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From: "Krzysztof Hałasa" <>
To: "Krzysztof Wilczyński" <>
Cc: Bjorn Helgaas <>,, Artem Lapkin <>,
	Neil Armstrong <>,
	Huacai Chen <>, Rob Herring <>,
	Lorenzo Pieralisi <>,
	Richard Zhu <>,
	Lucas Stach <>,
Subject: Re: [PATCH] PCIe: limit Max Read Request Size on i.MX to 512 bytes
Date: Fri, 13 Aug 2021 14:09:51 +0200	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <20210813101305.GA598827@rocinante> ("Krzysztof =?utf-8?Q?Wil?= =?utf-8?Q?czy=C5=84ski=22's?= message of "Fri, 13 Aug 2021 12:13:05 +0200")

Krzysztof, :-)

> Would it be possible to implement this particular MRRS fix as a quirk
> only for the i.MX6 controller?  Unless this is something that we need in
> the core, a quirk would be preferred over something that changes the PCI
> core.

I have briefly considered it, but I think it would be *much* more
complicated and error-prone. It also appears that there are more
platforms which need it - the old CNS3xxx, which currently subverts the
PCIE_BUS_PEER2PEER, the loongson, keystone, maybe all DWC PCIe.
Multiplication of the "quirk" code doesn't really look good to me.

TBH I don't think of this as of a "quirk" - all systems have MRRS
limits, it just happens that these ones have their limit lower than 4096
bytes. This isn't a limitation of a particular PCIe device, this is a
common limit of the whole system.

Also I'm not exactly sure the loongson fixup is complete.
It's only done at pci-enable*() time (e.g. for devices which have bigger
MRRS after power-up), while e.g. the r8169 driver changes MRRS well
after pci-enable*().

This means it needs to stay in/below pcie_get_readrq(), and while it
could mean going to ops->write*, it would be a real mess parsing the
devices, PCIE capabilities etc.
Now it's basically a few lines in a seldom called routine in pci.c, and
the loongson case (and others) can be made simpler (and really fixed) as
Krzysztof "Chris" Hałasa

Sieć Badawcza Łukasiewicz
Przemysłowy Instytut Automatyki i Pomiarów PIAP
Al. Jerozolimskie 202, 02-486 Warszawa

  reply	other threads:[~2021-08-13 12:10 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-13  8:52 Krzysztof Hałasa
2021-08-13 10:13 ` Krzysztof Wilczyński
2021-08-13 12:09   ` Krzysztof Hałasa [this message]
2021-08-13 19:22     ` Bjorn Helgaas
2021-08-16  5:18       ` Krzysztof Hałasa
2021-08-16  7:49         ` Richard Zhu
2021-08-16 11:18           ` Krzysztof Hałasa
2021-08-13 13:45 ` Rob Herring
2021-08-13 18:18   ` Krzysztof Hałasa

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