linux-kernel - Re: [PATCH] MIPS: Loongson64: Add read_persistent

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Date:   Fri, 13 Nov 2020 11:41:01 +0800
From:   Tiezhu Yang <yangtiezhu@...ngson.cn>
To:     Jiaxun Yang <jiaxun.yang@...goat.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Huacai Chen <chenhc@...ote.com>
Cc:     linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        Xuefeng Li <lixuefeng@...ngson.cn>,
        Yinglu Yang <yangyinglu@...ngson.cn>,
        WANG Xuerui <git@...0n.name>
Subject: Re: [PATCH] MIPS: Loongson64: Add read_persistent_clock64()

On 11/13/2020 10:21 AM, Jiaxun Yang wrote:
>
>
> 在 2020/11/12 20:03, Tiezhu Yang 写道:
>> On 11/12/2020 06:09 PM, Jiaxun Yang wrote:
>>>
>>>
>>> 在 2020/11/12 18:04, Jiaxun Yang 写道:
>>>> Hi Tiezhu,
>>>>
>>>> 在 2020/11/12 16:29, Tiezhu Yang 写道:
>>>>> Add read_persistent_clock64() to read the time from the battery 
>>>>> backed
>>>>> persistent clock. With this patch, we can fix the wrong time issue 
>>>>> due
>>>>> to the system clock is not consistent with hardware clock after 
>>>>> resume
>>>>> from sleep state S3 (suspend to RAM), at the same time, the system 
>>>>> time
>>>>> can be right instead of "Thu Jan 1 08:00:00 CST 1970" without rtc 
>>>>> driver.
>>>>>
>>>>> start_kernel()
>>>>>    timekeeping_init()
>>>>>      read_persistent_wall_and_boot_offset()
>>>>>        read_persistent_clock64()
>>>>>
>>>>> timekeeping_resume()
>>>>>    read_persistent_clock64()
>>>>>
>>>>> timekeeping_suspend()
>>>>>    read_persistent_clock64()
>>>>
>>>> It is highly discoraged to do anything with bridgetype, which isn't 
>>>> probed via
>>>> devicetree.
>>>>
>>>> Please check if you can deal with that inside RTC framework, or 
>>>> make it as
>>>> a part of RTC driver (e.g. set up a callback).
>>>>
>>>> Also you should submit RTC driver at first if you intend to 
>>>> complete LS7A support.
>>>
>>> Oops,
>>> Just dig it deeper, I guess simply select RTC_HCTOSYS would solve 
>>> the issue.
>>> We're trying very hard to decouple all the drivers and conponents,
>>> DeviceTree for all!
>>
>> +cc WANG Xuerui <git@...0n.name>
>>
>> Hi Jiaxun,
>>
>> Thanks for your reply.
>>
>> Xuerui has already submitted the patch of LS7A rtc driver [1],
>> but not yet been merged into the mainline kernel, I discussed
>> with him early today.
>>
>> Do you mean that read_persistent_clock64() can call the function
>> like rtc_read_time() defined in rtc driver?
>
> I do think select RTC_HCTOSYS after getting RTC driver applied can help.

Yes, I agree.

> What's your point to have read_persistent_clock64 for Loongson64?

(1) Currently, the LS7A RTC driver has not been merged into the
mainline kernel, read_persistent_clock64() is useful in the following
call path:

start_kernel()
    timekeeping_init()
      read_persistent_wall_and_boot_offset()
        read_persistent_clock64()

(2) When the LS7A RTC driver is merged into the mainline kernel
some time later, if RTC_HCTOSYS and RTC_DRV_LS2X are not set,
read_persistent_clock64() is also useful unless RTC_HCTOSYS
and RTC_DRV_LS2X are set by default in Kconfig instead of
loongson3_defconfig.

So I think read_persistent_clock64() looks like a backup function.

>
> Thanks
>
> - Jiaxun
>
>>
>> Thanks,
>> Tiezhu
>>
>> [1] 
>> https://patchwork.kernel.org/project/linux-mips/patch/20200923075845.360974-2-git@xen0n.name/
>>
>>>
>>>>
>>>> Thanks.
>>>>
>>>> - Jiaxun
>>>>
>>>>>
>>>>> Signed-off-by: Yinglu Yang <yangyinglu@...ngson.cn>
>>>>> Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
>>>>> ---
>>>>>