundation.org>,
        David Miller <davem@davemloft.net>,
        linux-arm-msm <linux-arm-msm@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>,
        Jeffrey Hugo <jhugo@codeaurora.org>,
        Bhaumik Bhatt <bbhatt@codeaurora.org>,
        Network Development <netdev@vger.kernel.org>
Subject: Re: [RESEND PATCH v18 0/3] userspace MHI client interface driver
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On Wed, 3 Feb 2021 19:28:28 +0100 Loic Poulain wrote:
> On Wed, 3 Feb 2021 at 19:05, Jakub Kicinski <kuba@kernel.org> wrote:
> > On Wed, 03 Feb 2021 09:45:06 +0530 Manivannan Sadhasivam wrote:  
> > > The current patchset only supports QMI channel so I'd request you to
> > > review the chardev node created for it. The QMI chardev node created
> > > will be unique for the MHI bus and the number of nodes depends on the
> > > MHI controllers in the system (typically 1 but not limited).  
> >
> > If you want to add a MHI QMI driver, please write a QMI-only driver.
> > This generic "userspace client interface" driver is a no go. Nobody will
> > have the time and attention to police what you throw in there later.  
> 
> Think it should be seen as filtered userspace access to MHI bus
> (filtered because not all channels are exposed), again it's not
> specific to MHI, any bus in Linux offers that (i2c, spi, usb, serial,
> etc...). It will not be specific to QMI, since we will also need it
> for MBIM (modem control path), AT commands, and GPS (NMEA frames), all
> these protocols are usually handled by userspace tools and not linked
> to any internal Linux framework, so it would be better not having a
> dedicated chardev for each of them.

The more people argue for this backdoor interface the more distrustful
of it we'll become. Keep going at your own peril.