linux-kernel - Re: [PATCH v6 2/4] power: reset: add reboot mode driver

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Date:	Mon, 28 Mar 2016 15:34:32 +0900
From:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
To:	Andy Yan <andy.yan@...k-chips.com>
Cc:	robh+dt@...nel.org, sre@...nel.org, heiko@...ech.de,
	john.stultz@...aro.org, arnd@...db.de, galak@...eaurora.org,
	ijc+devicetree@...lion.org.uk, catalin.marinas@....com,
	olof@...om.net, alexandre.belloni@...e-electrons.com,
	dbaryshkov@...il.com, jun.nie@...aro.org, pawel.moll@....com,
	will.deacon@....com, linux-rockchip@...ts.infradead.org,
	matthias.bgg@...il.com, devicetree@...r.kernel.org,
	linux-pm@...r.kernel.org, f.fainelli@...il.com,
	linux@....linux.org.uk, mbrugger@...e.com,
	linux-arm-kernel@...ts.infradead.org, lorenzo.pieralisi@....com,
	moritz.fischer@...us.com, linux-kernel@...r.kernel.org,
	wxt@...k-chips.com, dwmw2@...radead.org, mark.rutland@....com
Subject: Re: [PATCH v6 2/4] power: reset: add reboot mode driver

On 24.03.2016 17:03, Andy Yan wrote:
> Hi Krzystof:

(...)

>>> +static int get_reboot_mode_magic(struct reboot_mode_driver *reboot,
>>> +                                const char *cmd)
>>> +{
>>> +       const char *normal = "normal";
>>> +       int magic = 0;
>>> +       struct mode_info *info;
>>> +
>>> +       if (!cmd)
>>> +               cmd = normal;
>>> +
>>> +       list_for_each_entry(info, &reboot->head, list) {
>>> +               if (!strcmp(info->mode, cmd)) {
>>> +                       magic = info->magic;
>>> +                       break;
>>> +               }
>>> +       }
>>> +
>>> +       return magic;
>> In absence of 'normal' mode (it is not described as required property)
>> the magic will be '0'. It would be nice to document that in bindings.
>> Imagine someone forgets about this and will wonder why 0x0 is written
>> to his precious register on normal reboot...
> 
>     If the magic value is '0', we won't touch the register, please see
> reboot_mode_notify bellow.

Ah, indeed... so we cannot use value of '0' for magic (e.g. to clear any
existing value for normal reboot)?

>> It would be nice to document that 'mode-normal' has a special
>> (hard-coded) meaning.
>>
>>> +}
>>> +
>>> +static int reboot_mode_notify(struct notifier_block *this,
>>> +                             unsigned long mode, void *cmd)
>>> +{
>>> +       struct reboot_mode_driver *reboot;
>>> +       int magic;
>>> +
>>> +       reboot = container_of(this, struct reboot_mode_driver,
>>> reboot_notifier);
>>> +       magic = get_reboot_mode_magic(reboot, cmd);
>>> +       if (magic)
>>> +               reboot->write(magic);
>>> +
>>> +       return NOTIFY_DONE;
>>> +}
>>> +
>>> +int reboot_mode_register(struct device *dev, int (*write)(int))
>>> +{
>>> +       struct reboot_mode_driver *reboot;
>>> +       struct mode_info *info;
>>> +       struct property *prop;
>>> +       size_t len = strlen(PREFIX);
>>> +       int ret;
>>> +
>>> +       reboot = devm_kzalloc(dev, sizeof(*reboot), GFP_KERNEL);
>>> +       if (!reboot)
>>> +               return -ENOMEM;
>>> +
>>> +       reboot->write = write;
>>> +       INIT_LIST_HEAD(&reboot->head);
>>> +       for_each_property_of_node(dev->of_node, prop) {
>>> +               if (len > strlen(prop->name) || strncmp(prop->name,
>>> PREFIX, len))
>>> +                       continue;
>> New line please for readability.
> 
>     Okay
>>
>>> +               info = devm_kzalloc(dev, sizeof(*info), GFP_KERNEL);
>>> +               if (!info)
>>> +                       return -ENOMEM;
>> Ditto.
> 
>     Okay
>>
>>> +               strcpy(info->mode, prop->name + len);
>> Ehm, and how do you protect that name of mode is shorter than 32
>> characters?
> 
>     How about info->mode = prop->name + len ?

I don't get your answer.
As fair as I read the code, the prop->name can be very long and you are
copying it from 5 character. If the name of the mode has bazillion
characters then again my question: how do you protect that it will fit
in 32 bytes of 'mode'?


>>
>>> +               if (of_property_read_u32(dev->of_node, prop->name,
>>> &info->magic)) {
>>> +                       dev_err(dev, "reboot mode %s without magic
>>> number\n",
>>> +                               info->mode);
>>> +                       devm_kfree(dev, info);
>>> +                       continue;
>>> +               }
>>> +               list_add_tail(&info->list, &reboot->head);
>>> +       }
>>> +       reboot->reboot_notifier.notifier_call = reboot_mode_notify;
>>> +       ret = register_reboot_notifier(&reboot->reboot_notifier);
>>> +       if (ret)
>>> +               dev_err(dev, "can't register reboot notifier\n");
>>> +
>>> +       return ret;
>>> +}
>>> +EXPORT_SYMBOL_GPL(reboot_mode_register);
>>> +
>>> +MODULE_AUTHOR("Andy Yan <andy.yan@...k-chips.com");
>>> +MODULE_DESCRIPTION("System reboot mode driver");
>>> +MODULE_LICENSE("GPL v2");
>>> diff --git a/drivers/power/reset/reboot-mode.h
>>> b/drivers/power/reset/reboot-mode.h
>>> new file mode 100644
>>> index 0000000..44ed34f
>>> --- /dev/null
>>> +++ b/drivers/power/reset/reboot-mode.h
>>> @@ -0,0 +1,6 @@
>>> +#ifndef __REBOOT_MODE_H__
>>> +#define __REBOOT_MODE_H__
>>> +
>>> +int reboot_mode_register(struct device *dev, int (*write)(int));
>> Documentation would be appreciated. Although it is local header but
>> you decoupled them and you are exporting the function.
> 
>     I think I should remove the EXPORT_SYMBOL_GPL.

You need to export symbols which are located in modules. Is it located
in module?

Best regards,
Krzysztof