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From:   Arnd Bergmann <arnd@kernel.org>
Date:   Fri, 22 Oct 2021 09:08:54 +0200
Message-ID: <CAK8P3a1Zt-4goCHWEWcEqwDVwHYp_T=w3rX5pf81Jz_818=Nkw@mail.gmail.com>
Subject: Re: [PATCH] i2c: virtio: Add support for zero-length requests
To:     Viresh Kumar <viresh.kumar@linaro.org>
Cc:     Jie Deng <jie.deng@intel.com>, Wolfram Sang <wsa@kernel.org>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Jason Wang <jasowang@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Stratos Mailing List <stratos-dev@op-lists.linaro.org>,
        =?UTF-8?B?QWxleCBCZW5uw6ll?= <alex.bennee@linaro.org>,
        Cornelia Huck <cohuck@redhat.com>,
        Vincent Whitchurch <vincent.whitchurch@axis.com>,
        Linux I2C <linux-i2c@vger.kernel.org>,
        "open list:DRM DRIVER FOR QEMU'S CIRRUS DEVICE" 
        <virtualization@lists.linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        conghui.chen@intel.com
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On Fri, Oct 22, 2021 at 8:58 AM Viresh Kumar <viresh.kumar@linaro.org> wrote:
> On 22-10-21, 14:51, Jie Deng wrote:
> > > +   if (!virtio_has_feature(vdev, VIRTIO_I2C_F_ZERO_LENGTH_REQUEST)) {
> > > +           dev_err(&vdev->dev, "Zero-length request feature is mandatory\n");
> > > +           return -EINVAL;
> >
> >
> > It might be better to return -EOPNOTSUPP ?
>
> Maybe that or one of these:
>
> #define EBADE           52      /* Invalid exchange */
> #define EPROTO          71      /* Protocol error */
> #define EPFNOSUPPORT    96      /* Protocol family not supported */
> #define ECONNREFUSED    111     /* Connection refused */
>
> Arnd, any suggestions ? This is about the mandatory feature not being offered by
> the device.

These are mostly used for network operations, I'd stick with either EINVAL
or ENXIO in this case.

        Arnd