[PATCH v5 4/5] PCI: brcmstb: Don't assume 2711 bootloader leaves PERST# asserted

[Jim Quinlan]

On Tue, May 9, 2023 at 3:51 AM Cyril Brulebois <kibi at debian.org> wrote:
>
> Hi,
>
> Jim Quinlan <jim2101024 at gmail.com> (2023-05-08):
> > The current PCIe driver assumes PERST# is asserted when probe() is invoked.
> > The reasons are as follows:
> >
> > (1) One Broadcom SOC (7278) causes a panic if the PERST# register is
> >     written during this time window.
> >
> > (2) If PERST# is deasserted at Linux probe() time, experience and QA
> >     suspend/resume tests have shown that some endpoint devices fail if the
> >     PERST# is pulsed (deasserted => asserted => deasserted) quickly in this
> >     fashion, even though the timing is in accordance with their datasheets.
> >
> > (3) Keeping things in reset tends to save power, if for some reason the
> >     PCIe driver is not yet present.
> >
> > Broadcom STB and CM SOCs bootloaders always have PERST# asserted at
> > probe().  This is not necessarily the case for the 2711/RPi bootloader,
> > so, for 2711/RPi SOCs, do what Raspian OS does and assert PERST#.
> >
> > [1] https://lore.kernel.org/linux-pci/20230411165919.23955-1-jim2101024@gmail.com/T/#m39ebab8bc2827b2304aeeff470a6c6a58f46f987
>
> It would probably make sense to remove that [1] link entirely, to match
> the reference removal between v4 and v5.
Yep
>
>
> Cheers,
> --
> Cyril Brulebois (kibi at debian.org)            <https://debamax.com/>
> D-I release manager -- Release team member -- Freelance Consultant
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