Re: [PATCH V5 1/9] ACPI: Honor ACPI _CCA attribute setting

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Hi Dennis,

On 11/02/2015 12:02 PM, Dennis Chen wrote:
On Thu, Oct 29, 2015 at 6:50 AM, Suravee Suthikulpanit <Suravee.Suthikulpanit@xxxxxxx> wrote:
From: Jeremy Linton <jeremy.linton@xxxxxxx>

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@xxxxxxx>
Signed-off-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@xxxxxxx>
CC: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
CC: Catalin Marinas <catalin.marinas@xxxxxxx>
CC: Rob Herring <robh+dt@xxxxxxxxxx>
CC: Will Deacon <will.deacon@xxxxxxx>
CC: Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>
---
  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

I think this patch just to let people know that there is
case that arch-specific cache maintenance is still needed
for ACPI (such as Juno board), and in the later patches will
cover this case.

acpi_check_dma() will be replaced by acpi_get_dma_attr(),
and in acpi_get_dma_attr() will cover that case and will
be easily understood. (Suravee, correct me if I'm wrong :) )

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.

Actually Intel platform don't need _CCA and it's coherent
in default, since _CCA is in ACPI spec, I would like it's
handled in ACPI core.

Thanks
Hanjun
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