[U-Boot] [PATCH v2 2/2] xilinx_xiic: Fix transfer initialisation

Marek Vasut marex at denx.de
Wed Jun 26 13:36:25 UTC 2019

On 6/26/19 3:19 PM, Melin Tomas wrote:
> On 6/26/19 3:48 PM, Marek Vasut wrote:
>> On 6/26/19 2:45 PM, Melin Tomas wrote:
>>> On 6/26/19 3:26 PM, Marek Vasut wrote:
>>>> On 6/26/19 2:19 PM, Melin Tomas wrote:
>>>>> On 6/26/19 2:49 PM, Marek Vasut wrote:
>>>>>> On 6/26/19 1:25 PM, Melin Tomas wrote:
>>>>>>> On 6/26/19 1:47 PM, Marek Vasut wrote:
>>>>>>>> On 6/26/19 12:39 PM, Melin Tomas wrote:
>>>>>>>>> As such, it's probably a good idea to keep the same delay values here as
>>>>>>>>> in the original driver unless good reason to use something else.
>>>>>>>>> As what goes for the original reasoning for 3ms, the commit history does
>>>>>>>>> not mention that so I cannot comment.
>>>>>>>> So would you be so kind and research this ?
>>>>>>> Based on a short study of other i2c bus drivers it seems most have bus
>>>>>>> busy timeout checks.
>>>>>>> The timeout values seems to differ, ranging from milliseconds to seconds.
>>>>>> Yep
>>>>>>> So probably it's just a number, after all it's just a check to know if
>>>>>>> we are good to go.
>>>>>> And is the number large enough ?
>>>>> As mentioned, good approach is probably using value known to work
>>>>> instead of
>>>>> guessing a new number.
>>>> So why did kernel pick that specific number ? Surely there was some
>>>> reasoning, they didn't just pull it out of /dev/random .
>>> Yes, history does not tell.
>>> I do see that this driver uses timeout of 1000ms for bus busy when
>>> probing, perhaps you can enlighten how that number was concluded? If
>>> that could give some clues about this.
>> I don't know.
> But you are author of that line?

+	ret = wait_for_bit_8(priv->base + XIIC_SR_REG_OFFSET,
+			     XIIC_SR_BUS_BUSY_MASK, false, 3, true);

comes from 2/2 ?

>> You're the patch author, it's your responsibility to know why you're
>> adding/changing the code you're adding/changing.
> yes, and the reasoning is:
> * the value has been deemed good in original driver. If it would be bad, 
> probably it would have been changed during course of time
> * the value has been tested for this driver as well with success

So shouldn't there be some upper bound on the bus busy time , demanded
either by the i2c bus spec or the xiic core spec ?

Best regards,
Marek Vasut

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