Re: [Xen-devel] [PATCH 00/11] of: Fix DMA configuration for non-DT masters

[Rob Herring <robh+dt@xxxxxxxxxx>]

On Tue, Sep 24, 2019 at 1:12 PM Nicolas Saenz Julienne
<nsaenzjulienne@xxxxxxx> wrote:
>
> Hi All,
> this series tries to address one of the issues blocking us from
> upstreaming Broadcom's STB PCIe controller[1]. Namely, the fact that
> devices not represented in DT which sit behind a PCI bus fail to get the
> bus' DMA addressing constraints.
>
> This is due to the fact that of_dma_configure() assumes it's receiving a
> DT node representing the device being configured, as opposed to the PCIe
> bridge node we currently pass. This causes the code to directly jump
> into PCI's parent node when checking for 'dma-ranges' and misses
> whatever was set there.
>
> To address this I create a new API in OF - inspired from Robin Murphys
> original proposal[2] - which accepts a bus DT node as it's input in
> order to configure a device's DMA constraints. The changes go deep into
> of/address.c's implementation, as a device being having a DT node
> assumption was pretty strong.
>
> On top of this work, I also cleaned up of_dma_configure() removing its
> redundant arguments and creating an alternative function for the special cases
> not applicable to either the above case or the default usage.
>
> IMO the resulting functions are more explicit. They will probably
> surface some hacky usages that can be properly fixed as I show with the
> DT fixes on the Layerscape platform.
>
> This was also tested on a Raspberry Pi 4 with a custom PCIe driver and
> on a Seattle AMD board.

Humm, I've been working on this issue too. Looks similar though yours
has a lot more churn and there's some other bugs I've found.

Can you test out this branch[1]. I don't have any h/w needing this,
but wrote a unittest and tested with modified QEMU.

Rob

[1] git://git.kernel.org/pub/scm/linux/kernel/git/robh/linux.git dma-masks

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