[U-Boot] [PATCH v3 04/23] i2c: Add TPS6586X driver

[Stephen Warren]

On 04/09/2012 03:25 PM, Simon Glass wrote:
> Hi Stephen,
> 
> On Mon, Apr 9, 2012 at 2:01 PM, Stephen Warren <swarren at wwwdotorg.org> wrote:
>> On 04/02/2012 05:18 PM, Simon Glass wrote:
>>> This power management chip supports battery charging and a large number
>>> of power supplies. This initial driver only provides the ability to adjust
>>> the two synchronous buck converters SM0 and SM1 in a stepwise manner.
>>>
>>> Signed-off-by: Simon Glass <sjg at chromium.org>
>>
>>> +#define MAX_I2C_RETRY        3
>>> +int tps6586x_read(int reg)
>> ...
>>> +     for (i = 0; i < MAX_I2C_RETRY; ++i) {
>>> +             if (!i2c_read(I2C_ADDRESS, reg, 1, &data, 1)) {
>>> +                     retval = (int)data;
>>> +                     goto exit;
>>> +             }
>>> +
>>> +             /* i2c access failed, retry */
>>> +             udelay(100);
>>> +     }
>>
>> Why do we need this retry logic; the kernel driver doesn't appear to
>> have this.
> 
> We apparently have found the device to be flaky on i2c sometimes,
> which is why this is here.

Is it the device itself, or bad board layout/...? Do we need something
similar in the kernel?

In general though, if we're having problems communicating with the PMIC,
we're pretty screwed; how do we know whether failed transactions simply
fail (e.g. no ACK), or send bogus data to the PMIC (e.g. set some random
register so that something gets programmed to be over-voltage)? A better
solution might be a full system reset when you fail to communicate with
the PMIC.