From: Christoph Hellwig <hch@infradead.org>
To: Florian Fainelli <f.fainelli@gmail.com>
Cc: devicetree <devicetree@vger.kernel.org>,
Rob Herring <robh@kernel.org>,
linux-pci <linux-pci@vger.kernel.org>,
Bjorn Helgaas <helgaas@kernel.org>,
Nicolas Saenz Julienne <nsaenzjulienne@suse.de>,
bcm-kernel-feedback-list <bcm-kernel-feedback-list@broadcom.com>,
Robin Murphy <robin.murphy@arm.con>,
Robin Murphy <robin.murphy@arm.com>,
linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
linux-rpi-kernel <linux-rpi-kernel@lists.infradead.org>
Subject: Re: RPi4 can't deal with 64 bit PCI accesses
Date: Wed, 24 Feb 2021 20:25:38 +0000 [thread overview]
Message-ID: <20210224202538.GA2346950@infradead.org> (raw)
In-Reply-To: <6088038a-2366-2f63-0678-c65a0d2efabd@gmail.com>
On Wed, Feb 24, 2021 at 08:55:10AM -0800, Florian Fainelli wrote:
> > Working around kernel I/O accessors is all very well, but another
> > concern for PCI in particular is when things like framebuffer memory can
> > get mmap'ed into userspace (or even memremap'ed within the kernel). Even
> > in AArch32, compiled code may result in 64-bit accesses being generated
> > depending on how the CPU and interconnect handle LDRD/STRD/LDM/STM/etc.,
> > so it's basically not safe to ever let that happen at all.
>
> Agreed, this makes finding a generic solution a tiny bit harder. Do you
> have something in mind Nicolas?
The only workable solution is a new
bool 64bit_mmio_supported(void)
check that is used like:
if (64bit_mmio_supported())
readq(foodev->regs, REG_OFFSET);
else
lo_hi_readq(foodev->regs, REG_OFFSET);
where 64bit_mmio_supported() return false for all 32-bit kernels,
true for all non-broken 64-bit kernels and is an actual function
for arm64 multiplatforms builds that include te RPi quirk.
The above would then replace the existing magic from the
<linux/io-64-nonatomic-lo-hi.h> and <linux/io-64-nonatomic-hi-lo.h>
headers.
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next prev parent reply other threads:[~2021-02-24 20:27 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 [this message]
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
2021-02-25 10:41 ` David Woodhouse
2021-02-22 17:55 ` Russell King - ARM Linux admin
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