Re: [PATCH] of: Add OF_DMA_DEFAULT_COHERENT & select it on powerpc

[Ulf Hansson]

On Sun, 26 Jan 2020 at 12:53, Michael Ellerman <mpe@xxxxxxxxxxxxxx> wrote:
>
> There's an OF helper called of_dma_is_coherent(), which checks if a
> device has a "dma-coherent" property to see if the device is coherent
> for DMA.
>
> But on some platforms devices are coherent by default, and on some
> platforms it's not possible to update existing device trees to add the
> "dma-coherent" property.
>
> So add a Kconfig symbol to allow arch code to tell
> of_dma_is_coherent() that devices are coherent by default, regardless
> of the presence of the property.
>
> Select that symbol on powerpc when NOT_COHERENT_CACHE is not set, ie.
> when the system has a coherent cache.
>
> Fixes: 92ea637edea3 ("of: introduce of_dma_is_coherent() helper")
> Cc: stable@xxxxxxxxxxxxxxx # v3.16+
> Reported-by: Christian Zigotzky <chzigotzky@xxxxxxxxxxx>
> Tested-by: Christian Zigotzky <chzigotzky@xxxxxxxxxxx>
> Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>

Thanks Michael for helping out fixing and this! The patch looks good to me.

Reviewed-by: Ulf Hansson <ulf.hansson@xxxxxxxxxx>

Kind regards
Uffe

> ---
>  arch/powerpc/Kconfig | 1 +
>  drivers/of/Kconfig   | 4 ++++
>  drivers/of/address.c | 6 +++++-
>  3 files changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 1ec34e16ed65..19f5aa8ac9a3 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -238,6 +238,7 @@ config PPC
>         select NEED_DMA_MAP_STATE               if PPC64 || NOT_COHERENT_CACHE
>         select NEED_SG_DMA_LENGTH
>         select OF
> +       select OF_DMA_DEFAULT_COHERENT          if !NOT_COHERENT_CACHE
>         select OF_EARLY_FLATTREE
>         select OLD_SIGACTION                    if PPC32
>         select OLD_SIGSUSPEND
> diff --git a/drivers/of/Kconfig b/drivers/of/Kconfig
> index 37c2ccbefecd..d91618641be6 100644
> --- a/drivers/of/Kconfig
> +++ b/drivers/of/Kconfig
> @@ -103,4 +103,8 @@ config OF_OVERLAY
>  config OF_NUMA
>         bool
>
> +config OF_DMA_DEFAULT_COHERENT
> +       # arches should select this if DMA is coherent by default for OF devices
> +       bool
> +
>  endif # OF
> diff --git a/drivers/of/address.c b/drivers/of/address.c
> index 99c1b8058559..e8a39c3ec4d4 100644
> --- a/drivers/of/address.c
> +++ b/drivers/of/address.c
> @@ -995,12 +995,16 @@ int of_dma_get_range(struct device_node *np, u64 *dma_addr, u64 *paddr, u64 *siz
>   * @np:        device node
>   *
>   * It returns true if "dma-coherent" property was found
> - * for this device in DT.
> + * for this device in the DT, or if DMA is coherent by
> + * default for OF devices on the current platform.
>   */
>  bool of_dma_is_coherent(struct device_node *np)
>  {
>         struct device_node *node = of_node_get(np);
>
> +       if (IS_ENABLED(CONFIG_OF_DMA_DEFAULT_COHERENT))
> +               return true;
> +
>         while (node) {
>                 if (of_property_read_bool(node, "dma-coherent")) {
>                         of_node_put(node);
> --
> 2.21.1
>