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

Oliver Schinagl oliver at schinagl.nl
Tue Jul 16 17:02:22 EDT 2013

On 07/16/13 08:41, Greg KH wrote:
> On Mon, Jul 15, 2013 at 11:16:19PM +0200, Oliver Schinagl wrote:
>> With your latest patches for binary attributes and your blog post, I
>> thought that you want to create your binary attributes before the probe
>> function, to avoid the userspace race. To do that, we have two options,
>> create them in init (ugly?) or fill the .group member if available so it
>> gets automatically created from the register function.
> Yes, the .group thing should be what is needed here.
That's what I thought (and used).
>> Well in my case, I'm using the module_platform_driver() macro which
>> expects the struct platform_driver. Platform_driver has a device_driver
>> member .driver where the .groups is located. Great, using that works and
>> we should have the sysfs entry race-free. However I don't know hot to
>> exchange data between that and the rest of my driver.
>> Before I used to_platform_device(kobj_to_dev(kobj)) as passed via the
>> .read function to obtain a platform_device where i could use
>> platform_get_drvdata on. All was good, but that doesn't fly now and my
>> knowledge is a bit short as to why.
> I don't understand, why not use the platform device that was passed to
> the binary attribute write function?
Because the pointers don't match and I get a null pointer from 
>> The second method is finding some other shared structure given that we
>> get a platform_device in the probe function, yet I couldn't find
>> anything and this platform_device isn't the same as the one from the .read.
> It should be, why isn't it?
I think that's a little above my grasp :p
>> Of course using a global var bypasses this issue, but I'm sure it won't
>> pass review ;)
> The platform device structure should have what you need, right?
Should, but doesn't :(
>> So using these new patches for binary attributes, how can I pass data
>> between my driver and the sysfs files using a platform_driver? Or are
>> other 'hacks' needed and using the .groups attribute from
>> platform_driver->device_driver->groups is really the wrong approach.
>> I did ask around and still haven't figured it out so far, so I do
>> apologize if you feel I'm wasting your precious time.
> How is the platform device not the same thing that was passed to your
> probe function?
I don't know :( But i'll add the relevant sections with printk results 
below, which I should have done before, then again those printk's were 
not supposed to be in that e-mail to begin with ;)

So if I'm not seeing something stupidly obvious, feel free to shout at me :)

static ssize_t sid_read(struct file *fd, struct kobject *kobj,
             struct bin_attribute *attr, char *buf,
             loff_t pos, size_t size)
     struct platform_device *pdev;
     void __iomem *sid_reg_base;
     int i;

     pdev = to_platform_device(kobj_to_dev(kobj));
     sid_reg_base = (void __iomem *)platform_get_drvdata(pdev);
     printk("0x%p, 0x%p, 0x%p, 0x%p\n", kobj, kobj_to_dev(kobj), pdev, 

0xef1e7c80, 0xef1e7c78, 0xef1e7c68, 0x  (null)

     if (pos < 0 || pos >= SID_SIZE)
         return 0;
     if (size > SID_SIZE - pos)
         size = SID_SIZE - pos;

     for (i = 0; i < size; i++)
         buf[i] = sunxi_sid_read_byte(sid_reg_base, pos + i);

     return i;

static struct bin_attribute sid_bin_attr = {
     .attr = { .name = "eeprom", .mode = S_IRUGO, },
     .size = SID_SIZE,
     .read = sid_read,

static struct bin_attribute *sunxi_sid_attrs[] = {

static const struct attribute_group sunxi_sid_group = {
     .bin_attrs = sunxi_sid_attrs,

static const struct attribute_group *sunxi_sid_groups[] = {

static int __init sunxi_sid_probe(struct platform_device *pdev)
     struct resource *res;
     void __iomem *sid_reg_base;
     u8 entropy[SID_SIZE];
     unsigned int i;

     res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
     sid_reg_base = devm_ioremap_resource(&pdev->dev, res);
     if (IS_ERR(sid_reg_base))
         return PTR_ERR(sid_reg_base);
     platform_set_drvdata(pdev, sid_reg_base);

     for (i = 0; i < SID_SIZE; i++)
         entropy[i] = sunxi_sid_read_byte(sid_reg_base, i);
     add_device_randomness(entropy, SID_SIZE);
     dev_dbg(&pdev->dev, "%s loaded\n", DRV_NAME);
     printk("0x%p, 0x%p\n", pdev, sid_reg_base);

0xef02b000, 0xf1c23800

     return 0;

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