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

Nicolas Saenz Julienne
2019-09-25T14:53:07Z

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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@suse.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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From 26d51853c25c04c28dbc09061951a93c102dabcd Mon Sep 17 00:00:00 2001
From: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Date: Wed, 25 Sep 2019 16:26:57 +0200
Subject: [PATCH] of: device: do not bail of_dma_configure() when force_dma is
set

Some Xen devices call of_dma_configure() without an actual DT node in
order for it to set its 'dma_ops'. That's the original intent of
'force_dma', honor that behaviour.

Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
---
drivers/of/device.c | 2 --
1 file changed, 2 deletions(-)

diff --git a/drivers/of/device.c b/drivers/of/device.c
index a45261e21144..7bc00f72468f 100644
--- a/drivers/of/device.c
+++ b/drivers/of/device.c
@@ -100,8 +100,6 @@ int of_dma_configure(struct device *dev, struct device_node *parent, bool force_
np = dev->of_node;
if (!np)
np = parent;
- if (!np)
- return -ENODEV;

ret = of_dma_get_range(np, &dma_addr, &paddr, &size);
if (ret < 0) {
--
2.23.0

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