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

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Message-ID: <d1a31a2ec8eb2f226b1fb41f6c24ffb47c3bf7c7.camel@suse.de>
Date:   Wed, 25 Sep 2019 16:52:59 +0200
From:   Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     devicetree@...r.kernel.org, Frank Rowand <frowand.list@...il.com>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        linux-wireless <linux-wireless@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        "open list:DMA GENERIC OFFLOAD ENGINE SUBSYSTEM" 
        <dmaengine@...r.kernel.org>, etnaviv@...ts.freedesktop.org,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        xen-devel@...ts.xenproject.org, linux-tegra@...r.kernel.org,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        linux-pci@...r.kernel.org, Matthias Brugger <mbrugger@...e.com>,
        Robin Murphy <robin.murphy@....com>,
        Florian Fainelli <f.fainelli@...il.com>,
        james.quinlan@...adcom.com, Stefan Wahren <wahrenst@....net>,
        Dan Williams <dan.j.williams@...el.com>,
        freedreno <freedreno@...ts.freedesktop.org>
Subject: Re: [PATCH 00/11] of: Fix DMA configuration for non-DT masters

On Tue, 2019-09-24 at 16:59 -0500, Rob Herring wrote:
> On Tue, Sep 24, 2019 at 1:12 PM Nicolas Saenz Julienne
> <nsaenzjulienne@...e.de> 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.

That's good news, and yes now that I see it, some stuff on my series is overly
complicated. Specially around of_translate_*().

On top of that, you removed in of_dma_get_range():

-	/*
-	 * At least empty ranges has to be defined for parent node if
-	 * DMA is supported
-	 */
-	if (!ranges)
-		break;

Which I assumed was bound to the standard and makes things easier.

> 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.

I reviewed everything, I did find a minor issue, see the patch attached.

Also I tested your branch both on an RPi4, with a PCI device that depends on
these changes and by comparing the OF debugs logs on a Layerscape board which
uses dma-ranges, dma-coherent and IOMMU. All works as expected.

Will you send this series for v5.5? Please keep me in the loop, I'll review and
test the final version.

Regards,
Nicolas


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