On 25 November 2012 17:22, Paul Carpenter
<[email protected]> wrote:
> Viresh Kumar wrote:
>> Add i2c bus recovery infrastructure to i2c adapters as specified in the
>> i2c
>> protocol Rev. 03 section 3.1.16 titled "Bus clear".
>>
>> http://www.nxp.com/documents/user_manual/UM10204.pdf
>
> You should also take note of section 3.1.14 and its notes on Software
> Reset -
> "Precautions must be taken to ensure that a device is not
> pulling down the SDA or SCL line after applying the supply
> voltage, since these low levels would block the bus"
Hmm.. This patch has taken a very long time for being accepted, and the
reason for that was, it was generalizing much more than what is required.
And I am not sure, if checking SCL low would be considered like that only. :)
@Wolfram: I would need your point of view on that, before trying it out.
>> +static int i2c_get_gpios_for_recovery(struct i2c_adapter *adap)
>> +{
>> + struct i2c_bus_recovery_info *bri = adap->bus_recovery_info;
>> + struct device *dev = &adap->dev;
>> + int ret = 0;
>
> Where is the check that SCL is NOT low (bus fault or device doing clock
> stretching)
Pending for Wolfram's point of view :)
>> +static int i2c_generic_recovery(struct i2c_adapter *adap)
>> +{
>> + /*
>> + * By this time SCL is high, as we need to give 9 falling-rising
>> edges
>> + */
>
> In my view that needs to be done by an actual check of the real SCL not
> assumption.
Checking that would be tricky. For GPIO recovery, we have to make it GPIO
first in input mode and read its value. Right?
>> + delay = DIV_ROUND_UP(delay, bri->clock_rate_khz * 2);
>> +
>> + for (i = 0; i < RECOVERY_CLK_CNT * 2; i++, val = !val) {
>> + bri->set_scl(adap, val);
>> + ndelay(delay);
>> +
>> + /* break if sda got high, check only when scl line is high */
>> + if (!bri->skip_sda_polling && val)
>
> Dont use 'val' read the actual SCL line which ensures you you are not
> wasting your time because of hardware fault. Possibly saving your GPIO
> from being stuck permanently.
Again, wolfram can decide if it is really required :)
--
viresh
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