From: Lukas Wunner <lukas@wunner.de>
To: Nathan Rossi <nathan@nathanrossi.com>
Cc: linux-pci@vger.kernel.org, Nathan Rossi <nathan.rossi@digi.com>,
Bjorn Helgaas <bhelgaas@google.com>
Subject: Re: [PATCH] PCI: Add ACS errata for Pericom PI7C9X2G404 switch
Date: Fri, 3 Sep 2021 08:18:14 +0200 [thread overview]
Message-ID: <20210903061814.GA15994@wunner.de> (raw)
In-Reply-To: <20210903034029.306816-1-nathan@nathanrossi.com>
On Fri, Sep 03, 2021 at 03:40:29AM +0000, Nathan Rossi wrote:
> The Pericom PI7C9X2G404 PCIe switch has an errata for ACS P2P Request
> Redirect behaviour when used in the cut-through forwarding mode. The
> recommended work around for this issue is to use the switch in store and
> forward mode.
>
> This change adds a fixup specific to this switch that when enabling the
> downstream port it checks if it has enabled ACS P2P Request Redirect,
> and if so changes the device (via the upstream port) to use the store
> and forward operating mode.
From a quick look at the datasheet, this switch seems to support
hot-plug on its Downstream Ports:
https://www.diodes.com/assets/Datasheets/PI7C9X2G404SL.pdf
I think your quirk isn't executed if a device is hotplugged to an
initially-empty Downstream Port.
Also, if a device which triggered the quirk is hot-removed and none
of its siblings uses ACS P2P Request Redirect, cut-through forwarding
isn't reinstated.
Perhaps we need additional pci_fixup ELF sections which are used on
hot-add and hot-remove?
Thanks,
Lukas
next prev parent reply other threads:[~2021-09-03 6:18 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-03 3:40 [PATCH] PCI: Add ACS errata for Pericom PI7C9X2G404 switch Nathan Rossi
2021-09-03 6:18 ` Lukas Wunner [this message]
2021-09-06 6:01 ` Nathan Rossi
2021-09-08 22:24 ` Bjorn Helgaas
2021-09-09 8:08 ` Nathan Rossi
2021-09-09 17:52 ` Bjorn Helgaas
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