linux-kernel - Re: [RFC PATCH 3/3] of: fix node traversing in of_dma_get

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Date:   Mon, 27 Mar 2017 15:45:05 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Rob Herring <robh@...nel.org>, Oza Pawandeep <oza.oza@...adcom.com>
Cc:     Joerg Roedel <joro@...tes.org>,
        Linux IOMMU <iommu@...ts.linux-foundation.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "bcm-kernel-feedback-list@...adcom.com" 
        <bcm-kernel-feedback-list@...adcom.com>
Subject: Re: [RFC PATCH 3/3] of: fix node traversing in of_dma_get_range

Hi Rob,

On 27/03/17 15:34, Rob Herring wrote:
> On Sat, Mar 25, 2017 at 12:31 AM, Oza Pawandeep <oza.oza@...adcom.com> wrote:
>> it jumps to the parent node without examining the child node.
>> also with that, it throws "no dma-ranges found for node"
>> for pci dma-ranges.
>>
>> this patch fixes device node traversing for dma-ranges.
> 
> What's the DT look like that doesn't work?

The problem is the bodge in pci_dma_configure() where we don't have an
OF node for the actual device itself, so pass in the host bridge's OF
node instead. This happens to work well enough for dma-coherent, but I
don't think dma-ranges was even considered at the time.

As it happens I'm currently halfway through writing an experiment
wherein pci_dma_configure() creates a temporary child node for the
of_dma_configure() call if no other suitable alternative (e.g. some
intermediate bridge node) exists. How hard are you likely to NAK that
approach? ;)

> dma-ranges is supposed to be a bus property, not a device's property.
> So looking at the parent is correct behavior generally.

Indeed, this patch as-is will break currently correct DTs (because we
won't find dma-ranges on the device, so will bail before even looking at
the parent as we should).

Robin.

> 
> Rob
>