linux-kernel - Re: [PATCH v5 3/5] misc: fuse: Add efuse driver for Tegra

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Date:	Fri, 30 May 2014 10:12:43 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Peter De Schrijver <pdeschrijver@...dia.com>
CC:	Russell King <linux@....linux.org.uk>,
	Thierry Reding <thierry.reding@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Wolfram Sang <wsa@...-dreams.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 3/5] misc: fuse: Add efuse driver for Tegra

On 05/30/2014 05:36 AM, Peter De Schrijver wrote:
> On Thu, May 29, 2014 at 09:04:33PM +0200, Stephen Warren wrote:
>> On 05/28/2014 06:54 AM, Peter De Schrijver wrote:
>>> Implement fuse driver for Tegra20, Tegra30, Tegra114 and Tegra124.
>>
>>> diff --git a/Documentation/ABI/testing/sysfs-driver-tegra-fuse b/Documentation/ABI/testing/sysfs-driver-tegra-fuse
>>
>>> +Description:	read-only access to the efuses on Tegra20, Tegra30, Tegra114
>>> +		and Tegra124 SoC's from NVIDIA. The efuses contain write once
>>> +		data programmed at the factory. The data is layed out in 32bit
>>> +		words in LSB first formnat. The number of valid bits depends
>>
>> s/formnat/format/
>>
>>> +		on the word and the SoC. The mapping is as follows:
>>> +
>>> +		For Tegra20:
>>> +		Word 0 - 1    : bit 0
>>> +		Word 2        : unused
>>> +		Word 3        : bits 0 - 31
>>> +		Word 4        : bits 0 - 7
>>
>> Do we really need these long tables that indicate which bits are used?
>> As I mentioned before, when I asked for documentation of the format of
>> these files, all I wanted was a brief not indicating that the data was
>> binary, and that each bit potentially represents a fuse... Either we
>> should leave it at that, or actually document what each bit represents,
>> which would hopefully be a pointless duplication of the TRM.
> 
> Some fuses are OEM defined, so there is no way to document all fuses there.
> Would you be ok with just dropping the tables then?

Yes.

> So, the description would become:
> 
> Description:    read-only access to the efuses on Tegra20, Tegra30, Tegra114
>                 and Tegra124 SoC's from NVIDIA. The efuses contain write once
>                 data programmed at the factory. The data is layed out in 32bit
>                 words in LSB first format. The number of valid bits depends
>                 on the word and the SoC.

Almost. That's still missing the key information that the data format is
one bit per fuse, and the ordering. Perhaps change from:

The data is layed out in 32bit words in LSB first format.

to:

The data is laid out in 32bit words in LSB first format. Each bit
represents a single fuse value. Bits order/assignment exactly matches
the HW registers, including any unused bits.
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