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From:   Atish Patra <atishp@atishpatra.org>
Date:   Mon, 20 Jun 2022 12:41:12 -0700
Message-ID: <CAOnJCUKmWcMT83jkJHX3J56uNeVvFMgudGSg_DWg9G_faBjGXQ@mail.gmail.com>
Subject: Re: [PATCH 1/4] of: also handle dma-noncoherent in of_dma_is_coherent()
To:     Heiko Stuebner <heiko@sntech.de>
Cc:     Palmer Dabbelt <palmer@dabbelt.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        linux-riscv <linux-riscv@lists.infradead.org>,
        "linux-kernel@vger.kernel.org List" <linux-kernel@vger.kernel.org>,
        Wei Fu <wefu@redhat.com>, Guo Ren <guoren@kernel.org>,
        Christoph Muellner <cmuellner@linux.com>,
        Philipp Tomsich <philipp.tomsich@vrull.eu>,
        Christoph Hellwig <hch@lst.de>,
        Samuel Holland <samuel@sholland.org>,
        Anup Patel <anup@brainfault.org>,
        Nick Kossifidis <mick@ics.forth.gr>,
        Rob Herring <robh+dt@kernel.org>, krzk+dt@kernel.org,
        devicetree <devicetree@vger.kernel.org>,
        Drew Fustini <drew@beagleboard.org>,
        Randy Dunlap <rdunlap@infradead.org>
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On Mon, Jun 20, 2022 at 11:11 AM Heiko Stuebner <heiko@sntech.de> wrote:
>
> 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@sntech.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@sntech.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.
>

Ahh. That's great. Thanks!

> [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
> > >
> >
> >
> >
>
>
>
>


-- 
Regards,
Atish