linux-kernel - Re: [PATCH 1/2] Initial support for Allwinner's Security ID fuses

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Message-ID: <20130602150946.GF18614@n2100.arm.linux.org.uk>
Date:	Sun, 2 Jun 2013 16:09:46 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Oliver Schinagl <oliver+list@...inagl.nl>
Cc:	maxime.ripard@...e-electrons.com, arnd@...db.de,
	gregkh@...uxfoundation.org, Oliver Schinagl <oliver@...inagl.nl>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/2] Initial support for Allwinner's Security ID fuses

On Sun, Jun 02, 2013 at 04:58:49PM +0200, Oliver Schinagl wrote:
> +#include <asm/io.h>

We have an include file called linux/io.h.  Please use linux/*.h files which
include asm/*.h files in preference to directly using asm/*.h.

In fact, no driver should include an asm/*.h header.

> +#include <linux/compiler.h>
> +#include <linux/device.h>
> +#include <linux/err.h>
> +#include <linux/errno.h>
> +#include <linux/export.h>
> +#include <linux/fs.h>
> +#include <linux/init.h>
> +#include <linux/kernel.h>
> +#include <linux/kobject.h>
> +#include <linux/module.h>
> +#include <linux/of_address.h>
> +#include <linux/platform_device.h>
> +#include <linux/random.h>
> +#include <linux/stat.h>
> +#include <linux/sysfs.h>
> +#include <linux/types.h>
> +
> +#define DRV_NAME "sunxi-sid"
> +#define DRV_VERSION "1.0"
> +
> +/* There are 4 32-bit keys */
> +#define SID_KEYS 4
> +/* and 4 byte sized keys per 32-bit key */
> +#define SID_SIZE (SID_KEYS * 4)
> +
> +static void __iomem *p_sid_reg_base;
> +
> +/* We read the entire key, but only return the requested byte. This is of
> + * course slower then it could be and uses 4 times more reads as needed but
> + * keeps code a simpler.
> + */
> +u8 sunxi_sid_read_byte(const int offset)
> +{
> +	u32 sid_key;
> +	u8 ret;
> +
> +	ret = 0;
> +
> +	if (likely((SID_SIZE))) {
> +		sid_key = ioread32be(p_sid_reg_base + round_down(offset, 4));
> +		sid_key >>= (offset % 4) * 8;
> +		ret = sid_key & 0xff;
> +	}

What happens if you unbind the device in sysfs and then try and use
this function?

> +static int sunxi_sid_remove(struct platform_device *pdev)
> +{
> +	device_remove_bin_file(&pdev->dev, &sid_bin_attr);
> +	dev_info(&pdev->dev, "Sunxi SID driver unloaded successfully.\n");

Maybe you want to set p_sid_reg_base to NULL here?

> +
> +	return 0;
> +}
> +
> +static int __init sunxi_sid_probe(struct platform_device *pdev)
> +{
> +	int entropy[SID_SIZE], i, ret;
> +	struct device *dev;
> +	struct resource *res;
> +	void __iomem *sid_reg_base;
> +
> +	dev = &pdev->dev;
> +	if (unlikely(!pdev->dev.of_node)) {
> +		dev_err(dev, "No devicetree data available\n");
> +		ret = -EFAULT;
> +		goto exit;
> +	}
> +
> +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +	sid_reg_base = devm_ioremap_resource(&pdev->dev, res);
> +	if (IS_ERR(sid_reg_base)) {
> +		dev_err(dev, "Unable to obtain resource\n");
> +		ret = PTR_ERR(sid_reg_base);
> +		goto exit;
> +	}
> +	platform_set_drvdata(pdev, sid_reg_base);
> +	p_sid_reg_base = sid_reg_base;

So what happens if you have two of these devices?  Maybe you want to check
whether p_sid_reg_base is already set?

> +
> +	ret = device_create_bin_file(dev, &sid_bin_attr);
> +	if (unlikely(ret)) {
> +		dev_err(dev, "Unable to create sysfs bin entry\n");
> +		goto exit;
> +	}
> +
> +	for (i = 0; i < SID_SIZE; i++)
> +		entropy[i] = sunxi_sid_read_byte(i);
> +	add_device_randomness(entropy, SID_SIZE);
> +
> +	dev_info(dev, "Sunxi SID driver loaded successfully.\n");

Do we really need to report that the driver "loaded successfully" ?
Do we need lots of lines in the kernel log telling us simply that
random driver X was built into the kernel or the module was loaded?
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