From: Catalin Marinas <catalin.marinas@arm.com>
To: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Leon Romanovsky <leon@kernel.org>,
linux-pci@vger.kernel.org, Bjorn Helgaas <helgaas@kernel.org>,
Jason Gunthorpe <jgg@nvidia.com>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Will Deacon <will@kernel.org>,
linux-arm-kernel@lists.infradead.org,
Clint Sbisa <csbisa@amazon.com>
Subject: Re: [PATCH] arm64: Enable PCI write-combine resources under sysfs
Date: Wed, 16 Sep 2020 18:00:59 +0100 [thread overview]
Message-ID: <20200916170058.GD3122@gaia> (raw)
In-Reply-To: <20200916141502.GB20770@e121166-lin.cambridge.arm.com>
On Wed, Sep 16, 2020 at 03:15:02PM +0100, Lorenzo Pieralisi wrote:
> On Wed, Sep 16, 2020 at 09:48:52AM +0100, Catalin Marinas wrote:
> > On Wed, Sep 16, 2020 at 09:33:16AM +0100, Will Deacon wrote:
> > > On Tue, Sep 15, 2020 at 08:40:06PM -0300, Jason Gunthorpe wrote:
> > > > On Wed, Sep 16, 2020 at 09:17:38AM +1000, Benjamin Herrenschmidt wrote:
> > > > > With the patch, those device will now use MT_DEVICE_NC.
> > > >
> > > > Which doesn't do WC at all on some ARM implementations.
> > >
> > > Is that just TX2? I remember that thing being weird where GRE performed
> > > better than NC, but I thought that was a one off (and the thing is dead).
> >
> > I recall something along these lines. Hopefully ARM updated the guidance
> > to licensees.
> >
> > > NC is more permissive than GRE, so I think that's the right one to use; i.e.
> > > we go for the fewest number of restrictions on the hardware. If somebody
> > > screws up the uarch, that's up to them.
> >
> > I agree, Normal NC is better as long as the BAR can tolerate read
> > side-effects.
>
> That we don't know but if a prefetchable BAR can't tolerate read
> side effects this would be already a problem on eg x86 - that's
> the best we can hope for given the current PCI specs.
>
> +1 on normal NC. The only open point is whether we should make
> arch_can_pci_mmap_wc() return false on platforms like TX2.
I lost track in this thread whether it matters. TX2 would need Device
GRE for optimal performance but the kernel doesn't currently provide it
anyway. We could expose a new memory type, aligned_wc ;).
--
Catalin
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next prev parent reply other threads:[~2020-09-16 17:02 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20200831151827.pumm2p54fyj7fz5s@amazon.com>
[not found] ` <20200902113207.GA27676@e121166-lin.cambridge.arm.com>
[not found] ` <20200902142922.xc4x6m33unkzewuh@amazon.com>
2020-09-02 16:47 ` [PATCH] arm64: Enable PCI write-combine resources under sysfs Lorenzo Pieralisi
2020-09-02 17:21 ` Catalin Marinas
2020-09-02 17:54 ` Lorenzo Pieralisi
2020-09-02 23:03 ` Benjamin Herrenschmidt
2020-09-02 23:08 ` Benjamin Herrenschmidt
2020-09-02 23:08 ` Benjamin Herrenschmidt
2020-09-02 23:07 ` Benjamin Herrenschmidt
2020-09-03 11:08 ` Lorenzo Pieralisi
2020-09-03 14:36 ` Clint Sbisa
2020-09-03 22:26 ` Benjamin Herrenschmidt
2020-09-07 23:33 ` Benjamin Herrenschmidt
2020-09-10 9:46 ` Lorenzo Pieralisi
2020-09-10 10:54 ` Leon Romanovsky
2020-09-10 12:37 ` Jason Gunthorpe
2020-09-10 15:17 ` Lorenzo Pieralisi
2020-09-10 17:10 ` Jason Gunthorpe
2020-09-10 21:46 ` Benjamin Herrenschmidt
2020-09-10 23:29 ` Jason Gunthorpe
2020-09-11 0:39 ` Benjamin Herrenschmidt
2020-09-11 14:21 ` Jason Gunthorpe
2020-09-11 21:42 ` Clint Sbisa
2020-09-14 14:17 ` Jason Gunthorpe
2020-09-14 14:24 ` Clint Sbisa
2020-09-14 14:38 ` Jason Gunthorpe
2020-09-14 21:42 ` Benjamin Herrenschmidt
2020-09-14 22:00 ` Benjamin Herrenschmidt
2020-09-14 22:32 ` Clint Sbisa
2020-09-14 22:57 ` Jason Gunthorpe
2020-09-14 23:25 ` Benjamin Herrenschmidt
2020-09-15 10:18 ` Lorenzo Pieralisi
2020-09-15 11:05 ` Jason Gunthorpe
2020-09-15 23:17 ` Benjamin Herrenschmidt
2020-09-15 23:40 ` Jason Gunthorpe
2020-09-16 7:59 ` Benjamin Herrenschmidt
2020-09-16 12:12 ` Jason Gunthorpe
2020-09-16 14:09 ` Lorenzo Pieralisi
2020-09-16 14:14 ` Jason Gunthorpe
2020-09-16 23:59 ` Benjamin Herrenschmidt
2020-09-17 10:28 ` Lorenzo Pieralisi
2020-09-17 11:32 ` Jason Gunthorpe
2020-09-17 14:01 ` Lorenzo Pieralisi
2020-09-17 16:08 ` Will Deacon
2020-09-16 12:48 ` Leon Romanovsky
2020-09-16 8:33 ` Will Deacon
2020-09-16 8:48 ` Catalin Marinas
2020-09-16 14:15 ` Lorenzo Pieralisi
2020-09-16 17:00 ` Catalin Marinas [this message]
2020-09-16 21:29 ` Benjamin Herrenschmidt
2020-09-16 12:08 ` Jason Gunthorpe
2020-09-15 23:00 ` Benjamin Herrenschmidt
2020-09-15 23:12 ` Clint Sbisa
2020-09-14 21:41 ` Benjamin Herrenschmidt
2020-08-21 15:51 Clint Sbisa
2020-08-27 14:41 ` Clint Sbisa
2020-08-31 15:22 ` Clint Sbisa
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