[U-Boot] [PATCH] pci: mx6: Implement reset callback

[Marek Vasut <marex@denx.de>]

On Monday, February 03, 2014 at 07:40:09 PM, Eric Nelson wrote:

[...]

> > Well ... SL and N6X both. For all I care, we can have #define
> > MX6_PCIE_RESET_GPIO and if that's not defined, puke out this warning. And
> > ultimatelly let this function be overriden anyway in case people used
> > some GPIO expander or whatnot. So the change to this would be:
> > 
> > __weak int imx6_pcie_toggle_reset(void)
> > {
> > #ifdef CONFIG_MX6_PCIE_RESET_GPIO
> > 
> >   gpio_set...
> >   mdelay();
> >   gpio_set...
> >   mdelay();
> > 
> > #else
> > 
> >   puts("Oh yeah, broken design :-(\n");
> 
> That's pretty harsh!

Yes, I know that won't please you :-(

> We have lots of stuff working without a GPIO...

Actually, see PCI Express Base Specification, Rev. 3.0 : Section 6.6.1 : 
Paragraph 2 . Quote:

"
6.6.1. Conventional Reset

Conventional Reset includes all reset mechanisms other than Function Level 
Reset. There are two categories of Conventional Resets: Fundamental Reset and 
resets that are not Fundamental Reset. This section applies to all types of 
Conventional Reset.

In all form factors and system hardware configurations, there must, at some 
level, be a hardware mechanism for setting or returning all Port states to the 
initial conditions specified in this document ? this mechanism is called 
?Fundamental Reset.? This mechanism can take the form of an auxiliary
signal provided by the system to a component or adapter card, in which case the 
signal must be called PERST#, and must conform to the rules specified in Section 
4.2.4.8.1. When PERST# is provided to a component or adapter, this signal must 
be used by the component or adapter as Fundamental Reset.

When PERST# is not provided to a component or adapter, Fundamental Reset is 
generated autonomously by the component or adapter, and the details of how this 
is done are outside the scope of this document. If a Fundamental Reset is 
generated autonomously by the component or adapter, and if power is supplied by 
the platform to the component/adapter, the component/adapter must generate a 
Fundamental Reset to itself if the supplied power goes outside of the limits 
specified for the form factor or system.
"

This means, your platform _MUST_ have a FR implementation. If you have PERST 
connected (that's the reset pin) to for example GPIO, then so be it and that's 
your FR.

The third paragraph states that if you do NOT have PERST connected, you need 
some other way of doing FR. Another way of generating FR is to depend on POR, so 
when power is applied to the component, it will generate FR internally. Thus to 
produce an "alternative" FR without PERST connected, you toggle the power GPIO 
of the particular slot.

I think the SL can do neither, right ? :-(

Best regards,
Marek Vasut