linux-kernel - Re: [PATCH v5] i2c: virtio: add a virtio i2c frontend driver

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Message-ID: <20210303093836.ftgq62yw7i6cd3q6@vireshk-i7>
Date:   Wed, 3 Mar 2021 15:08:36 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Jie Deng <jie.deng@...el.com>
Cc:     Alex Bennée <alex.bennee@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux-i2c@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, mst@...hat.com, wsa@...nel.org,
        jasowang@...hat.com, wsa+renesas@...g-engineering.com,
        andriy.shevchenko@...ux.intel.com, conghui.chen@...el.com,
        arnd@...db.de, kblaiech@...lanox.com,
        jarkko.nikula@...ux.intel.com, Sergey.Semin@...kalelectronics.ru,
        rppt@...nel.org, loic.poulain@...aro.org, tali.perry1@...il.com,
        u.kleine-koenig@...gutronix.de, bjorn.andersson@...aro.org,
        yu1.wang@...el.com, shuo.a.liu@...el.com,
        Stefan Hajnoczi <stefanha@...hat.com>
Subject: Re: [PATCH v5] i2c: virtio: add a virtio i2c frontend driver

On 03-03-21, 16:46, Jie Deng wrote:
> This is not a problem. My original proposal was to mirror the struct
> i2c_msg.
> The code you looked at was based on that.
> However, the virtio TC prefer not to mirror it. They have some concerns.
> For example, there is a bit I2C_M_RD in i2c_msg.flag which has the same
> meaning with
> the R/W in virtio descriptor. This is a repetition which may cause problems.
> So the virtio_i2c_out_hdr.flags is used to instead of i2c_msg.flags for
> extension.

So by default we don't support any of the existing flags except
I2C_M_RD?

#define I2C_M_TEN		0x0010	/* this is a ten bit chip address */
#define I2C_M_RD		0x0001	/* read data, from slave to master */
#define I2C_M_STOP		0x8000	/* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_NOSTART		0x4000	/* if I2C_FUNC_NOSTART */
#define I2C_M_REV_DIR_ADDR	0x2000	/* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_IGNORE_NAK	0x1000	/* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_NO_RD_ACK		0x0800	/* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_RECV_LEN		0x0400	/* length will be first received byte */

How do we work with clients who want to use such flags now ?

-- 
viresh