On Saturday 23 October 2021 14:45:34 Mauro Carvalho Chehab wrote: > Em Sat, 23 Oct 2021 12:40:11 +0200 > Pali Rohár <pali@xxxxxxxxxx> escreveu: > > It is classic setup for boards with just one PCIe port. > > > > > with 3 elements connected to the bus: an Ethernet card, a M.2 slot and > > > a mini PCIe slot. It seems HiKey 970 is unique with regards to PERST# signal, > > > as there are 4 independent PERST# signals there: > > > > > > - one for PEX 8606 (the PCIe root port); > > > - one for Ethernet; > > > - one for M.2; > > > - one for mini-PCIe. > > > > This is not unique setup, its pretty normal. Every PCIe card has (own) > > PERST# pin and obviously you want to control each pin separately via SW. > > And because PCIe switch is also (upstream) PCIe device it has also > > PERST# pin. > > Based on the discussions we had to add per-port DT PERST# gpios, it > sounded to me that this is was not a typical setup ;-) > > It seems that the typical setup is to have a single PERST# connected > to all devices inside the bus. Hello! I'm sure it is not unique :) Just seems that these boards either do not use device tree (x86-based) or do not have specified reset-gpios in DTS at all. Sometimes there is no need to touch PERST# gpio as either firmware during boot handles it (x86 BIOS/UEFI case, or U-Boot for arm case) or because board/cpu reset toggle PERST# in a way that is compatible for cards init. Looks like you have non-x86 board, which does not have PCIe init code in firmware, needs special handling of PERST# and you are doing it with upstream kernel :-) So maybe all these conditions are unique... But HW design not. As this setup with reset-gpios per card in DTS nodes is something which I will need too, I sent email to Rob with proposal how to universally declare it in DTS, independently of PCIe controller (you are on CC): https://lore.kernel.org/linux-pci/20211023144252.z7ou2l2tvm6cvtf7@pali/ Due to how PCIe cards are broken, PERST# signal is sometimes the only one option how to reset card at runtime. So requirement for separate PERST# per card configurable at runtime by OS will be requirement for more and more boards.
