linux-kernel - Re: [PATCH v7 3/5] misc: fuse: Add efuse driver for Tegra

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Date:	Thu, 05 Jun 2014 12:37:26 -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-tegra@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 3/5] misc: fuse: Add efuse driver for Tegra

On 06/05/2014 07:09 AM, Peter De Schrijver wrote:
> Implement fuse driver for Tegra20, Tegra30, Tegra114 and Tegra124.
> 
> Signed-off-by: Peter De Schrijver <pdeschrijver@...dia.com>
> ---
>  Documentation/ABI/testing/sysfs-driver-tegra-fuse |   11 +
>  drivers/misc/fuse/Makefile                        |    1 +
>  drivers/misc/fuse/tegra/Makefile                  |    7 +
>  drivers/misc/fuse/tegra/fuse-tegra.c              |  250 +++++++++++++++++

I wonder if we shouldn't put this into drivers/soc/tegra?

> diff --git a/drivers/misc/fuse/tegra/fuse-tegra.c b/drivers/misc/fuse/tegra/fuse-tegra.c

> +void __init tegra_init_fuse(void)
> +{
> +	struct device_node *np;
> +	u32 id;
> +	void __iomem *car_base;
> +
> +	np = of_find_matching_node(NULL, apbmisc_match);
> +	apbmisc_base = of_iomap(np, 0);
> +	if (!apbmisc_base) {
> +		pr_warn("ioremap tegra apbmisc failed. using %08x instead\n",
> +			APBMISC_BASE);
> +		apbmisc_base = ioremap(APBMISC_BASE, APBMISC_SIZE);
> +	}
> +
> +	id = tegra_read_chipid();
> +	tegra_chip_id = (id >> 8) & 0xff;

So there's a fallback using APBMIS_BASE above if the node is missing, so
those last 2 lines always happen. However, if any of the following fail:

> +	strapping_base = of_iomap(np, 0);
...
> +	np = of_find_matching_node(NULL, tegra_fuse_match);
...
> +	np = of_find_matching_node(NULL, car_match);

Then this doesn't get executed:

> +	tegra_get_revision(id);

Isn't that important?

I guess that can't run if the lookup for tegra_fuse_match isn't
successful, since that tegra_get_revision may call
tegra20_spare_fuse_early() which uses fuse_base which is set up in
response to succesfully calling on of those node lookups. Isn't a
fallback needed there too?

I'm also a bit concerned that the driver probes, rather than the early
function tegra_init_fuse(), are doing things like setting up the speedo
data initialization, randomness addition, etc. For one, those won't
happen any more unless the DT nodes are present, and secondly,
triggering all those from driver probe rather than a function that's
called from the machine descriptor makes guaranteeing the timing
problematic.

I'd prefer to see the driver probes *just* set up the sysfs, and have
the code initialization stay unchanged relative to the code currently in
arch/arm/mach-tegra/ if possible.
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