linux-kernel - Re: [PATCH v5 0/5] efuse driver for Tegra

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Message-ID: <5388AF2D.4060909@wwwdotorg.org>
Date:	Fri, 30 May 2014 10:17:49 -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 0/5] efuse driver for Tegra

On 05/30/2014 02:23 AM, Peter De Schrijver wrote:
> On Thu, May 29, 2014 at 09:01:27PM +0200, Stephen Warren wrote:
>> On 05/28/2014 06:54 AM, Peter De Schrijver wrote:
>>> This driver allows userspace to read the raw efuse data. Its userspace
>>> interface is modelled after the sunxi_sid driver which provides similar
>>> functionality for some Allwinner SoCs. It has been tested on
>>> Tegra20 (ventana), Tegra30 (beaverboard), Tegra114 (dalmore) and
>>> Tegra124 (jetson TK1).
>>
>>> Changes since v4:
>>>
>>> * Provide fallback to hardcoded 0x70000800 in case the apbmisc DT node is
>>>   missing. This is exactly what the current code does and prevents a system
>>>   crash in that case due to an invalid memory access by tegra_read_chipid()
>>
>> Wouldn't it be better to simply return an error?
> 
> This would mean you can't boot a system with these patches applied unless you
> also update the device tree. The system would crash during boot because CCF
> relies on tegra_read_chipid() as an APB barrier. Also tegra_boot_secondary()
> relies on the chipid to select the correct method for booting secondary cores.

Is this series really backwards-compatible anyway? tegra_init_fuse()
contains a whole bunch of places where resources are pulled out of DT,
and only one of those has a fallback to use APBMISC_BASE if the DT entry
isn't present.
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