From: Ard Biesheuvel <ardb@kernel.org>
To: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Cc: Christoph Hellwig <hch@lst.de>,
"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
<devicetree@vger.kernel.org>,
Frank Rowand <frowand.list@gmail.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux Memory Management List <linux-mm@kvack.org>,
iommu@lists.linux-foundation.org,
Rob Herring <robh+dt@kernel.org>,
linux-rpi-kernel@lists.infradead.org,
Will Deacon <will@kernel.org>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Robin Murphy <robin.murphy@arm.com>
Subject: Re: [PATCH 1/4] of/fdt: Update zone_dma_bits when running in bcm2711
Date: Fri, 9 Oct 2020 11:13:59 +0200 [thread overview]
Message-ID: <CAMj1kXGP_OTKgqMT0-+t3=7EKDY26y9n9xjLodSF1E-mUCe9tg@mail.gmail.com> (raw)
In-Reply-To: <513833810c15b5efeab7c3cbae1963a78c71a79f.camel@suse.de>
On Fri, 9 Oct 2020 at 10:36, Nicolas Saenz Julienne
<nsaenzjulienne@suse.de> wrote:
>
> On Fri, 2020-10-09 at 09:37 +0200, Ard Biesheuvel wrote:
> > On Fri, 9 Oct 2020 at 09:11, Christoph Hellwig <hch@lst.de> wrote:
> > > On Thu, Oct 08, 2020 at 12:05:25PM +0200, Nicolas Saenz Julienne wrote:
> > > > Sadly I just realised that the series is incomplete, we have RPi4 users that
> > > > want to boot unsing ACPI, and this series would break things for them. I'll
> > > > have a word with them to see what we can do for their use-case.
> > >
> > > Stupid question: why do these users insist on a totally unsuitable
> > > interface? And why would we as Linux developers care to support such
> > > a aims?
> >
> > The point is really whether we want to revert changes in Linux that
> > made both DT and ACPI boot work without quirks on RPi4.
>
> Well, and broke a big amount of devices that were otherwise fine.
>
Yeah that was unfortunate.
> > Having to check the RPi4 compatible string or OEM id in core init code is
> > awful, regardless of whether you boot via ACPI or via DT.
> >
> > The problem with this hardware is that it uses a DMA mask which is
> > narrower than 32, and the arm64 kernel is simply not set up to deal
> > with that at all. On DT, we have DMA ranges properties and the likes
> > to describe such limitations, on ACPI we have _DMA methods as well as
> > DMA range attributes in the IORT, both of which are now handled
> > correctly. So all the information is there, we just have to figure out
> > how to consume it early on.
>
> Is it worth the effort just for a single board? I don't know about ACPI but
> parsing dma-ranges that early at boot time is not trivial. My intuition tells
> me that it'd be even harder for ACPI, being a more complex data structure.
>
Yes, it will be harder, especially for the _DMA methods.
> > Interestingly, this limitation always existed in the SoC, but it
> > wasn't until they started shipping it with more than 1 GB of DRAM that
> > it became a problem. This means issues like this could resurface in
> > the future with existing SoCs when they get shipped with more memory,
> > and so I would prefer fixing this in a generic way.
>
> Actually what I proposed here is pretty generic. Specially from arm64's
> perspective. We call early_init_dt_scan(), which sets up zone_dma_bits based on
> whatever it finds in DT. Both those operations are architecture independent.
> arm64 arch code doesn't care about the logic involved in ascertaining
> zone_dma_bits. I get that the last step isn't generic. But it's all setup so as
> to make it as such whenever it's worth the effort.
>
The problem is that, while we are providing a full description of the
SoC's capabilities, we short circuit this by inserting knowledge into
the code (that is shared between all DT architectures) that
"brcm,bcm2711" is special, and needs a DMA zone override.
I think for ACPI boot, we might be able to work around this by cold
plugging the memory above 1 GB, but I have to double check whether it
won't get pulled into ZONE_DMA32 anyway (unless anyone can answer that
for me here from the top of their head)
next prev parent reply other threads:[~2020-10-09 9:14 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-01 16:17 [PATCH 0/4] arm64: Default to 32-bit wide ZONE_DMA Nicolas Saenz Julienne
2020-10-01 16:17 ` [PATCH 1/4] of/fdt: Update zone_dma_bits when running in bcm2711 Nicolas Saenz Julienne
2020-10-01 17:15 ` Catalin Marinas
2020-10-01 17:23 ` Catalin Marinas
2020-10-01 17:31 ` Nicolas Saenz Julienne
2020-10-01 20:02 ` Rob Herring
2020-10-02 11:55 ` Catalin Marinas
2020-10-08 10:05 ` Nicolas Saenz Julienne
2020-10-08 10:13 ` Catalin Marinas
2020-10-08 19:43 ` Ard Biesheuvel
2020-10-09 3:59 ` Jeremy Linton
2020-10-09 8:37 ` Nicolas Saenz Julienne
2020-10-09 7:10 ` Christoph Hellwig
2020-10-09 7:37 ` Ard Biesheuvel
2020-10-09 8:36 ` Nicolas Saenz Julienne
2020-10-09 9:13 ` Ard Biesheuvel [this message]
2020-10-09 13:33 ` Nicolas Saenz Julienne
2020-10-09 15:24 ` Lorenzo Pieralisi
2020-10-09 16:23 ` Ard Biesheuvel
2020-10-09 17:10 ` Catalin Marinas
2020-10-10 10:36 ` Ard Biesheuvel
2020-10-10 10:53 ` Nicolas Saenz Julienne
2020-10-10 12:38 ` Catalin Marinas
2020-10-12 6:47 ` Christoph Hellwig
2020-10-12 8:47 ` Catalin Marinas
2020-10-02 9:05 ` kernel test robot
2020-10-01 16:17 ` [PATCH 2/4] dma-direct: Turn zone_dma_bits default value into a define Nicolas Saenz Julienne
2020-10-01 16:17 ` [PATCH 3/4] arm64: Default to 32-bit ZONE_DMA Nicolas Saenz Julienne
2020-10-01 17:19 ` Catalin Marinas
2020-10-01 16:17 ` [PATCH 4/4] mm: Update DMA zones description Nicolas Saenz Julienne
2020-10-01 17:19 ` Catalin Marinas
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