linux-kernel - Re: [PATCH] i2c: virtio: Add support for zero-length requests

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Date:   Fri, 22 Oct 2021 05:03:36 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jie Deng <jie.deng@...el.com>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        Wolfram Sang <wsa@...nel.org>,
        Jason Wang <jasowang@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Arnd Bergmann <arnd@...nel.org>,
        stratos-dev@...lists.linaro.org,
        Alex Bennée <alex.bennee@...aro.org>,
        cohuck@...hat.com,
        Vincent Whitchurch <vincent.whitchurch@...s.com>,
        linux-i2c@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, conghui.chen@...el.com
Subject: Re: [PATCH] i2c: virtio: Add support for zero-length requests

On Fri, Oct 22, 2021 at 02:51:10PM +0800, Jie Deng wrote:
> 
> On 2021/10/21 17:47, Viresh Kumar wrote:
> > The virtio specification received a new mandatory feature
> > (VIRTIO_I2C_F_ZERO_LENGTH_REQUEST) for zero length requests. Fail if the
> > feature isn't offered by the device.
> > 
> > For each read-request, set the VIRTIO_I2C_FLAGS_M_RD flag, as required
> > by the VIRTIO_I2C_F_ZERO_LENGTH_REQUEST feature.
> > 
> > This allows us to support zero length requests, like SMBUS Quick, where
> > the buffer need not be sent anymore.
> > 
> > Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> > ---
> > Hi Wolfram,
> > 
> > Please do not apply this until the spec changes [1] are merged, sending it early
> > to get review done. I will ping you later once the spec is merged.
> > 
> > [1] https://lists.oasis-open.org/archives/virtio-dev/202110/msg00109.html
> > 
> >   drivers/i2c/busses/i2c-virtio.c | 56 ++++++++++++++++++---------------
> >   include/uapi/linux/virtio_i2c.h |  6 ++++
> >   2 files changed, 36 insertions(+), 26 deletions(-)
> > 
> 
> Acked-by: Jie Deng<jie.deng@...el.com>  once the spec is merged.


There's supposed to be space before < btw. and one puts # before any
comments this way tools can process the ack automatically:

Acked-by: Jie Deng<jie.deng@...el.com> # once the spec is merged.

> 
> 
> > +	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 ?
>