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

From: Nandor Han <nandor.han@vaisala.com>
To: Li Yang <leoyang.li@nxp.com>,
	Alexandre Belloni <alexandre.belloni@bootlin.com>,
	Mark Brown <broonie@kernel.org>
Cc: Biwen Li <biwen.li@nxp.com>,
	a.zummo@towertech.it, linux-rtc@vger.kernel.org,
	lkml <linux-kernel@vger.kernel.org>
Subject: Re: [v2] rtc: pcf85363/pcf85263: fix error that failed to run hwclock -w
Date: Wed, 21 Aug 2019 09:20:05 +0300	[thread overview]
Message-ID: <ff198737-acb5-7186-7e14-a1e1cdc0f72c@vaisala.com> (raw)
In-Reply-To: <CADRPPNQwcGrVXLm8eHbXKmyecMhT6Mt9rNGnspJA1+MnV4K8oQ@mail.gmail.com>

On 8/16/19 10:40 PM, Li Yang wrote:
> On Fri, Aug 16, 2019 at 11:30 AM Alexandre Belloni
> <alexandre.belloni@bootlin.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@bootlin.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://lkml.org/lkml/2019/4/3/55 , 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.
   2. Replace `max_register` method validation with `callback function` 
validation method, were you could make your own validation.

Regards,
    Nandor