linux-kernel - Re: [V3 PATCH 3/5] device property: Introduces device_dma_is

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Message-ID: <554D1E36.1030607@oracle.com>
Date:	Fri, 08 May 2015 13:36:06 -0700
From:	santosh shilimkar <santosh.shilimkar@...cle.com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
CC:	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
	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 3/5] device property: Introduces device_dma_is_coherent()

On 5/8/2015 1:58 PM, Rafael J. Wysocki wrote:
> On Friday, May 08, 2015 01:27:00 PM santosh shilimkar wrote:
>> On 5/8/2015 1:49 PM, Rafael J. Wysocki wrote:
>>> On Thursday, May 07, 2015 09:12:00 PM santosh.shilimkar@...cle.com wrote:
>>>> On 5/7/15 5:37 PM, Suravee Suthikulpanit wrote:
>>>>> Currently, device drivers, which support both OF and ACPI,
>>>>> need to call two separate APIs, of_dma_is_coherent() and
>>>>> acpi_dma_is_coherent()) to determine device coherency attribute.
>>>>>
>>>>> This patch simplifies this process by introducing a new device
>>>>> property API, device_dma_is_coherent(), which calls the appropriate
>>>>> interface based on the booting architecture.
>>>>>
>>>>> Signed-off-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
>>>>> ---
>>>>>     drivers/base/property.c  | 12 ++++++++++++
>>>>>     include/linux/property.h |  2 ++
>>>>>     2 files changed, 14 insertions(+)
>>>>>
>>>>> diff --git a/drivers/base/property.c b/drivers/base/property.c
>>>>> index 1d0b116..8123c6e 100644
>>>>> --- a/drivers/base/property.c
>>>>> +++ b/drivers/base/property.c
>>>>> @@ -14,6 +14,7 @@
>>>>>     #include <linux/export.h>
>>>>>     #include <linux/kernel.h>
>>>>>     #include <linux/of.h>
>>>>> +#include <linux/of_address.h>
>>>>>     #include <linux/property.h>
>>>>>
>>>>>     /**
>>>>> @@ -519,3 +520,14 @@ unsigned int device_get_child_node_count(struct device *dev)
>>>>>     	return count;
>>>>>     }
>>>>>     EXPORT_SYMBOL_GPL(device_get_child_node_count);
>>>>> +
>>>>> +bool device_dma_is_coherent(struct device *dev)
>>>>> +{
>>>>> +	if (IS_ENABLED(CONFIG_OF) && dev->of_node)
>>>>
>>>> Do you really need that IS_ENABLED(CONFIG_OF) ?
>>>> In other words, dev->of_node should be null for !CONFIG_OF
>>>
>>> Yes, but IS_ENABLED(CONFIG_OF) causes the check to be optimized away by the
>>> compiler if CONFIG_OF is not enabled.
>>>
>> Sure but my point was why you need it when just 'dev->of_node' check
>> is enough. May be I missed something.
>
> dev->of_node is present when CONFIG_OF is not enabled too.  Without the
> IS_ENABLED(CONFIG_OF) this becomes a pointless pointer check that will
> always evaluate to 'false' on systems without CONFIG_OF, AFAICS.
>
Got it now. Thanks for expanding it.

Regards,
Santosh
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