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From: Guy Crazy <superymk.adv@gmail.com>
To: linux-kernel@vger.kernel.org
Subject: A Question about the patch "[PATCH v8 3/4] PCI: Introduce disable_acs_redir quirk"
Date: Mon, 7 Oct 2019 16:25:49 -0400	[thread overview]
Message-ID: <CAPPcaqPhQ2jJ=wRHf5_hVQAT-9gtn7EZv4y+68dEzgsZv7pTMw@mail.gmail.com> (raw)

Hi,

I have a question about this patch from the web link
(https://lwn.net/ml/linux-kernel/20180730161840.13733-4-logang@deltatee.com/).
According to the PCIe spec (PCIe 3.0), ACS Upstream Forwarding (UF)
seems quite similar with Request Redirect (RR). Why
pci_quirk_disable_intel_spt_pch_acs_redir in this patch seems disable
RR but not UF?

One related question in further: what's the difference between UF and
RR (examples preferred)? Both seems redirect traffics originated from
downstreams. Especially I feel confused about UF in the PCIe spec:
PCIe switches must always route upstream requests towards RC because
they target upstream destinations, why these switches need UF config?

Thanks!

                 reply	other threads:[~2019-10-07 20:26 UTC|newest]

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