linux-kernel - Re: [EXT] Re: [v2] rtc: pcf85363/pcf85263: fix error that failed to run hwclock -w

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Message-ID: <21f417e3-db50-5930-ddc9-eed54f5d5893@vaisala.com>
Date:   Mon, 26 Aug 2019 12:17:11 +0300
From:   Nandor Han <nandor.han@...sala.com>
To:     Biwen Li <biwen.li@....com>, Leo Li <leoyang.li@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Mark Brown <broonie@...nel.org>
Cc:     "a.zummo@...ertech.it" <a.zummo@...ertech.it>,
        "linux-rtc@...r.kernel.org" <linux-rtc@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [EXT] Re: [v2] rtc: pcf85363/pcf85263: fix error that failed to
 run hwclock -w

On 8/26/19 7:29 AM, Biwen Li wrote:
>>
>> On 8/16/19 10:40 PM, Li Yang wrote:
>>> On Fri, Aug 16, 2019 at 11:30 AM Alexandre Belloni
>>> <alexandre.belloni@...tlin.com> wrote:
>>>>
>>>> On 16/08/2019 10:50:49-0500, Li Yang wrote:
>>>>> On Fri, Aug 16, 2019 at 3:05 AM Alexandre Belloni
>>>>> <alexandre.belloni@...tlin.com> wrote:
>>>>>>
>>>>>> On 16/08/2019 10:46:36+0800, Biwen Li wrote:
>>>>>>> Issue:
>>>>>>>       - # hwclock -w
>>>>>>>         hwclock: RTC_SET_TIME: Invalid argument
>>>>>>>
>>>>>>> Why:
>>>>>>>       - Relative patch:
>> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flkml.org
>> %2Flkml%2F2019%2F4%2F3%2F55&amp;data=02%7C01%7Cbiwen.li%40nxp.
>> com%7Cff8cebc3f1034ae3fa9608d725ff9e5e%7C686ea1d3bc2b4c6fa92cd99
>> c5c301635%7C0%7C0%7C637019652111923736&amp;sdata=spY6e22YOkOF
>> 3%2BF7crSM0M6xPmOhgULDqMZLQw%2BAmdI%3D&amp;reserved=0 , this
>> patch
>>>>>>>         will always check for unwritable registers, it will compare reg
>>>>>>>         with max_register in regmap_writeable.
>>>>>>>
>>>>>>>       - In drivers/rtc/rtc-pcf85363.c, CTRL_STOP_EN is 0x2e, but
>> DT_100THS
>>>>>>>         is 0, max_regiter is 0x2f, then reg will be equal to 0x30,
>>>>>>>         '0x30 < 0x2f' is false,so regmap_writeable will return false.
>>>>>>>
>>>>>>>       - Root cause: the buf[] was written to a wrong place in the file
>>>>>>>         drivers/rtc/rtc-pcf85363.c
>>>>>>>
>>>>>>
>>>>>> This is not true, the RTC wraps the register accesses properly and
>>>>>> this
>>>>>
>>>>> This performance hack probably deserve some explanation in the code
>>>>> comment.  :)
>>>>>
>>>>>> is probably something that should be handled by regmap_writable.
>>>>>
>>>>> The address wrapping is specific to this RTC chip.  Is it also
>>>>> commonly used by other I2C devices?  I'm not sure if regmap_writable
>>>>> should handle the wrapping case if it is too special.
>>>>>
>>>>
>>>> Most of the i2c RTCs do address wrapping which is sometimes the only
>>>> way to properly set the time.
>>>
>>> Adding Mark and Nandor to the loop.
>>>
>>> Regards,
>>> Leo
>>>
>>
>> Hi,
>>     `regmap` provides couple of ways to validate the registers:
>> max_register, callback function and write table. All of these are optional, so it
>> gives you the freedom to customize it as needed.
>>
>> In this situation probably you could:
>>     1. Avoid using the wrapping feature of pcf85363 (you can just provide
>> separate calls for stop, reset and time confguration). In this way the
>> `max_register` validation method will work fine.
> Yes, I use this way. Path as follows:
> Stop and reset - > set time > stop
> 

Some of the concerns regarding this method was that it might not be 
precise enough. That because you need 2 I2C operations (one for stop and 
one for time configuration). Not sure about your case if this is a 
problem or not.

>>     2. Replace `max_register` method validation with `callback function`
>> validation method, were you could make your own validation.
> It is not work, show the code in as follows:
> 
> bool regmap_writeable(struct regmap *map, unsigned int reg)
> {
>          if (map->max_register && reg > map->max_register)
>                  return false;
> Callback function (writeable_reg) will not be called.
>          if (map->writeable_reg)
>                  return map->writeable_reg(map->dev, reg);

Hi Li,
    If you *replace* the `max_register` method with `callback function` 
it should work. The code above will use every method *if provided*. In 
other words if `map->max_register` is 0 will go to the next step and 
check `map->writeable_reg`. Right?



Regards,
     Nandor