Re: [PATCH] arm64: dts: renesas: Add /soc dma-ranges

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On Sat, Sep 7, 2019 at 5:16 PM <marek.vasut@xxxxxxxxx> wrote:
>
> From: Marek Vasut <marek.vasut+renesas@xxxxxxxxx>
>
> Add dma-ranges property into /soc node to describe the DMA capabilities
> of the bus. This is currently needed to translate PCI DMA ranges, which
> are limited to 32bit addresses.

FYI, I've started working on this problem and issues around
dma-ranges/dma_mask. Hopefully I'll get some patches out next week.

> Signed-off-by: Marek Vasut <marek.vasut+renesas@xxxxxxxxx>
> Cc: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
> Cc: Wolfram Sang <wsa@xxxxxxxxxxxxx>
> Cc: devicetree@xxxxxxxxxxxxxxx
> Cc: linux-renesas-soc@xxxxxxxxxxxxxxx
> To: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> ---
> NOTE: This is needed for the following patches to work correctly:
>       https://patchwork.ozlabs.org/patch/1144870/
>       https://patchwork.ozlabs.org/patch/1144871/

First I'm seeing those... Well, I do have v7 from 2+ years ago...

Not sure if these take into account the new dma_bus_mask, but that
should simplify solving the issue.

> ---
>  arch/arm64/boot/dts/renesas/r8a7795.dtsi  | 1 +
>  arch/arm64/boot/dts/renesas/r8a7796.dtsi  | 1 +
>  arch/arm64/boot/dts/renesas/r8a77965.dtsi | 1 +
>  3 files changed, 3 insertions(+)
>
> diff --git a/arch/arm64/boot/dts/renesas/r8a7795.dtsi b/arch/arm64/boot/dts/renesas/r8a7795.dtsi
> index 95deff66eeb6..2102140a6723 100644
> --- a/arch/arm64/boot/dts/renesas/r8a7795.dtsi
> +++ b/arch/arm64/boot/dts/renesas/r8a7795.dtsi
> @@ -330,6 +330,7 @@
>                 #address-cells = <2>;
>                 #size-cells = <2>;
>                 ranges;
> +               dma-ranges = <0 0x40000000 0 0x40000000 0 0xc0000000>;

Is the limitation in the bus or the PCI bridge or both? The commit
message sounds like it's the PCI bridge in which case this is wrong
(or incomplete). 'dma-ranges' should be on the bus node where the
restriction/translation exists. For PCI devices, that's the PCI bridge
node. So a 32-bit only PCI bridge should have a dma-ranges size of
4GB. If the SoC bus has more restrictions, then that should be in the
PCI bridge parent assuming that restriction also applies to other
devices.

Rob



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