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

[Greg KH]

On Tue, Jul 16, 2013 at 11:02:22PM +0200, Oliver Schinagl wrote:
> 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 
> platform_get_data

That's not good, that shouldn't happen.

> >> 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 :)

Your code looks good, and correct, to me, I don't see anything obviously
wrong.  What creates your platform device in the first place?

> 
> 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, 
> sid_reg_base);
> 
> 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[] = {
>      &sid_bin_attr,
>      NULL,
> };
> 
> static const struct attribute_group sunxi_sid_group = {
>      .bin_attrs = sunxi_sid_attrs,
> };

If you create a "normal" attribute here as well, does that work
properly?

> 
> static const struct attribute_group *sunxi_sid_groups[] = {
>      &sunxi_sid_group,
>      NULL,
> };
> 
> 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

The memory locations are really different here, that's strange, I don't
know what is going on, sorry.

Try a text attribute to ensure that works properly.

greg k-h