[coreboot] Dealing with PCI reset

[Timothy Pearson]

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On 12/11/2016 03:48 PM, Paul Menzel via coreboot wrote:
> Dear coreboot folks,
> 
> 
> Several devices using the Intel 945 chipset copied code for PCI reset,
> costing 200 ms of boot time.
> 
> ```
>         /* Force PCIRST# */
>         pci_write_config16(PCI_DEV(0, 0x1e, 0), BCTRL, SBR);
>         udelay(200 * 1000);
>         pci_write_config16(PCI_DEV(0, 0x1e, 0), BCTRL, 0);
> ```
> 
> The change-set Ia37d9f0ecf5655531616edb20b53757d5d47b42f [1] removes
> that code from the Lenovo X60.
> 
> That code was added for some crypto card on a Roda device.
> 
> My question is, if removing that code is fine, or if it should be left
> in and be made configurable (Kconfig/NVRAM)?
> 
> Are there often cases where there are extensions card with problems,
> that need such a PCI reset?

We have run into this issue on the KGPE-D16 and LSI SAS controllers.
However, in this case it's not so much the reset itself as it is the
time it takes for the card to start up and become ready for PCI scan.

We handled this with a devicetree.cb option to set a delay between reset
and PCI scan.  Perhaps something similar could be used in this instance?

- -- 
Timothy Pearson
Raptor Engineering
+1 (415) 727-8645 (direct line)
+1 (512) 690-0200 (switchboard)
https://www.raptorengineering.com
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