[PATCH] PCI: mediatek-gen3: Avoid PCIe resetting for Airoha EN7581 SoC

[Bjorn Helgaas]

On Mon, Sep 23, 2024 at 11:41:41AM +0200, AngeloGioacchino Del Regno wrote:
> Il 20/09/24 10:26, Lorenzo Bianconi ha scritto:
> > The PCIe controller available on the EN7581 SoC does not support reset
> > via the following lines:
> > - PCIE_MAC_RSTB
> > - PCIE_PHY_RSTB
> > - PCIE_BRG_RSTB
> > - PCIE_PE_RSTB
> > 
> > Introduce the reset callback in order to avoid resetting the PCIe port
> > for Airoha EN7581 SoC.
> 
> EN7581 doesn't support pulling up/down PERST#?!  That looks
> definitely odd, as that signal is part of the PCI-Express CEM spec.
> 
> Besides, there's another PERST# assertion at
> mtk_pcie_suspend_noirq()...

I agree, it doesn't smell right that this SoC doesn't have a way to
assert PERST#.

The response at
https://lore.kernel.org/r/SG2PR03MB63415DB5791C58C7EA69FF01FF682@SG2PR03MB6341.apcprd03.prod.outlook.com
suggests that maybe there's a hardware defect that means asserting
PERST# doesn't work correctly?  But surely firmware must have a way of
asserting PERST#, at least at boot time.

If this is truly a hardware defect and we really can't assert PERST#,
please say that this is a defect in the commit log so people don't
think that lack of PERST# is an acceptable thing.

Bjorn