From: Bjorn Helgaas <helgaas@kernel.org>
To: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: "Huacai Chen" <chenhuacai@loongson.cn>,
"Bjorn Helgaas" <bhelgaas@google.com>,
"Lorenzo Pieralisi" <lorenzo.pieralisi@arm.com>,
"Rob Herring" <robh@kernel.org>,
"Krzysztof Wilczyński" <kw@linux.com>,
linux-pci <linux-pci@vger.kernel.org>,
"Xuefeng Li" <lixuefeng@loongson.cn>,
"Huacai Chen" <chenhuacai@gmail.com>,
"Jingoo Han" <jingoohan1@gmail.com>,
"Gustavo Pimentel" <gustavo.pimentel@synopsys.com>,
"Kishon Vijay Abraham I" <kishon@ti.com>,
"Krzysztof Hałasa" <khalasa@piap.pl>
Subject: Re: [PATCH V13 4/6] PCI: loongson: Improve the MRRS quirk for LS7A
Date: Fri, 3 Jun 2022 19:07:12 -0500 [thread overview]
Message-ID: <20220604000712.GA118018@bhelgaas> (raw)
In-Reply-To: <f336dd51-a6f2-4168-9e4b-1a6dc3d7da6a@www.fastmail.com>
On Fri, Jun 03, 2022 at 11:57:47PM +0100, Jiaxun Yang wrote:
> 在2022年6月2日六月 下午5:20,Bjorn Helgaas写道:.
> >
> > I'd really like to have a single implementation of whatever quirk
> > works around this. I don't think we should have multiple copies
> > just because we assume some firmware takes care of part of this
> > for us.
> >
> Yeah that was my idea when I was writing the present version of
> workaround. However in later LS7A revisions Loongson somehow raised
> MRRS for several PCIe controllers on chip to 1024 and other ports
> remains to be 256. Kernel have no way to aware of this change and we
> can only rely on firmware to set proper value.
That's fine; we need a controller-specific way to find the limit
(whether it's fixed for all versions or discovered from firmware
settings or whatever).
My hope is that given that controller-specific value, we can have a
single quirk that works on keystone, loongson, etc. to enforce the
limit on all relevant devices. Some platform firmware might do that
configuration already, but it's OK if a generic quirk re-does it.
I don't think it's worth having two quirks, one that does the
configuration, and another that relies on firmware having done it.
> I have no idea how Loongson achieved this in hardware. All those
> PCIe controllers are attached under the same AXI bus should share
> the same AXI to HyperTransport bridge as AXI slave behind a bus
> matrix. Perhaps instead of fixing error handling of their AXI
> protocol implementation they just increased the buffer size in AXI
> bridge so it can accomplish larger requests at one time.
> >> In keystone’s case it’s likely that their firmware won’t do such thing, so
> >> their workaround shouldn’t be removed.
> >> And no_inc_mrrs should be set for them to prevent device drivers modifying
> >> MRRS afterwards.
> >
> > I have the vague impression that this issue is related to an arm64 AXI
> > bus property [2] or maybe a DesignWare controller property [3], so
> > this might affect several PCIe controller drivers.
>
> In my understanding it’s likely to be a AXI implementation issue.
I know almost nothing about AXI, but this concerns me because it
sounds like other drivers could be affected.
Bjorn
next prev parent reply other threads:[~2022-06-04 0:07 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-30 8:48 [PATCH V13 0/6] PCI: Loongson pci improvements and quirks Huacai Chen
2022-04-30 8:48 ` [PATCH V13 1/6] PCI: loongson: Use generic 8/16/32-bit config ops on LS2K/LS7A Huacai Chen
2022-06-01 2:08 ` Bjorn Helgaas
2022-06-02 4:18 ` Huacai Chen
2022-04-30 8:48 ` [PATCH V13 2/6] PCI: loongson: Add ACPI init support Huacai Chen
2022-05-31 23:04 ` Bjorn Helgaas
2022-06-02 7:09 ` Huacai Chen
2022-04-30 8:48 ` [PATCH V13 3/6] PCI: loongson: Don't access unexisting devices Huacai Chen
2022-05-31 23:14 ` Bjorn Helgaas
2022-06-02 4:28 ` Huacai Chen
2022-06-02 16:23 ` Bjorn Helgaas
2022-06-02 20:00 ` Jiaxun Yang
2022-04-30 8:48 ` [PATCH V13 4/6] PCI: loongson: Improve the MRRS quirk for LS7A Huacai Chen
2022-06-01 2:22 ` Bjorn Helgaas
2022-06-01 11:59 ` Jiaxun Yang
2022-06-02 4:17 ` Huacai Chen
2022-06-02 16:20 ` Bjorn Helgaas
2022-06-03 12:13 ` Krzysztof Hałasa
2022-06-03 22:57 ` Jiaxun Yang
2022-06-04 0:07 ` Bjorn Helgaas [this message]
2022-06-08 8:29 ` Huacai Chen
2022-04-30 8:48 ` [PATCH V13 5/6] PCI: Add quirk for LS7A to avoid reboot failure Huacai Chen
2022-05-31 23:35 ` Bjorn Helgaas
2022-06-02 12:48 ` Huacai Chen
2022-06-02 16:29 ` Bjorn Helgaas
2022-06-08 9:34 ` Huacai Chen
2022-06-08 19:31 ` Bjorn Helgaas
2022-06-16 8:39 ` Huacai Chen
2022-06-16 22:57 ` Bjorn Helgaas
2022-06-17 2:21 ` Huacai Chen
2022-06-17 11:37 ` Bjorn Helgaas
2022-06-17 12:14 ` Huacai Chen
2022-04-30 8:48 ` [PATCH V13 6/6] PCI: Add quirk for multifunction devices of LS7A Huacai Chen
2022-06-01 2:07 ` Bjorn Helgaas
2022-06-01 7:36 ` Jianmin Lv
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