From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
Clint Sbisa <csbisa@amazon.com>
Cc: linux-pci@vger.kernel.org, Bjorn Helgaas <helgaas@kernel.org>,
linux-arm-kernel@lists.infradead.org, will@kernel.org,
catalin.marinas@arm.com
Subject: Re: [PATCH] arm64: Enable PCI write-combine resources under sysfs
Date: Thu, 03 Sep 2020 09:07:00 +1000 [thread overview]
Message-ID: <edae1eeb0da578d941cfa5ad550eb0a0eda5f98e.camel@kernel.crashing.org> (raw)
In-Reply-To: <20200902164702.GA30611@e121166-lin.cambridge.arm.com>
On Wed, 2020-09-02 at 17:47 +0100, Lorenzo Pieralisi wrote:
> Yes I do and I expressed them.
>
> The first concern is the WC ambiguity on non-x86 systems, it looks
> like write combinining means everything and nothing at the same time
> on != x86 arches.
>
> On x86 prefetchable BAR == WC mapping (still conditional on arch
> features ie PAT, not a blanket enable). On ARM64 WC mapping currently
> corresponds to normal NC memory and the PCIe specs allow read
> side-effects BAR to be marked as prefetchable, I need to force PCI
> sig
> to remove the section I mentioned from the specifications because
> there
> is NO way it can be detected if a prefetchable BAR maps to read
> side-effects memory.
Im not sure I understand your sentence. It's been a long accepted rule
in PCI land that "prefetchable" BARs means "no side effects" and in
fact allows much more than just prefetching :-)
> A kernel device driver would (hopefully) know, sysfs code that just
> checks the prefetchable attribute and exports resource_WC does not.
>
> As I mentioned, if the mapping is done in a device specific driver it
> can be vetted and there are not many drivers mapping BARs as
> ioremap_wc().
It's been what other architectures have been doing for mroe than a
decade without significant issues... I don't think you should worry too
much about this.
Cheers,
Ben.
WARNING: multiple messages have this Message-ID (diff)
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
Clint Sbisa <csbisa@amazon.com>
Cc: linux-pci@vger.kernel.org, will@kernel.org,
Bjorn Helgaas <helgaas@kernel.org>,
linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com
Subject: Re: [PATCH] arm64: Enable PCI write-combine resources under sysfs
Date: Thu, 03 Sep 2020 09:07:00 +1000 [thread overview]
Message-ID: <edae1eeb0da578d941cfa5ad550eb0a0eda5f98e.camel@kernel.crashing.org> (raw)
In-Reply-To: <20200902164702.GA30611@e121166-lin.cambridge.arm.com>
On Wed, 2020-09-02 at 17:47 +0100, Lorenzo Pieralisi wrote:
> Yes I do and I expressed them.
>
> The first concern is the WC ambiguity on non-x86 systems, it looks
> like write combinining means everything and nothing at the same time
> on != x86 arches.
>
> On x86 prefetchable BAR == WC mapping (still conditional on arch
> features ie PAT, not a blanket enable). On ARM64 WC mapping currently
> corresponds to normal NC memory and the PCIe specs allow read
> side-effects BAR to be marked as prefetchable, I need to force PCI
> sig
> to remove the section I mentioned from the specifications because
> there
> is NO way it can be detected if a prefetchable BAR maps to read
> side-effects memory.
Im not sure I understand your sentence. It's been a long accepted rule
in PCI land that "prefetchable" BARs means "no side effects" and in
fact allows much more than just prefetching :-)
> A kernel device driver would (hopefully) know, sysfs code that just
> checks the prefetchable attribute and exports resource_WC does not.
>
> As I mentioned, if the mapping is done in a device specific driver it
> can be vetted and there are not many drivers mapping BARs as
> ioremap_wc().
It's been what other architectures have been doing for mroe than a
decade without significant issues... I don't think you should worry too
much about this.
Cheers,
Ben.
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next prev parent reply other threads:[~2020-09-02 23:09 UTC|newest]
Thread overview: 117+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-31 15:18 [PATCH] arm64: Enable PCI write-combine resources under sysfs Clint Sbisa
2020-08-31 23:24 ` Benjamin Herrenschmidt
2020-09-01 18:37 ` Bjorn Helgaas
2020-09-01 23:22 ` Benjamin Herrenschmidt
2020-09-02 8:57 ` Will Deacon
2020-09-02 11:32 ` Lorenzo Pieralisi
2020-09-02 14:29 ` Clint Sbisa
2020-09-02 16:47 ` Lorenzo Pieralisi
2020-09-02 16:47 ` Lorenzo Pieralisi
2020-09-02 17:21 ` Catalin Marinas
2020-09-02 17:21 ` Catalin Marinas
2020-09-02 17:54 ` Lorenzo Pieralisi
2020-09-02 17:54 ` Lorenzo Pieralisi
2020-09-02 23:03 ` Benjamin Herrenschmidt
2020-09-02 23:03 ` Benjamin Herrenschmidt
2020-09-02 23:08 ` Benjamin Herrenschmidt
2020-09-02 23:08 ` Benjamin Herrenschmidt
2020-09-02 23:08 ` Benjamin Herrenschmidt
2020-09-02 23:08 ` Benjamin Herrenschmidt
2020-09-02 23:07 ` Benjamin Herrenschmidt [this message]
2020-09-02 23:07 ` Benjamin Herrenschmidt
2020-09-03 11:08 ` Lorenzo Pieralisi
2020-09-03 11:08 ` Lorenzo Pieralisi
2020-09-03 14:36 ` Clint Sbisa
2020-09-03 14:36 ` Clint Sbisa
2020-09-03 22:26 ` Benjamin Herrenschmidt
2020-09-03 22:26 ` Benjamin Herrenschmidt
2020-09-07 23:33 ` Benjamin Herrenschmidt
2020-09-07 23:33 ` Benjamin Herrenschmidt
2020-09-10 9:46 ` Lorenzo Pieralisi
2020-09-10 9:46 ` Lorenzo Pieralisi
2020-09-10 10:54 ` Leon Romanovsky
2020-09-10 10:54 ` Leon Romanovsky
2020-09-10 12:37 ` Jason Gunthorpe
2020-09-10 12:37 ` Jason Gunthorpe
2020-09-10 15:17 ` Lorenzo Pieralisi
2020-09-10 15:17 ` Lorenzo Pieralisi
2020-09-10 17:10 ` Jason Gunthorpe
2020-09-10 17:10 ` Jason Gunthorpe
2020-09-10 21:46 ` Benjamin Herrenschmidt
2020-09-10 21:46 ` Benjamin Herrenschmidt
2020-09-10 23:29 ` Jason Gunthorpe
2020-09-10 23:29 ` Jason Gunthorpe
2020-09-11 0:39 ` Benjamin Herrenschmidt
2020-09-11 0:39 ` Benjamin Herrenschmidt
2020-09-11 14:21 ` Jason Gunthorpe
2020-09-11 14:21 ` Jason Gunthorpe
2020-09-11 21:42 ` Clint Sbisa
2020-09-11 21:42 ` Clint Sbisa
2020-09-14 14:17 ` Jason Gunthorpe
2020-09-14 14:17 ` Jason Gunthorpe
2020-09-14 14:24 ` Clint Sbisa
2020-09-14 14:24 ` Clint Sbisa
2020-09-14 14:38 ` Jason Gunthorpe
2020-09-14 14:38 ` Jason Gunthorpe
2020-09-14 21:42 ` Benjamin Herrenschmidt
2020-09-14 21:42 ` Benjamin Herrenschmidt
2020-09-14 22:00 ` Benjamin Herrenschmidt
2020-09-14 22:00 ` Benjamin Herrenschmidt
2020-09-14 22:32 ` Clint Sbisa
2020-09-14 22:32 ` Clint Sbisa
2020-09-14 22:57 ` Jason Gunthorpe
2020-09-14 22:57 ` Jason Gunthorpe
2020-09-14 23:25 ` Benjamin Herrenschmidt
2020-09-14 23:25 ` Benjamin Herrenschmidt
2020-09-15 10:18 ` Lorenzo Pieralisi
2020-09-15 10:18 ` Lorenzo Pieralisi
2020-09-15 11:05 ` Jason Gunthorpe
2020-09-15 11:05 ` Jason Gunthorpe
2020-09-15 23:17 ` Benjamin Herrenschmidt
2020-09-15 23:17 ` Benjamin Herrenschmidt
2020-09-15 23:40 ` Jason Gunthorpe
2020-09-15 23:40 ` Jason Gunthorpe
2020-09-16 7:59 ` Benjamin Herrenschmidt
2020-09-16 7:59 ` Benjamin Herrenschmidt
2020-09-16 12:12 ` Jason Gunthorpe
2020-09-16 12:12 ` Jason Gunthorpe
2020-09-16 14:09 ` Lorenzo Pieralisi
2020-09-16 14:09 ` Lorenzo Pieralisi
2020-09-16 14:14 ` Jason Gunthorpe
2020-09-16 14:14 ` Jason Gunthorpe
2020-09-16 23:59 ` Benjamin Herrenschmidt
2020-09-16 23:59 ` Benjamin Herrenschmidt
2020-09-17 10:28 ` Lorenzo Pieralisi
2020-09-17 10:28 ` Lorenzo Pieralisi
2020-09-17 11:32 ` Jason Gunthorpe
2020-09-17 11:32 ` Jason Gunthorpe
2020-09-17 14:01 ` Lorenzo Pieralisi
2020-09-17 14:01 ` Lorenzo Pieralisi
2020-09-17 16:08 ` Will Deacon
2020-09-17 16:08 ` Will Deacon
2020-09-16 12:48 ` Leon Romanovsky
2020-09-16 12:48 ` Leon Romanovsky
2020-09-16 8:33 ` Will Deacon
2020-09-16 8:33 ` Will Deacon
2020-09-16 8:48 ` Catalin Marinas
2020-09-16 8:48 ` Catalin Marinas
2020-09-16 14:15 ` Lorenzo Pieralisi
2020-09-16 14:15 ` Lorenzo Pieralisi
2020-09-16 17:00 ` Catalin Marinas
2020-09-16 17:00 ` Catalin Marinas
2020-09-16 21:29 ` Benjamin Herrenschmidt
2020-09-16 21:29 ` Benjamin Herrenschmidt
2020-09-16 12:08 ` Jason Gunthorpe
2020-09-16 12:08 ` Jason Gunthorpe
2020-09-15 23:00 ` Benjamin Herrenschmidt
2020-09-15 23:00 ` Benjamin Herrenschmidt
2020-09-15 23:12 ` Clint Sbisa
2020-09-15 23:12 ` Clint Sbisa
2020-09-14 21:41 ` Benjamin Herrenschmidt
2020-09-14 21:41 ` Benjamin Herrenschmidt
-- strict thread matches above, loose matches on Subject: below --
2020-08-21 15:51 Clint Sbisa
2020-08-21 15:51 ` Clint Sbisa
2020-08-27 14:41 ` Clint Sbisa
2020-08-27 14:41 ` Clint Sbisa
2020-08-31 15:22 ` Clint Sbisa
2020-08-31 15:22 ` Clint Sbisa
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