Re: [V2 PATCH 1/5] ACPI / scan: Parse _CCA and setup device coherency

Rafael J. Wysocki
2015-05-05T20:11:55Z

On Tuesday, May 05, 2015 10:12:05 AM Suravee Suthikulpanit wrote:
> This patch implements support for ACPI _CCA object, which is introduced in
> ACPIv5.1, can be used for specifying device DMA coherency attribute.
>
> The parsing logic traverses device namespace to parse coherency
> information, and stores it in acpi_device_flags. Then uses it to call
> arch_setup_dma_ops() when creating each device enumerated in DSDT
> during ACPI scan.
>
> This patch also introduces acpi_dma_is_coherent(), which provides
> an interface for device drivers to check the coherency information
> similarly to the of_dma_is_coherent().
>
> Signed-off-by: Mark Salter <msalter@redhat.com>
> Signed-off-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>
> ---
> NOTE:
> * Since there seem to be conflict opinions regarding how
> architecture should handle _CCA=0. So, I am proposing the
> CONFIG_ARCH_SUPPORT_CCA_ZERO, which can be specified by
> for each architecture to define behavior of the ACPI
> scanning code when _CCA=0. Let me know if this is acceptable.
>
> drivers/acpi/Kconfig | 6 +++++
> drivers/acpi/acpi_platform.c | 4 ++-
> drivers/acpi/scan.c | 62 ++++++++++++++++++++++++++++++++++++++++++++
> include/acpi/acpi_bus.h | 11 +++++++-
> include/linux/acpi.h | 5 ++++
> 5 files changed, 86 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
> index ab2cbb5..dd386e9 100644
> --- a/drivers/acpi/Kconfig
> +++ b/drivers/acpi/Kconfig
> @@ -54,6 +54,12 @@ config ACPI_GENERIC_GSI
> config ACPI_SYSTEM_POWER_STATES_SUPPORT
> bool
>
> +config ACPI_MUST_HAVE_CCA

ACPI_CCA_REQUIRED maybe?

> + bool
> +
> +config ACPI_SUPPORT_CCA_ZERO

I guess this means "we support devices that can DMA, but are not coherent".
right?

> + bool
> +
> config ACPI_SLEEP
> bool
> depends on SUSPEND || HIBERNATION
> diff --git a/drivers/acpi/acpi_platform.c b/drivers/acpi/acpi_platform.c
> index 4bf7559..a6feca4 100644
> --- a/drivers/acpi/acpi_platform.c
> +++ b/drivers/acpi/acpi_platform.c
> @@ -108,9 +108,11 @@ struct platform_device *acpi_create_platform_device(struct acpi_device *adev)
> if (IS_ERR(pdev))
> dev_err(&adev->dev, "platform device creation failed: %ld\n",
> PTR_ERR(pdev));
> - else
> + else {

Please add braces to both branches when making such changes (as per CodingStyle).

> + acpi_setup_device_dma(adev, &pdev->dev);

Why do we need to do that here (for the second time)?

> dev_dbg(&adev->dev, "created platform device %s\n",
> dev_name(&pdev->dev));
> + }
>
> kfree(resources);
> return pdev;
> diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
> index 849b699..ac33b29 100644
> --- a/drivers/acpi/scan.c
> +++ b/drivers/acpi/scan.c
> @@ -11,6 +11,7 @@
> #include <linux/kthread.h>
> #include <linux/dmi.h>
> #include <linux/nls.h>
> +#include <linux/dma-mapping.h>
>
> #include <asm/pgtable.h>
>
> @@ -2137,6 +2138,66 @@ void acpi_free_pnp_ids(struct acpi_device_pnp *pnp)
> kfree(pnp->unique_id);
> }
>
> +void acpi_setup_device_dma(struct acpi_device *adev, struct device *dev)
> +{
> + int coherent = acpi_dma_is_coherent(adev);
> +
> + /**
> + * Currently, we only support DMA for devices that _CCA=1
> + * since this seems to be the case on most ACPI platforms.
> + *
> + * For the case when _CCA=0 (i.e. is_coherent=0 && cca_seen=1),
> + * we would rely on arch-specific cache maintenance for
> + * non-coherence DMA operations if architecture enables
> + * CONFIG_ACPI_SUPPORT_CCA_ZERO.
> + *
> + * For the case when _CCA is missing but platform requires it
> + * (i.e. is_coherent=0 && cca_seen=0), we do not call
> + * arch_setup_dma_ops() and fallback to arch-specific default
> + * handling.
> + */
> + if (adev->flags.cca_seen) {
> + if (!coherent && !IS_ENABLED(CONFIG_ACPI_SUPPORT_CCA_ZERO))
> + return;
> + arch_setup_dma_ops(dev, 0, 0, NULL, coherent);

Oh dear.

What about

if (adev->flags.cca_seen && (coherent || IS_ENABLED(CONFIG_ACPI_SUPPORT_CCA_ZERO)))
arch_setup_dma_ops(dev, 0, 0, NULL, coherent);

I wonder how this is going to affect x86/ia64 too?

> + }
> +}
> +
> +static void acpi_init_coherency(struct acpi_device *adev)
> +{
> + unsigned long long cca = 0;
> + acpi_status status;
> + struct acpi_device *parent = adev->parent;
> +
> + if (parent && parent->flags.cca_seen) {
> + /*
> + * From ACPI spec, OSPM will ignore _CCA if an ancestor
> + * already saw one.
> + */
> + adev->flags.cca_seen = 1;
> + cca = acpi_dma_is_coherent(parent);
> + } else {
> + status = acpi_evaluate_integer(adev->handle, "_CCA",
> + NULL, &cca);
> + if (ACPI_SUCCESS(status)) {
> + adev->flags.cca_seen = 1;
> + } else if (!IS_ENABLED(CONFIG_ACPI_MUST_HAVE_CCA)) {
> + /*
> + * If architecture does not specify that _CCA is
> + * required for DMA-able devices (e.g. x86),
> + * we default to _CCA=1.
> + */
> + cca = 1;
> + } else {
> + dev_err(&adev->dev, FW_BUG
> + "DMA is not setup due to missing _CCA.\n");
> + }
> + }
> +
> + adev->flags.is_coherent = cca;
> + acpi_setup_device_dma(adev, &adev->dev);
> +}
> +
> void acpi_init_device_object(struct acpi_device *device, acpi_handle handle,
> int type, unsigned long long sta)
> {
> @@ -2155,6 +2216,7 @@ void acpi_init_device_object(struct acpi_device *device, acpi_handle handle,
> device->flags.visited = false;
> device_initialize(&device->dev);
> dev_set_uevent_suppress(&device->dev, true);
> + acpi_init_coherency(device);
> }
>
> void acpi_device_add_finalize(struct acpi_device *device)
> diff --git a/include/acpi/acpi_bus.h b/include/acpi/acpi_bus.h
> index 8de4fa9..b804183 100644
> --- a/include/acpi/acpi_bus.h
> +++ b/include/acpi/acpi_bus.h
> @@ -208,7 +208,9 @@ struct acpi_device_flags {
> u32 visited:1;
> u32 hotplug_notify:1;
> u32 is_dock_station:1;
> - u32 reserved:23;
> + u32 is_coherent:1;
> + u32 cca_seen:1;
> + u32 reserved:21;

That will conflict with a patch I've already queued up, but never mind.

> };
>
> /* File System */
> @@ -380,6 +382,13 @@ struct acpi_device {
> void (*remove)(struct acpi_device *);
> };
>
> +static inline bool acpi_dma_is_coherent(struct acpi_device *adev)
> +{
> + return adev && adev->flags.is_coherent;
> +}
> +
> +void acpi_setup_device_dma(struct acpi_device *adev, struct device *dev);
> +
> static inline bool is_acpi_node(struct fwnode_handle *fwnode)
> {
> return fwnode && fwnode->type == FWNODE_ACPI;
> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index b10c4a6..d14e777 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -583,6 +583,11 @@ static inline int acpi_device_modalias(struct device *dev,
> return -ENODEV;
> }
>
> +static inline bool acpi_dma_is_coherent(struct acpi_device *adev)
> +{
> + return false;
> +}
> +
> #define ACPI_PTR(_ptr) (NULL)
>
> #endif /* !CONFIG_ACPI */
>

--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.