linux-kernel - Re: [PATCH] drivers, char: add U-Boot bootcount driver

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Message-id: <4F268EA1.3090907@denx.de>
Date:	Mon, 30 Jan 2012 13:35:45 +0100
From:	Heiko Schocher <hs@...x.de>
To:	Rob Herring <robherring2@...il.com>
Cc:	Wolfram Sang <w.sang@...gutronix.de>, Wolfgang Denk <wd@...x.de>,
	devicetree-discuss@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	Vitaly Bordug <vbordug@...mvista.com>,
	linux-watchdog@...r.kernel.org
Subject: Re: [PATCH] drivers, char: add U-Boot bootcount driver

Hello Rob,

Sorry for the late reply ...

Rob Herring wrote:
> On 12/06/2011 04:06 PM, Wolfram Sang wrote:
>>>> bootcount itself is not a device. It is a feature of certain devices. And that
>>>> needs to be implemented; possibly generic enough that it can work for register
>>>> based, i2c based, and so forth, accesses.
>>> If "boot counter" is not a good name for such a device, then what name
>>> would you suggest?
>> None.
>>
>>> Or do you think a counter (which can be implemented in a number of
>>> different ways, depending on hardware specifics) is not a device?
>> Yes.
>>
>>> What would be such a device, then?
>> "maxim,ds1338"
>>
>> Please have a look at the devicetree.org-wiki-page I just mentioned:
>>
>> http://devicetree.org/Device_Tree_Usage
>>
> 
> Perhaps fs/pstore would be a good choice for the user space interface
> (defining a new file bootcount). This can support any arbitrary backing
> device although pretty much only ACPI is implemented.

I tried to use fs/pstore for the bootcount feature, and I can mount
and read the bootcount value from the file, I created. But I could not
write to that file ... I only see the callback from
include/linux/pstore.h

struct pstore_info {
[...]
        int             (*write)(enum pstore_type_id type,
                        enum kmsg_dump_reason reason, u64 *id,
                        unsigned int part, size_t size, struct pstore_info *psi);

called, if I reboot ... do I miss something? Or is it not possible
to write to the files created through fs/pstore?

bye,
Heiko
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