linux-kernel - Re: [PATCH 05/11] of: Ratify of_dma

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Date:   Mon, 30 Sep 2019 16:24:20 -0500
From:   Rob Herring <robh@...nel.org>
To:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
Cc:     Christoph Hellwig <hch@...radead.org>, devicetree@...r.kernel.org,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        Frank Rowand <frowand.list@...il.com>,
        PCI <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Marek Vasut <marek.vasut@...il.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Oza Pawandeep <oza.oza@...adcom.com>,
        Stefan Wahren <wahrenst@....net>,
        Simon Horman <horms+renesas@...ge.net.au>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH 05/11] of: Ratify of_dma_configure() interface

On Mon, Sep 30, 2019 at 8:32 AM Nicolas Saenz Julienne
<nsaenzjulienne@...e.de> wrote:
>
> On Mon, 2019-09-30 at 05:57 -0700, Christoph Hellwig wrote:
> > On Thu, Sep 26, 2019 at 07:24:49PM -0500, Rob Herring wrote:
> > > -int of_dma_configure(struct device *dev, struct device_node *np, bool
> > > force_dma)
> > > +int of_dma_configure(struct device *dev, struct device_node *parent, bool
> > > force_dma)
> >
> > This creates a > 80 char line.
> >
> > >  {
> > >     u64 dma_addr, paddr, size = 0;
> > >     int ret;
> > >     bool coherent;
> > >     unsigned long offset;
> > >     const struct iommu_ops *iommu;
> > > +   struct device_node *np;
> > >     u64 mask;
> > >
> > > +   np = dev->of_node;
> > > +   if (!np)
> > > +           np = parent;
> > > +   if (!np)
> > > +           return -ENODEV;
> >
> > I have to say I find the older calling convention simpler to understand.
> > If we want to enforce the invariant I'd rather do that explicitly:
> >
> >       if (dev->of_node && np != dev->of_node)
> >               return -EINVAL;
>
> As is, this would break Freescale Layerscape fsl-mc bus' dma_configure():

This may break PCI too for devices that have a DT node.

> static int fsl_mc_dma_configure(struct device *dev)
> {
>         struct device *dma_dev = dev;
>
>         while (dev_is_fsl_mc(dma_dev))
>                 dma_dev = dma_dev->parent;
>
>         return of_dma_configure(dev, dma_dev->of_node, 0);
> }
>
> But I think that with this series, given the fact that we now treat the lack of
> dma-ranges as a 1:1 mapping instead of an error, we could rewrite the function
> like this:

Now, I'm reconsidering allowing this abuse... It's better if the code
which understands the bus structure in DT for a specific bus passes in
the right thing. Maybe I should go back to Robin's version (below).
OTOH, the existing assumption that 'dma-ranges' was in the immediate
parent was an assumption on the bus structure which maybe doesn't
always apply.

diff --git a/drivers/of/device.c b/drivers/of/device.c
index a45261e21144..6951450bb8f3 100644
--- a/drivers/of/device.c
+++ b/drivers/of/device.c
@@ -98,12 +98,15 @@ int of_dma_configure(struct device *dev, struct
device_node *parent, bool force_
        u64 mask;

        np = dev->of_node;
-       if (!np)
-               np = parent;
+       if (np)
+               parent = of_get_dma_parent(np);
+       else
+               np = of_node_get(parent);
        if (!np)
                return -ENODEV;

-       ret = of_dma_get_range(np, &dma_addr, &paddr, &size);
+       ret = of_dma_get_range(parent, &dma_addr, &paddr, &size);
+       of_node_put(parent);
        if (ret < 0) {
                /*
                 * For legacy reasons, we have to assume some devices need