linux-kernel - Re: i2c: ChromeOS EC tunnel driver

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Message-ID: <CAD=FV=Wx2kuEHSebDQcrZs19o+7OAVo_WNNROoTwEkFc6xpqzQ@mail.gmail.com>
Date:	Tue, 10 Jun 2014 08:39:40 -0700
From:	Doug Anderson <dianders@...omium.org>
To:	Dave Jones <davej@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Douglas Anderson <dianders@...omium.org>,
	Lee Jones <lee.jones@...aro.org>
Subject: Re: i2c: ChromeOS EC tunnel driver

Dave,

On Tue, Jun 10, 2014 at 7:33 AM, Dave Jones <davej@...hat.com> wrote:
> On Fri, Jun 06, 2014 at 07:31:28PM +0000, Linux Kernel wrote:
>  > Gitweb:     http://git.kernel.org/linus/;a=commit;h=9d230c9e4f4e67cb1c1cb9e0f6142da16b0f2796
>  > Commit:     9d230c9e4f4e67cb1c1cb9e0f6142da16b0f2796
>  > Parent:     5271db29d7199fe0ffb303ca4bbbb1485bba28c3
>  > Refname:    refs/heads/next
>  > Author:     Doug Anderson <dianders@...omium.org>
>  > AuthorDate: Wed Apr 30 10:44:09 2014 -0700
>  > Committer:  Lee Jones <lee.jones@...aro.org>
>  > CommitDate: Tue Jun 3 08:11:49 2014 +0100
>
>  > +static int ec_i2c_construct_message(u8 *buf, const struct i2c_msg i2c_msgs[],
>  > +                                int num, u16 bus_num)
>  > +{
>  > +    struct ec_params_i2c_passthru *params;
>  > +    u8 *out_data;
>  > +    int i;
>  > +
>  > +    out_data = buf + sizeof(struct ec_params_i2c_passthru) +
>  > +               num * sizeof(struct ec_params_i2c_passthru_msg);
>  > +
>  > +    params = (struct ec_params_i2c_passthru *)buf;
>  > +    params->port = bus_num;
>  > +    params->num_msgs = num;
>  > +    for (i = 0; i < num; i++) {
>  > +            const struct i2c_msg *i2c_msg = &i2c_msgs[i];
>  > +            struct ec_params_i2c_passthru_msg *msg = &params->msg[i];
>  > +
>  > +            msg->len = i2c_msg->len;
>  > +            msg->addr_flags = i2c_msg->addr;
>  > +
>  > +            if (i2c_msg->flags & I2C_M_TEN)
>  > +                    msg->addr_flags |= EC_I2C_FLAG_10BIT;
>
> This is a fun bug. EC_I2C_FLAG_10BIT is 1<<16, but msg->addr_flags is only a uint16.

Good catch.  Luckily we have no actual 10-bit devices on the other
end, but it sure makes this bit of the tunnel pretty stupid.

The correct fix is to fix the master 'ec_commands.h' in the ChromeOS
EC project, then pull the change over to the kernel.  I've filed a bug
against our EC team at http://crbug.com/382944

-Doug
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