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Date:	Fri, 08 May 2015 22:53:59 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
Cc:	lenb@...nel.org, catalin.marinas@....com, will.deacon@....com,
	thomas.lendacky@....com, herbert@...dor.apana.org.au,
	davem@...emloft.net, arnd@...db.de, msalter@...hat.com,
	hanjun.guo@...aro.org, al.stone@...aro.org,
	grant.likely@...aro.org, leo.duran@....com,
	linux-arm-kernel@...ts.infradead.org, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org, linaro-acpi@...ts.linaro.org,
	netdev@...r.kernel.org, linux-crypto@...r.kernel.org
Subject: Re: [V3 PATCH 1/5] ACPI / scan: Parse _CCA and setup device coherency

On Thursday, May 07, 2015 07:37:12 PM 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@...hat.com>
> Signed-off-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
> ---
>  drivers/acpi/Kconfig         |  6 ++++++
>  drivers/acpi/acpi_platform.c | 10 +++++++---
>  drivers/acpi/scan.c          | 42 ++++++++++++++++++++++++++++++++++++++++++
>  include/acpi/acpi_bus.h      | 32 +++++++++++++++++++++++++++++++-
>  include/linux/acpi.h         | 10 ++++++++++
>  5 files changed, 96 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
> index ab2cbb5..7822149 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_CCA_REQUIRED
> +	bool
> +
> +config ARM64_SUPPORT_ACPI_CCA_ZERO

Hmm.  I guess the Arnd's idea what to simply use CONFIG_ARM64 directly instead
of adding this new option.

> +	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..a084ea0 100644
> --- a/drivers/acpi/acpi_platform.c
> +++ b/drivers/acpi/acpi_platform.c
> @@ -103,14 +103,18 @@ struct platform_device *acpi_create_platform_device(struct acpi_device *adev)
>  	pdevinfo.res = resources;
>  	pdevinfo.num_res = count;
>  	pdevinfo.fwnode = acpi_fwnode_handle(adev);
> -	pdevinfo.dma_mask = DMA_BIT_MASK(32);
> +	pdevinfo.dma_mask = acpi_dma_is_supported(adev)? DMA_BIT_MASK(32): 0;

Spaces before the "?" and ":", please.

>  	pdev = platform_device_register_full(&pdevinfo);
> -	if (IS_ERR(pdev))
> +	if (IS_ERR(pdev)) {
>  		dev_err(&adev->dev, "platform device creation failed: %ld\n",
>  			PTR_ERR(pdev));
> -	else
> +	} else {
> +		if (acpi_dma_is_supported(adev))
> +			arch_setup_dma_ops(&pdev->dev, 0, 0, NULL,
> +					   acpi_dma_is_coherent(adev));

OK, so I understand why this is needed, but ->

>  		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..0976dc2 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 +2138,46 @@ void acpi_free_pnp_ids(struct acpi_device_pnp *pnp)
>  	kfree(pnp->unique_id);
>  }
>  
> +static void acpi_init_coherency(struct acpi_device *adev)
> +{
> +	unsigned long long cca = 0;
> +	acpi_status status;
> +	struct acpi_device *parent = adev->parent;
> +	struct acpi_buffer buffer = { ACPI_ALLOCATE_BUFFER, NULL };
> +
> +	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_CCA_REQUIRED)) {
> +			/*
> +			 * If architecture does not specify that _CCA is
> +			 * required for DMA-able devices (e.g. x86),
> +			 * we default to _CCA=1.
> +			 */
> +			cca = 1;
> +		} else {
> +			acpi_get_name(adev->handle, ACPI_FULL_PATHNAME, &buffer);
> +			pr_debug("ACPI device %s is missing _CCA.\n",
> +				(char *) buffer.pointer);
> +			kfree(buffer.pointer);
> +		}
> +	}
> +
> +	adev->flags.is_coherent = cca;
> +	if (acpi_dma_is_supported(adev))
> +		arch_setup_dma_ops(&adev->dev, 0, 0, NULL,
> +				   acpi_dma_is_coherent(adev));

Why do we need this one?  adev->dev is not a device, it is an ACPI namespace
node representation.  Why do you want to set up DMA ops for it?

Would you set up DMA ops for a struct device_node?

> +}
> +
>  void acpi_init_device_object(struct acpi_device *device, acpi_handle handle,
>  			     int type, unsigned long long sta)
>  {
> @@ -2155,6 +2196,7 @@ 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..17fb630 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;
>  };
>  
>  /* File System */
> @@ -380,6 +382,34 @@ struct acpi_device {
>  	void (*remove)(struct acpi_device *);
>  };
>  
> +static inline bool acpi_dma_is_supported(struct acpi_device *adev)
> +{
> +	/**
> +	 * Currently, we mainly support _CCA=1 (i.e. is_coherent=1)
> +	 * This should be equivalent to specifyig dma-coherent for
> +	 * a device in OF.
> +	 *
> +	 * 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 specifies
> +	 * _XXX_SUPPORT_CCA_ZERO. Otherwise, we do not support
> +	 * DMA on this device and fallback to arch-specific default
> +	 * handling.
> +	 *
> +	 * For the case when _CCA is missing (i.e. cca_seen=0) but
> +	 * platform specifies ACPI_CCA_REQUIRED, we do not support DMA,
> +	 * and fallback to arch-specific default handling.
> +	 */
> +	return adev && (adev->flags.is_coherent ||
> +			(adev->flags.cca_seen &&
> +			 IS_ENABLED(CONFIG_ARM64_SUPPORT_ACPI_CCA_ZERO)));

So what exactly would be wrong with using IS_ENABLED(CONFIG_ARM64) here?

> +}
> +
> +static inline bool acpi_dma_is_coherent(struct acpi_device *adev)
> +{
> +	return adev && adev->flags.is_coherent;
> +}
> +
>  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..baccf3b 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -583,6 +583,16 @@ static inline int acpi_device_modalias(struct device *dev,
>  	return -ENODEV;
>  }
>  
> +static inline bool acpi_dma_is_supported(struct acpi_device *adev)
> +{
> +	return false;
> +}
> +
> +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.
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