[RFC] PCI: pci-imx6: Add delay to workaround kernel hang

[Shawn Guo]

On Thu, Jul 17, 2014 at 10:23:10AM +0200, Marek Vasut wrote:
> On Thursday, July 17, 2014 at 08:51:48 AM, Uwe Kleine-König wrote:
> > Hello,
> > 
> > On Tue, Jun 24, 2014 at 04:18:27PM -0300, Fabio Estevam wrote:
> > > From: Fabio Estevam <fabio.estevam at freescale.com>
> > > 
> > > When the mx6 PCI conctroller is initialized in the bootloader we see a
> > > kernel hang inside imx6_add_pcie_port().
> > > 
> > > Adding a 30ms delay allows the kernel to boot.
> > 
> > Just my thought on how to debug that: I'd try to bisect the pci init
> > routine in the boot loader. I.e. first only do the first half of the
> > initialisation in U-Boot. Depending on Linux being able to boot or not
> > initialize more or less on the next run.
> > 
> > Maybe there is a single register write that makes Linux fail?!
> 
> I am still hell-bent on thinking that the missing PCIe block reset is what makes 
> the Linux fail. Missing block reset is always a problem.

Indeed.  We're missing a hardware reset for PCIe on i.MX6Q and i.MX6DL.
Such reset is available on i.MX6SX, so there is no this problem for
i.MX6SX PCIe.

> Or do we now have a 
> mean to reset the PCIe block and it's PHY from software?

Richard is trying to find a SW workaround for it, but we're not really
sure if it's possible.

Shawn