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

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Message-ID: <6693356.eSISHsdLqF@vostro.rjw.lan>
Date:	Fri, 08 May 2015 22:58:43 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	santosh shilimkar <santosh.shilimkar@...cle.com>
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 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.


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