Re: i2c: ChromeOS EC tunnel driver

Re: i2c: ChromeOS EC tunnel driver

[Dave Jones]

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@chromium.org>
 > AuthorDate: Wed Apr 30 10:44:09 2014 -0700
 > Committer:  Lee Jones <lee.jones@linaro.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.

	Dave

Re: i2c: ChromeOS EC tunnel driver

[Doug Anderson]

Dave,

On Tue, Jun 10, 2014 at 7:33 AM, Dave Jones <davej@redhat.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@chromium.org>
>  > AuthorDate: Wed Apr 30 10:44:09 2014 -0700
>  > Committer:  Lee Jones <lee.jones@linaro.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