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From: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>, jgg@nvidia.com
Cc: Leon Romanovsky <leon@kernel.org>,
	linux-pci@vger.kernel.org, Bjorn Helgaas <helgaas@kernel.org>,
	catalin.marinas@arm.com, 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: Thu, 10 Sep 2020 10:46:00 +0100	[thread overview]
Message-ID: <20200910094600.GA22840@e121166-lin.cambridge.arm.com> (raw)
In-Reply-To: <28d333afc73bd854390f8c39691a735040ba5b39.camel@kernel.crashing.org>

[+Jason]

On Tue, Sep 08, 2020 at 09:33:42AM +1000, Benjamin Herrenschmidt wrote:
> On Thu, 2020-09-03 at 12:08 +0100, Lorenzo Pieralisi wrote:
> > > 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.
> > 
> > Minus what I wrote above, I agree with you. I'd still be able to
> > understand what this patch changes in the mellanox driver HW
> > handling though - not sure what they expect from
> > arch_can_pci_mmap_wc()
> > returning 1.
> 
> I don't know enough to get into the finer details but looking a bit it
> seems when this is set, they allow extra ioctls to create buffers
> mapped with pgprot_writecombine().
> 
> I suppose this means faster MMIO backet buffers for small packets (ie,
> non-DMA use case).
> 
> Also note that mlx5_ib_test_wc() only uses arch_can_pci_mmap_wc() for a
> non-ROCE ethernet port on a PF... For anyting else, it just seems to
> actually try to do it and see what happens :-)
> 
> Leon: Can you clarify the use of arch_can_pci_mmap_wc() in mlx5 and
> whether you see an issue with enabling this on arm64 ?

Hi Jason,

I was wondering if you could help us with this question, we are trying
to understand what enabling arch_can_pci_mmap_wc() on arm64 would cause
in mellanox drivers wrt mappings and whether there is an expected
behaviour behind them, in particular whether there is an implicit
reliance on x86 write-combine arch/interconnect details.

Thanks,
Lorenzo

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  reply	other threads:[~2020-09-10  9:47 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 [this message]
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
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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