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

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Message-ID: <CAOnJCUJC3dk21cYXXDOsamvwFDHsukoBx7HEYwqHM+MN5fLRpA@mail.gmail.com>
Date:   Mon, 20 Jun 2022 09:33:09 -0700
From:   Atish Patra <atishp@...shpatra.org>
To:     Heiko Stuebner <heiko@...ech.de>
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()

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 ?

>   */
>  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