linux-kernel - Re: [PATCH v11] i2c: virtio: add a virtio i2c frontend driver

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Date:   Thu, 1 Jul 2021 11:48:46 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Jie Deng <jie.deng@...el.com>
Cc:     linux-i2c@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, wsa@...nel.org,
        wsa+renesas@...g-engineering.com, mst@...hat.com, arnd@...db.de,
        jasowang@...hat.com, andriy.shevchenko@...ux.intel.com,
        yu1.wang@...el.com, shuo.a.liu@...el.com, conghui.chen@...el.com,
        stefanha@...hat.com
Subject: Re: [PATCH v11] i2c: virtio: add a virtio i2c frontend driver

On 01-07-21, 14:10, Jie Deng wrote:
> I think a fixed number of sgs will make things easier to develop backend.

Yeah, but it looks awkward to send a message buffer which isn't used
at all. From protocol's point of view, it just looks wrong/buggy.

The backend can just look at the number of elements received, they
can either be 2 (in case of zero-length) transfer, or 3 (for
read/write) and any other number is invalid.

> If you prefer to parse the number of descriptors instead of using the msg
> length to
> 
> distinguish the zero-length request from other requests, I'm OK to set a
> limit.

My concern is more about the specification here first.

> if (!msgs[i].len) {
>     sg_init_one(&msg_buf, reqs[i].buf, msgs[i].len);
> 
>     if (msgs[i].flags & I2C_M_RD)
>         sgs[outcnt + incnt++] = &msg_buf;
>     else
>         sgs[outcnt++] = &msg_buf;
> }

> > > +#ifdef CONFIG_PM_SLEEP
> > You could avoid this pair of ifdef by creating dummy versions of below
> > routines for !CONFIG_PM_SLEEP case. Up to you.
> 
> 
> Thank you. I'd like to keep the same.

Sure.

-- 
viresh