Subject: Re: [PATCH v1 0/6] misc: add reboot mode driver
To: Arnd Bergmann <arnd@arndb.de>
References: <1450774949-23901-1-git-send-email-andy.yan@rock-chips.com>
 <20151222164742.GA8623@piout.net> <567A6A01.8080305@rock-chips.com>
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Cc: Alexandre Belloni <alexandre.belloni@free-electrons.com>,
        robh+dt@kernel.org, heiko@sntech.de, john.stultz@linaro.org,
        sjg@chromium.org, treding@nvidia.com, galak@codeaurora.org,
        ijc+devicetree@hellion.org.uk, wxt@rock-chips.com,
        catalin.marinas@arm.com, olof@lixom.net, geert+renesas@glider.be,
        linux-rockchip@lists.infradead.org, dbaryshkov@gmail.com,
        sre@kernel.org, jun.nie@linaro.org, pawel.moll@arm.com,
        will.deacon@arm.com, akpm@linux-foundation.org,
        devicetree@vger.kernel.org, linux@arm.linux.org.uk,
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        linux-kernel@vger.kernel.org, mark.rutland@arm.com
From: Andy Yan <andy.yan@rock-chips.com>
Message-ID: <56823C86.5010008@rock-chips.com>
Date: Tue, 29 Dec 2015 15:55:50 +0800
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Hi Arnd:

On 2015年12月28日 23:28, Arnd Bergmann wrote:
> On Wednesday 23 December 2015 17:31:45 Andy Yan wrote:
>>      I also have the idea to put is in drivers/power/reset,  But considering
>>      this driver have not bind anything about power, so I put it in
>> driver/misc
>>      at last. So I hope if some people can give more suggestions here.
> I vote for drivers/power/reset as well. On some platforms, the two things
> are related, on others they are not, but it's good to have it all in one
> place I think.
     Okay, I will move to drivers/power/reset next version.
>>>>    drivers/soc/rockchip/Kconfig                       |  9 ++
>>>>    drivers/soc/rockchip/Makefile                      |  1 +
>>>>    drivers/soc/rockchip/reboot.c                     | 68 +++++++++++++++
>>> And maybe that part could be made generic instead of rockchip specific.
>>> It simply uses a regmap to do the accesses, I guess a lot of other
>>> platforms will do that. We have syscon-reboot and syscon-poweroff for example.
>>>
>>> I think then we can extend the "framework" by having generic drivers to
>>> store the value in eeprom or nvram for example.
>>>
>>      I also hope the write interface can be generic. But I found some
>> platform
>>      use different hardware to store the value. For example, John's patch
>> use
>>      SRAM on qcom apq8064 to store value for nexus7. It seems there also have
>>      some platform use dram or nvram to store it. And these different
>> hardware use
>>      different write method. I don't have a generic way to handle this.
>>
>>      I have a idea to handle it like this:
>>
>> +static const struct of_device_id reboot_mode_dt_match[] = {
>> +        { .compatible = "linux,reboot-mode-sfr",    /*for magic value
>> stored in special function register, which  can be accessed by regmap*/
>> +                .data = (void *)&reboot-mode-sfr },
> I'd make this one syscon-reboot-mode, to go along with syscon-poweroff
> as implemented by drivers/power/reset/syscon-poweroff.c. The syscon concept
> is already generic enough that we don't need a linux prefix for that.
     Okay, syscon is better.
>> +        { .compatible = "linux,reboot-mode-sram",  /*for magic value
>> stored in
>> +                .data = (void *)&reboot-mode-sram },
> the sram mode should probably follow the generic SRAM binding and make
> the location that stores the reboot mode a separate partition, unless
> we want to store other data in the same partition, in which case we might
> want to use the same implementation as for the nvram.
>
>> +        { .compatible = "linux,reboot-mode-sdram",
>> +                .data = (void *)&reboot-mode-sdram }, /*for magic value
>> stored
> I think "sdram" is not an appropriate name here, as the main system memory
> might use some other technology, e.g. DRAM or DDR2-SDRAM.
>
>> +        { .compatible = "rockchip,reboot-mode-nvram",
>> +                .data = (void *)&reboot-mode-nvram },
>> +        {},
>> +};
> nvram is a complex topic by itself, because there are so many ways to do it.
> I think what you are referring to here is a battery-backed memory that uses
> one or more bytes at a fixed offset to store a particular piece of information,
> as the drivers/char/nvram.c driver does. Maybe we should put the reboot mode
> into that driver then?
>
> There are other nvram drivers at various places in the kernel, and each may
> be slightly different, or completely different, like the EFIVARs driver on
> UEFI firmware or the key/value store on Open Firmware, these probably need
> their own methods and not share the generic driver.
>
>>      the data point to different hardware access method.
>>
>>     Hope to see more suggestions from you.
> It's probably best to leave these four examples as separate drivers and we can
> add further ones when needed.
>
> 	Arnd
>
>
     Okay, thanks for your suggestion.  I will add the reboot-mode.c as 
the core library, syscon-reboot-mode.c as one example first. As for 
sram/dram/nvram case, I am not familiar with them, so hope there are 
some hero will extend them when needed.


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