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    SubjectRe: [PATCH V5 1/9] ACPI: Honor ACPI _CCA attribute setting
    On Thu, Oct 29, 2015 at 6:50 AM, Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com> wrote:
    > From: Jeremy Linton <jeremy.linton@arm.com>
    >
    > ACPI configurations can now mark devices as noncoherent,
    > support that choice.
    >
    > NOTE: This is required to support USB on ARM Juno Development Board.
    >
    > Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
    > Signed-off-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>
    > CC: Bjorn Helgaas <bhelgaas@google.com>
    > CC: Catalin Marinas <catalin.marinas@arm.com>
    > CC: Rob Herring <robh+dt@kernel.org>
    > CC: Will Deacon <will.deacon@arm.com>
    > CC: Rafael J. Wysocki <rjw@rjwysocki.net>
    > ---
    > include/acpi/acpi_bus.h | 5 +++--
    > 1 file changed, 3 insertions(+), 2 deletions(-)
    >
    > diff --git a/include/acpi/acpi_bus.h b/include/acpi/acpi_bus.h
    > index d11eff8..0f131d2 100644
    > --- a/include/acpi/acpi_bus.h
    > +++ b/include/acpi/acpi_bus.h
    > @@ -407,7 +407,7 @@ static inline bool acpi_check_dma(struct acpi_device *adev, bool *coherent)
    > * case 1. Do not support and disable DMA.
    > * case 2. Support but rely on arch-specific cache maintenance for
    > * non-coherence DMA operations.
    > - * Currently, we implement case 1 above.
    > + * Currently, we implement case 2 above.
    > *
    > * For the case when _CCA is missing (i.e. cca_seen=0) and
    > * platform specifies ACPI_CCA_REQUIRED, we do not support DMA,
    > @@ -415,7 +415,8 @@ static inline bool acpi_check_dma(struct acpi_device *adev, bool *coherent)
    > *
    > * See acpi_init_coherency() for more info.
    > */
    > - if (adev->flags.coherent_dma) {
    > + if (adev->flags.coherent_dma ||
    > + (adev->flags.cca_seen && IS_ENABLED(CONFIG_ARM64))) {
    > ret = true;
    > if (coherent)
    > *coherent = adev->flags.coherent_dma;

    Hi Suravee,

    The acpi_check_dma function has been removed in patch 6 of this patch set, why it is still be used
    here, am I missing something? If the acpi_check_dma will be used in the future, personally I'd like
    to use IS_ENABLED(CONFIG_ACPI_CCA_REQUIRED) while not CONFIG_ARM64 macro here, or since _CCA attribute
    is arch-specific, it's reasonable to leave the _CCA handling policy to the arch-specific code. For example,
    with a link weak function like acpi_arch_check_dma() as a default handling if no arch-specific code
    provided, the actual _CCA handling will be implemented in the ARM, Intel or other Arch if required.

    Thanks,
    Dennis

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