From: Christoph Hellwig <hch@infradead.org>
To: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Cc: devicetree <devicetree@vger.kernel.org>,
Florian Fainelli <f.fainelli@gmail.com>,
Rob Herring <robh@kernel.org>,
linux-pci <linux-pci@vger.kernel.org>,
Neil Armstrong <narmstrong@baylibre.com>,
Christoph Hellwig <hch@infradead.org>,
Bjorn Helgaas <helgaas@kernel.org>,
linux-rpi-kernel <linux-rpi-kernel@lists.infradead.org>,
bcm-kernel-feedback-list <bcm-kernel-feedback-list@broadcom.com>,
Robin Murphy <robin.murphy@arm.com>,
linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
Robin Murphy <robin.murphy@arm.con>
Subject: Re: RPi4 can't deal with 64 bit PCI accesses
Date: Fri, 26 Feb 2021 05:32:23 +0000 [thread overview]
Message-ID: <20210226053223.GA2763268@infradead.org> (raw)
In-Reply-To: <01091991523dac4c0c7e40f40e95c887af84f560.camel@suse.de>
On Thu, Feb 25, 2021 at 12:35:27PM +0100, Nicolas Saenz Julienne wrote:
> Yes, that's what I had in mind myself. All in all, why penalize the rest of
> busses in the system. What I'm planning is to introduce a '64bit-mmio-broken'
> DT property that'll utimately live somwhere in 'struct device.'
>
> WRT why not defaulting to 32-bit accesses for distro images if they support
> RPi4. My *un-educated* guess is that, the performance penalty of checking for a
> device flag is (way) lower than having to resort to two distinct write
> operations with their assorted memory barriers. I'm sure you can
> comment/correct me here.
Various high performance devices rely on the fact that 64-bit MMIO
writes are atomic, and will have to use an extra lock and/or an entirely
different programming model if they are not supported.
If that is not the case just using 32-bit accesses always is certainly
easier, that's what we did for the slow-path only 64-bit registers in
NVMe.
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next prev parent reply other threads:[~2021-02-26 5:33 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-22 15:47 RPi4 can't deal with 64 bit PCI accesses Nicolas Saenz Julienne
2021-02-22 16:18 ` Ard Biesheuvel
2021-02-22 16:36 ` Nicolas Saenz Julienne
2021-02-22 16:56 ` Robin Murphy
2021-02-24 16:55 ` Florian Fainelli
2021-02-24 20:25 ` Christoph Hellwig
2021-02-24 20:35 ` Florian Fainelli
2021-02-25 10:29 ` Neil Armstrong
2021-02-25 11:10 ` Robin Murphy
2021-02-25 11:35 ` Nicolas Saenz Julienne
2021-02-26 5:32 ` Christoph Hellwig [this message]
2021-02-25 10:41 ` David Woodhouse
2021-02-22 17:55 ` Russell King - ARM Linux admin
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