[v6,1/4] of: also handle dma-noncoherent in of_dma_is_coherent()

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.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
---
 drivers/of/address.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

Reviewed-by: Guo Ren <guoren@kernel.org>

On Wed, Jul 6, 2022 at 6:47 AM 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.
>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Rob Herring <robh@kernel.org>
> Signed-off-by: Heiko Stuebner <heiko@sntech.de>
> ---
>  drivers/of/address.c | 17 ++++++++++-------
>  1 file changed, 10 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/of/address.c b/drivers/of/address.c
> index 94f017d808c4..96f0a12e507c 100644
> --- a/drivers/of/address.c
> +++ b/drivers/of/address.c
> @@ -1045,26 +1045,29 @@ 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.
>   */
>  bool of_dma_is_coherent(struct device_node *np)
>  {
>         struct device_node *node;
> -
> -       if (IS_ENABLED(CONFIG_OF_DMA_DEFAULT_COHERENT))
> -               return true;
> +       bool is_coherent = IS_ENABLED(CONFIG_OF_DMA_DEFAULT_COHERENT);
>
>         node = of_node_get(np);
>
>         while (node) {
>                 if (of_property_read_bool(node, "dma-coherent")) {
> -                       of_node_put(node);
> -                       return true;
> +                       is_coherent = true;
> +                       break;
> +               }
> +               if (of_property_read_bool(node, "dma-noncoherent")) {
> +                       is_coherent = false;
> +                       break;
>                 }
>                 node = of_get_next_dma_parent(node);
>         }
>         of_node_put(node);
> -       return false;
> +       return is_coherent;
>  }
>  EXPORT_SYMBOL_GPL(of_dma_is_coherent);
>
> --
> 2.35.1
>