Re: How does Linux handle PCI-E Surprise unplug?

[Greg KH <greg@kroah.com>]

On Fri, Feb 19, 2010 at 09:31:46AM +0530, Rajat Jain wrote:
> > The driver will suddenly start reading all 0xff and will then need to
> > abort whatever it was doing.  Usually all drivers handle this just
> fine
> > today, as this is what they needed to do when they were pccard
> devices.
> > Nothing new here at all.
> 
> It is fairly common for the drivers to have such code:
> 
> Val1 = ioread32(reg1);
> Val2 = ioread32(reg2);
> Val3 = ioread32(reg3);
> Val4 = ioread32(reg4);
> 
> Do you mean the above code is wrong and it should be re-written as:
> 
> If ((Val1 = ioread32(reg1)) = 0xFFFFFFFF)
> 	/* Abort */
> If ((Val2 = ioread32(reg2)) = 0xFFFFFFFF)
> 	/* Abort */
> Etc ....

No, they can check the last one, or something every once in a while.

> Checking for 0xFFFFFFFF at every read is a pain, don't you think so? And
> more over, what is a register ACTUALLY contains the value 0xFFFFFFFF?
> How do we differentiate this with the case when the device has been
> plugged out?

Test a value that you know will not be this one.

> Finally, how do we re-write the following code to handle this correctly?
> 
> iowrite32(val1, reg1);
> iowrite32(val2, reg2);
> iowrite32(val3, reg3);
> iowrite32(val4, reg4);

You wait until you do a read :)

Seriously, look at the existing drivers in the kernel, they should all
handle this just fine.

thanks,

greg k-h