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Message-ID: <9bc396116372de5b538d71d8f9ae9c3259f1002e.camel@suse.de>
Subject: Re: [PATCH stable v5.10 0/7] arm64: Default to 32-bit wide ZONE_DMA
From:   Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
To:     Greg KH <gregkh@linuxfoundation.org>,
        Jing Xiangfeng <jingxiangfeng@huawei.com>
Cc:     catalin.marinas@arm.com, will@kernel.org,
        akpm@linux-foundation.org, paul.walmsley@sifive.com,
        palmer@dabbelt.com, aou@eecs.berkeley.edu, rppt@kernel.org,
        lorenzo.pieralisi@arm.com, guohanjun@huawei.com,
        sudeep.holla@arm.com, rjw@rjwysocki.net, lenb@kernel.org,
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        anshuman.khandual@arm.com, bhelgaas@google.com, guro@fb.com,
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        wangkefeng.wang@huawei.com
Date:   Thu, 04 Mar 2021 15:05:32 +0100
In-Reply-To: <YEDkmj6cchMPAq2h@kroah.com>
References: <20210303073319.2215839-1-jingxiangfeng@huawei.com>
         <YEDkmj6cchMPAq2h@kroah.com>
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Hi Greg.

On Thu, 2021-03-04 at 14:46 +0100, Greg KH wrote:
> On Wed, Mar 03, 2021 at 03:33:12PM +0800, Jing Xiangfeng wrote:
> > Using two distinct DMA zones turned out to be problematic. Here's an
> > attempt go back to a saner default.
>=20
> What problem does this solve?  How does this fit into the stable kernel
> rules?

We changed the way we setup memory zones in arm64 in order to cater for
Raspberry Pi 4's weird DMA constraints: ZONE_DMA spans the lower 1GB of mem=
ory
and ZONE_DMA32 the rest of the 32bit address space. Since you can't allocat=
e
memory that crosses zone boundaries, this broke crashkernel allocations on =
big
machines. This series fixes all this by parsing the HW description and chec=
king
for DMA constrained buses. When not found, the unnecessary zone creation is
skipped.

That said, I have no clue whether this falls or not into the stable kernel
rules.

Regards,
Nicolas


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