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Subject: Re: [PATCH] i2c: virtio: Add support for zero-length requests
To:     Viresh Kumar <viresh.kumar@linaro.org>,
        Wolfram Sang <wsa@kernel.org>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Jason Wang <jasowang@redhat.com>
Cc:     Vincent Guittot <vincent.guittot@linaro.org>,
        Arnd Bergmann <arnd@kernel.org>,
        stratos-dev@op-lists.linaro.org,
        =?UTF-8?Q?Alex_Benn=c3=a9e?= <alex.bennee@linaro.org>,
        cohuck@redhat.com,
        Vincent Whitchurch <vincent.whitchurch@axis.com>,
        linux-i2c@vger.kernel.org,
        virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org, conghui.chen@intel.com
References: <7c58868cd26d2fc4bd82d0d8b0dfb55636380110.1634808714.git.viresh.kumar@linaro.org>
From:   Jie Deng <jie.deng@intel.com>
Message-ID: <0adf1c36-a00b-f16f-e631-439148c4f956@intel.com>
Date:   Fri, 22 Oct 2021 14:51:10 +0800
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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@linaro.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@intel.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 ?