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Date:   Tue, 9 May 2023 09:51:13 +0200
From:   Cyril Brulebois <kibi@debian.org>
To:     Jim Quinlan <jim2101024@gmail.com>
Cc:     linux-pci@vger.kernel.org,
        Nicolas Saenz Julienne <nsaenz@kernel.org>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Phil Elwell <phil@raspberrypi.com>,
        bcm-kernel-feedback-list@broadcom.com, james.quinlan@broadcom.com,
        Florian Fainelli <f.fainelli@gmail.com>,
        Lorenzo Pieralisi <lpieralisi@kernel.org>,
        Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= <kw@linux.com>,
        Rob Herring <robh@kernel.org>,
        "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" 
        <linux-rpi-kernel@lists.infradead.org>,
        "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" 
        <linux-arm-kernel@lists.infradead.org>,
        open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v5 4/5] PCI: brcmstb: Don't assume 2711 bootloader leaves
 PERST# asserted
Message-ID: <20230509075113.5cosbeaoykdoiefa@mraw.org>
Organization: Debian
References: <20230508220126.16241-1-jim2101024@gmail.com>
 <20230508220126.16241-5-jim2101024@gmail.com>
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Hi,

Jim Quinlan <jim2101024@gmail.com> (2023-05-08):
> The current PCIe driver assumes PERST# is asserted when probe() is invoke=
d.
> The reasons are as follows:
>=20
> (1) One Broadcom SOC (7278) causes a panic if the PERST# register is
>     written during this time window.
>=20
> (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 =3D> asserted =3D> deasserted) quickly i=
n this
>     fashion, even though the timing is in accordance with their datasheet=
s.
>=20
> (3) Keeping things in reset tends to save power, if for some reason the
>     PCIe driver is not yet present.
>=20
> 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#.
>=20
> [1] https://lore.kernel.org/linux-pci/20230411165919.23955-1-jim2101024@g=
mail.com/T/#m39ebab8bc2827b2304aeeff470a6c6a58f46f987

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


Cheers,
--=20
Cyril Brulebois (kibi@debian.org)            <https://debamax.com/>
D-I release manager -- Release team member -- Freelance Consultant

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