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

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Jim Quinlan <jim2101024@xxxxxxxxx> (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]

It would probably make sense to remove that [1] link entirely, to match
the reference removal between v4 and v5.

Cyril Brulebois (kibi@xxxxxxxxxx)            <>
D-I release manager -- Release team member -- Freelance Consultant

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