linux-kernel - Re: [PATCH v2 2/6] misc: fuse: Add efuse driver for Tegra

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Message-ID: <52CC666F.1010501@wwwdotorg.org>
Date:	Tue, 07 Jan 2014 13:41:19 -0700
From:	Stephen Warren <swarren@...dotorg.org>
To:	Peter De Schrijver <pdeschrijver@...dia.com>
CC:	"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>,
	Rob Landley <rob@...dley.net>,
	Thierry Reding <thierry.reding@...il.com>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	Danny Huang <dahuang@...dia.com>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v2 2/6] misc: fuse: Add efuse driver for Tegra

On 01/07/2014 07:05 AM, Peter De Schrijver wrote:
> On Mon, Jan 06, 2014 at 09:32:24PM +0100, Stephen Warren wrote:
>> On 12/24/2013 06:32 AM, Peter De Schrijver wrote:
>>> Implement fuse driver for Tegra20, Tegra30, Tegra114 and Tegra124.

>>> diff --git a/drivers/misc/fuse/tegra/fuse-tegra20.c b/drivers/misc/fuse/tegra/fuse-tegra20.c
>>
>>> +static int fuse_size;
>>
>> I don't think that's used.
>>
>>> +static u32 tegra20_fuse_readl(const unsigned int offset)
>> ...
>>> +	ret = tegra_apb_readl_using_dma(fuse_phys + FUSE_BEGIN + offset, &val);
>>
>> Shouldn't this use the generic tegra_apb_readl(), so that it works
>> irrespective of whether the Tegra20 APB DMA driver is available?
>
> tegra_apb_readl() doesn't work reliably on Tegra20 for reading the fuses.
> So if the Tegra20 APB DMA, this driver should also be unavailable.

There's no "depends TEGRA20_APB_DMA" in the Kconfig. Perhaps
ARCH_TEGRA_2x_SOC or FUSE_TEGRA should "select TEGRA20_APB_DMA"?

>>> +static int tegra_fuse_probe(struct platform_device *pdev)
>> ...
>>> +	fuse_randomness();
>>
>> If this is a driver, and particularly if this could be in a module, is
>> there any guarantee at all that fuse_randomness() gets called early
>> enough to be useful?
> 
> For a module this might be true yes... Should we disallow this making a
> module?

That would simplify things, I expect...

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