linux-kernel - Re: [PATCH 1/4] of: also handle dma-noncoherent in of_dma_is

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Message-ID: <5907887.LM0AJKV5NW@phil>
Date:   Mon, 20 Jun 2022 20:11:06 +0200
From:   Heiko Stuebner <heiko@...ech.de>
To:     Atish Patra <atishp@...shpatra.org>
Cc:     Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        Wei Fu <wefu@...hat.com>, Guo Ren <guoren@...nel.org>,
        Christoph Muellner <cmuellner@...ux.com>,
        Philipp Tomsich <philipp.tomsich@...ll.eu>,
        Christoph Hellwig <hch@....de>,
        Samuel Holland <samuel@...lland.org>,
        Anup Patel <anup@...infault.org>,
        Nick Kossifidis <mick@....forth.gr>,
        Rob Herring <robh+dt@...nel.org>, krzk+dt@...nel.org,
        devicetree <devicetree@...r.kernel.org>,
        Drew Fustini <drew@...gleboard.org>,
        Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH 1/4] of: also handle dma-noncoherent in of_dma_is_coherent()

Hi Atish,

Am Montag, 20. Juni 2022, 18:33:09 CEST schrieb Atish Patra:
> On Sun, Jun 19, 2022 at 1:32 PM Heiko Stuebner <heiko@...ech.de> wrote:
> >
> > of_dma_is_coherent() currently expects the architecture to be
> > non-coherent and some devices being coherent getting marked
> > as such with the dma-coherent devicetree property.
> >
> > For PowerPC CONFIG_OF_DMA_DEFAULT_COHERENT was added which currently
> > makes of_dma_is_coherent() always return true but doesn't handle
> > the case of the architecture being coherent but some devices not.
> >
> > So modify the function to also check for dma-noncoherent and
> > set a suitable default return value. If CONFIG_OF_DMA_DEFAULT_COHERENT
> > is set the value starts with true and finding dma-noncoherent will
> > set it to false and without CONFIG_OF_DMA_DEFAULT_COHERENT, the
> > behaviour is reversed.
> >
> > Signed-off-by: Heiko Stuebner <heiko@...ech.de>
> > ---
> >  drivers/of/address.c | 16 +++++++++++-----
> >  1 file changed, 11 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/of/address.c b/drivers/of/address.c
> > index 94f017d808c4..1c362d09983d 100644
> > --- a/drivers/of/address.c
> > +++ b/drivers/of/address.c
> > @@ -1045,26 +1045,32 @@ phys_addr_t __init of_dma_get_max_cpu_address(struct device_node *np)
> >   *
> >   * It returns true if "dma-coherent" property was found
> >   * for this device in the DT, or if DMA is coherent by
> > - * default for OF devices on the current platform.
> > + * default for OF devices on the current platform and no
> > + * "dma-noncoherent" property was found for this device.
> 
> "dma-noncoherent" is not a standard DT property. I couldn't find any
> references to
> it in the kernel as well. If we are introducing a new DT property for
> non-coherent devices,
> it should be added in DT bindings as well ?

The dma-coherent is part of the core devicetree-spec,
so I sent a patch adding dma-noncoherent [0]
to the devicetree-spec mailing list yesterday as well.

[0] https://www.spinics.net/lists/devicetree-spec/msg01053.html


> 
> >   */
> >  bool of_dma_is_coherent(struct device_node *np)
> >  {
> >         struct device_node *node;
> > +       bool ret = false;
> >
> >         if (IS_ENABLED(CONFIG_OF_DMA_DEFAULT_COHERENT))
> > -               return true;
> > +               ret = true;
> >
> >         node = of_node_get(np);
> >
> >         while (node) {
> >                 if (of_property_read_bool(node, "dma-coherent")) {
> > -                       of_node_put(node);
> > -                       return true;
> > +                       ret = true;
> > +                       break;
> > +               }
> > +               if (of_property_read_bool(node, "dma-noncoherent")) {
> > +                       ret = false;
> > +                       break;
> >                 }
> >                 node = of_get_next_dma_parent(node);
> >         }
> >         of_node_put(node);
> > -       return false;
> > +       return ret;
> >  }
> >  EXPORT_SYMBOL_GPL(of_dma_is_coherent);
> >
> > --
> > 2.35.1
> >
> 
> 
>