linux-kernel - Re: [PATCH v3 3/3] mmc: xenon: Fix 2G limitation on AC5 SoC

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Message-ID: <CACRpkdZhjrze4q39SPjATESRCQ_RW4XJn1a1SMDy-hApXu9VEg@mail.gmail.com>
Date:   Tue, 13 Dec 2022 10:16:57 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Vadym Kochan <vadym.kochan@...ision.eu>,
        Hu Ziji <huziji@...vell.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        linux-mmc@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, Elad Nachman <enachman@...vell.com>,
        Chris Packham <chris.packham@...iedtelesis.co.nz>
Subject: Re: [PATCH v3 3/3] mmc: xenon: Fix 2G limitation on AC5 SoC

On Mon, Dec 12, 2022 at 9:43 AM Adrian Hunter <adrian.hunter@...el.com> wrote:

> >> Right but I guess I meant what about 0x3_00000000..0x3_ffffffff ?
> >> Isn't that also in DMA_BIT_MASK(34)
> >
> > Yes, you are right.
>
> So it would fail in that case?  Is it possible to use devicetree
> reserved memory or some such, to set aside 64k for the bounce
> buffer DMA mapping?

Yups spot on, reserved-memory can be used along with the kernel
CONFIG_DMA_CMA to achieve exactly this:
Documentation/devicetree/bindings/reserved-memory/reserved-memory.yaml
kernel/dma/Kconfig

Yours,
Linus Walleij