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From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Christoph Hellwig <hch@lst.de>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Robin Murphy <robin.murphy@arm.com>,
	Felipe Balbi <balbi@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"James E . J . Bottomley" <jejb@linux.vnet.ibm.com>,
	"Martin K . Petersen" <martin.petersen@oracle.com>,
	Andrew Morton <akpm@linux-foundation.org>
Cc: iommu@lists.linux-foundation.org, linux-usb@vger.kernel.org,
	linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org,
	Geert Uytterhoeven <geert@linux-m68k.org>
Subject: [PATCH v2 1/5] dma-mapping: Convert NO_DMA get_dma_ops() into a real dummy
Date: Fri, 16 Mar 2018 14:25:40 +0100	[thread overview]
Message-ID: <1521206744-1504-2-git-send-email-geert@linux-m68k.org> (raw)
In-Reply-To: <1521206744-1504-1-git-send-email-geert@linux-m68k.org>

If NO_DMA=y, get_dma_ops() returns a reference to the
non-existing symbol bad_dma_ops, thus causing a link failure if it is
ever used.

Make get_dma_ops() return NULL instead, to avoid the link failure.
This allows to improve compile-testing, and limits the need to keep on
sprinkling dependencies on HAS_DMA all over the place.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Acked-by: Robin Murphy <robin.murphy@arm.com>
---
v2:
  - Add Reviewed-by, Acked-by,
  - Drop RFC state.
---
 include/linux/dma-mapping.h | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index eb9eab4ecd6d7a05..5ea7eec83c0fbb82 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -212,14 +212,14 @@ static inline void set_dma_ops(struct device *dev,
 }
 #else
 /*
- * Define the dma api to allow compilation but not linking of
- * dma dependent code.  Code that depends on the dma-mapping
- * API needs to set 'depends on HAS_DMA' in its Kconfig
+ * Define the dma api to allow compilation of dma dependent code.
+ * Code that depends on the dma-mapping API needs to set 'depends on HAS_DMA'
+ * in its Kconfig, unless it already depends on <something> || COMPILE_TEST,
+ * where <something> guarantuees the availability of the dma-mapping API.
  */
-extern const struct dma_map_ops bad_dma_ops;
 static inline const struct dma_map_ops *get_dma_ops(struct device *dev)
 {
-	return &bad_dma_ops;
+	return NULL;
 }
 #endif
 
-- 
2.7.4

  reply	other threads:[~2018-03-16 13:25 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-03-16 13:25 [PATCH v2 0/5] Allow compile-testing NO_DMA (core) Geert Uytterhoeven
2018-03-16 13:25 ` Geert Uytterhoeven [this message]
2018-03-16 13:25 ` [PATCH v2 2/5] dma-coherent: Add NO_DMA dummies for managed DMA API Geert Uytterhoeven
2018-03-16 13:25 ` [PATCH v2 3/5] usb: gadget: Add NO_DMA dummies for DMA mapping API Geert Uytterhoeven
2018-03-16 14:34   ` Greg Kroah-Hartman
2018-03-16 13:25 ` [PATCH v2 4/5] mm: Add NO_DMA dummies for DMA pool API Geert Uytterhoeven
2018-03-16 13:25 ` [PATCH v2 5/5] scsi: Add NO_DMA dummies for SCSI DMA mapping API Geert Uytterhoeven
2018-03-16 18:59 ` [PATCH v2 0/5] Allow compile-testing NO_DMA (core) Christoph Hellwig

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