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

[Eric Nelson]

Hi Marek,

On 02/03/2014 12:33 PM, Marek Vasut wrote:
> 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 :-(
>

Ouch!

>> 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 ? :-(
>

Right again.

PCIe was very much an afterthought (and late addition) on SABRE Lite,
and unfortunately only slightly improved on Nitrogen6x.

We have had success in using/testing PCIe devices without either, but
that doesn't mean we match the spec, and I suppose we'll have to live
with the "broken design" message...

Regards,


Eric