Re: [PATCH v3 3/6] misc: fuse: Add efuse driver for Tegra

From: Stephen Warren
Date: Wed Feb 05 2014 - 14:16:02 EST

On 01/28/2014 04:36 PM, Peter De Schrijver wrote:
> Implement fuse driver for Tegra20, Tegra30, Tegra114 and Tegra124.

I assume most of this code is simply cut/paste from the existing code in
arch/arm/mach-tegra/? If so, "git format-patch -C" would have been
useful to highlight what changed when duplicating the files.

> diff --git a/Documentation/ABI/testing/sysfs-driver-tegra-fuse b/Documentation/ABI/testing/sysfs-driver-tegra-fuse
> +What: /sys/devices/*/<our-device>/fuse
> +Date: December 2013
> +Contact: Peter De Schrijver <pdeschrijver@xxxxxxxxxx>
> +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.
> +Users: any user space application which wants to read the efuses on
> + Tegra SoC's

Surely this file should describe the format of the file, since that's
part of the ABI too, right?

> diff --git a/drivers/misc/fuse/tegra/fuse-tegra20.c b/drivers/misc/fuse/tegra/fuse-tegra20.c

> +static int tegra20_fuse_probe(struct platform_device *pdev)
> + sku_info.revision = tegra_revision;
> + tegra20_init_speedo_data(&sku_info, &pdev->dev);
> +}
> +
> +static struct platform_driver tegra20_fuse_driver = {
> + .probe = tegra20_fuse_probe,
> + .driver = {
> + .name = "tegra20_fuse",
> + .owner = THIS_MODULE,
> + .of_match_table = tegra20_fuse_of_match,
> + }
> +};
> +
> +static int __init tegra20_fuse_init(void)
> +{
> + return platform_driver_register(&tegra20_fuse_driver);
> +}
> +postcore_initcall(tegra20_fuse_init);

That call to tegra20_init_speedo_data() now happens much later in boot.
Are you sure there's nothing that relies on data it sets up between when
tegra_fuse_init() is called (which is where it happens before this
series), and the somewhat arbitrary later time when this driver probes?

> diff --git a/drivers/misc/fuse/tegra/fuse-tegra30.c b/drivers/misc/fuse/tegra/fuse-tegra30.c

> +postcore_initcall(tegra30_fuse_init);
> +

There's a blank line at the end of the file. I thought checkpatch warned
about this? But actually it doesn't seem to at least in -f mode.

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

> +struct tegra_sku_info {
> + int sku_id;
> + int cpu_process_id;
> + int cpu_speedo_id;
> + int cpu_speedo_value;
> + int cpu_iddq_value;
> + int core_process_id;
> + int soc_speedo_id;
> + int gpu_speedo_id;
> + int gpu_process_id;
> + int gpu_speedo_value;
> + enum tegra_revision revision;
> +};

The only use of this appears to be to pass to tegra_fuse_create_sysfs()
which prints out the fields. Will there be more users in the future?
Otherwise, I'd be tempted to just print it out outside/before-calling

That said, I wonder if these values could/should be exposed in the sysfs
file to make it easier to interpret the fuses?

> diff --git a/drivers/misc/fuse/tegra/tegra114_speedo.c b/drivers/misc/fuse/tegra/tegra114_speedo.c

It might be nice to make these filenames consistent with the others,
e.g. fuse-speedo-tegraNNN.c/speedo-tegraNNN.c, or wrap them into

> diff --git a/drivers/misc/fuse/tegra/tegra30_speedo.c b/drivers/misc/fuse/tegra/tegra30_speedo.c

> +#define FUSE_SPEEDO_CALIB_0 0x14
> +#define FUSE_TEST_PROG_VER 0X28

In arch/arm/mach-tegra/tegra30_speedo.c, those values are different:

#define FUSE_SPEEDO_CALIB_0 0x114
#define FUSE_TEST_PROG_VER 0X128

Was this change intentional? Perhaps it should be in a separate patch to
highlight the change, if it's an intentional bug-fix?
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