From: Russell King <rmk+kernel@arm.linux.org.uk> To: linux-arm-kernel@lists.infradead.org, linux-omap@vger.kernel.org, linux-mmc@vger.kernel.org Cc: Tony Lindgren <tony@atomide.com> Subject: [PATCH 1/8] ARM: OMAP: fix DMA vs memory ordering Date: Wed, 18 Apr 2012 11:10:35 +0100 [thread overview] Message-ID: <E1SKRqN-0004b4-Me@rmk-PC.arm.linux.org.uk> (raw) In-Reply-To: <20120418100954.GK25053@n2100.arm.linux.org.uk> Using coherent DMA memory with the OMAP DMA engine results in unpredictable behaviour due to memory ordering issues; as things stand, there is no guarantee that data written to coherent DMA memory will be visible to the DMA hardware. This is because the OMAP dma_write() accessor contains no barriers, necessary on ARMv6 and above. The effect of this can be seen in comments in the OMAP serial driver, which incorrectly talks about cache flushing for the coherent DMA stuff. Rather than adding barriers to the accessors, add it in the DMA support code just before we enable DMA, and just after we disable DMA. This avoids having barriers for every DMA register access. Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk> --- arch/arm/plat-omap/dma.c | 14 ++++++++++++++ 1 files changed, 14 insertions(+), 0 deletions(-) diff --git a/arch/arm/plat-omap/dma.c b/arch/arm/plat-omap/dma.c index ecdb3da..c58d896 100644 --- a/arch/arm/plat-omap/dma.c +++ b/arch/arm/plat-omap/dma.c @@ -916,6 +916,13 @@ void omap_start_dma(int lch) l |= OMAP_DMA_CCR_BUFFERING_DISABLE; l |= OMAP_DMA_CCR_EN; + /* + * As dma_write() uses IO accessors which are weakly ordered, there + * is no guarantee that data in coherent DMA memory will be visible + * to the DMA device. Add a memory barrier here to ensure that any + * such data is visible prior to enabling DMA. + */ + mb(); p->dma_write(l, CCR, lch); dma_chan[lch].flags |= OMAP_DMA_ACTIVE; @@ -965,6 +972,13 @@ void omap_stop_dma(int lch) p->dma_write(l, CCR, lch); } + /* + * Ensure that data transferred by DMA is visible to any access + * after DMA has been disabled. This is important for coherent + * DMA regions. + */ + mb(); + if (!omap_dma_in_1510_mode() && dma_chan[lch].next_lch != -1) { int next_lch, cur_lch = lch; char dma_chan_link_map[dma_lch_count]; -- 1.7.4.4
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From: rmk+kernel@arm.linux.org.uk (Russell King) To: linux-arm-kernel@lists.infradead.org Subject: [PATCH 1/8] ARM: OMAP: fix DMA vs memory ordering Date: Wed, 18 Apr 2012 11:10:35 +0100 [thread overview] Message-ID: <E1SKRqN-0004b4-Me@rmk-PC.arm.linux.org.uk> (raw) In-Reply-To: <20120418100954.GK25053@n2100.arm.linux.org.uk> Using coherent DMA memory with the OMAP DMA engine results in unpredictable behaviour due to memory ordering issues; as things stand, there is no guarantee that data written to coherent DMA memory will be visible to the DMA hardware. This is because the OMAP dma_write() accessor contains no barriers, necessary on ARMv6 and above. The effect of this can be seen in comments in the OMAP serial driver, which incorrectly talks about cache flushing for the coherent DMA stuff. Rather than adding barriers to the accessors, add it in the DMA support code just before we enable DMA, and just after we disable DMA. This avoids having barriers for every DMA register access. Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk> --- arch/arm/plat-omap/dma.c | 14 ++++++++++++++ 1 files changed, 14 insertions(+), 0 deletions(-) diff --git a/arch/arm/plat-omap/dma.c b/arch/arm/plat-omap/dma.c index ecdb3da..c58d896 100644 --- a/arch/arm/plat-omap/dma.c +++ b/arch/arm/plat-omap/dma.c @@ -916,6 +916,13 @@ void omap_start_dma(int lch) l |= OMAP_DMA_CCR_BUFFERING_DISABLE; l |= OMAP_DMA_CCR_EN; + /* + * As dma_write() uses IO accessors which are weakly ordered, there + * is no guarantee that data in coherent DMA memory will be visible + * to the DMA device. Add a memory barrier here to ensure that any + * such data is visible prior to enabling DMA. + */ + mb(); p->dma_write(l, CCR, lch); dma_chan[lch].flags |= OMAP_DMA_ACTIVE; @@ -965,6 +972,13 @@ void omap_stop_dma(int lch) p->dma_write(l, CCR, lch); } + /* + * Ensure that data transferred by DMA is visible to any access + * after DMA has been disabled. This is important for coherent + * DMA regions. + */ + mb(); + if (!omap_dma_in_1510_mode() && dma_chan[lch].next_lch != -1) { int next_lch, cur_lch = lch; char dma_chan_link_map[dma_lch_count]; -- 1.7.4.4
next prev parent reply other threads:[~2012-04-18 10:10 UTC|newest] Thread overview: 120+ messages / expand[flat|nested] mbox.gz Atom feed top 2012-04-18 10:09 [RFC 0/8] DMA engine conversion for omap_hsmmc Russell King - ARM Linux 2012-04-18 10:09 ` Russell King - ARM Linux 2012-04-18 10:10 ` Russell King [this message] 2012-04-18 10:10 ` [PATCH 1/8] ARM: OMAP: fix DMA vs memory ordering Russell King 2012-04-18 10:15 ` Felipe Balbi 2012-04-18 10:15 ` Felipe Balbi 2012-04-18 10:17 ` Russell King - ARM Linux 2012-04-18 10:17 ` Russell King - ARM Linux 2012-04-18 10:18 ` Felipe Balbi 2012-04-18 10:18 ` Felipe Balbi 2012-04-18 10:26 ` Russell King - ARM Linux 2012-04-18 10:26 ` Russell King - ARM Linux 2012-04-20 22:22 ` Tony Lindgren 2012-04-20 22:22 ` Tony Lindgren 2012-04-23 14:19 ` Russell King - ARM Linux 2012-04-23 14:19 ` Russell King - ARM Linux 2012-04-23 14:27 ` Tony Lindgren 2012-04-23 14:27 ` Tony Lindgren 2012-04-23 14:35 ` Shilimkar, Santosh 2012-04-23 14:35 ` Shilimkar, Santosh 2012-04-18 10:10 ` [PATCH 2/8] dmaengine: amba-pl08x: ensure physical channels are properly held Russell King 2012-04-18 10:10 ` Russell King 2012-04-18 10:19 ` Russell King - ARM Linux 2012-04-18 10:19 ` Russell King - ARM Linux 2012-04-27 20:38 ` Linus Walleij 2012-04-27 20:38 ` Linus Walleij 2012-04-27 21:41 ` Russell King - ARM Linux 2012-04-27 21:41 ` Russell King - ARM Linux 2012-04-18 10:11 ` [PATCH 3/8] dmaengine: split out virtual channel DMA support from sa11x0 driver Russell King 2012-04-18 10:11 ` Russell King 2012-04-24 10:35 ` Laxman Dewangan 2012-04-24 10:35 ` Laxman Dewangan 2012-04-24 10:50 ` Russell King - ARM Linux 2012-04-24 10:50 ` Russell King - ARM Linux 2012-04-24 10:57 ` Laxman Dewangan 2012-04-24 10:57 ` Laxman Dewangan 2012-04-18 10:11 ` [PATCH 4/8] dmaengine: add OMAP DMA engine driver Russell King 2012-04-18 10:11 ` Russell King 2012-04-18 10:11 ` [PATCH 5/8] mmc: omap_hsmmc: release correct resource Russell King 2012-04-18 10:11 ` Russell King 2012-04-20 22:23 ` Tony Lindgren 2012-04-20 22:23 ` Tony Lindgren 2012-04-20 22:59 ` Chris Ball 2012-04-20 22:59 ` Chris Ball 2012-04-21 2:35 ` Chris Ball 2012-04-21 2:35 ` Chris Ball 2012-04-21 9:48 ` Russell King - ARM Linux 2012-04-21 9:48 ` Russell King - ARM Linux 2012-04-22 15:20 ` Chris Ball 2012-04-22 15:20 ` Chris Ball 2012-04-18 10:12 ` [PATCH 6/8] mmc: omap_hsmmc: add DMA engine support Russell King 2012-04-18 10:12 ` Russell King 2012-04-18 18:11 ` Tony Lindgren 2012-04-18 18:11 ` Tony Lindgren 2012-04-18 19:09 ` Russell King - ARM Linux 2012-04-18 19:09 ` Russell King - ARM Linux 2012-04-18 19:53 ` Tony Lindgren 2012-04-18 19:53 ` Tony Lindgren 2012-04-18 10:12 ` [PATCH 7/8] mmc: omap_hsmmc: remove private DMA API implementation Russell King 2012-04-18 10:12 ` Russell King 2012-04-18 10:12 ` [PATCH 8/8] ARM: omap_hsmmc: remove platform data dma_mask and initialization Russell King 2012-04-18 10:12 ` Russell King 2012-04-18 15:23 ` T Krishnamoorthy, Balaji 2012-04-18 15:23 ` T Krishnamoorthy, Balaji 2012-04-18 15:29 ` Russell King - ARM Linux 2012-04-18 15:29 ` Russell King - ARM Linux 2012-04-18 15:35 ` T Krishnamoorthy, Balaji 2012-04-18 15:35 ` T Krishnamoorthy, Balaji 2012-04-18 18:19 ` Tony Lindgren 2012-04-18 18:19 ` Tony Lindgren 2012-04-18 19:10 ` Russell King - ARM Linux 2012-04-18 19:10 ` Russell King - ARM Linux 2012-04-18 19:55 ` Tony Lindgren 2012-04-18 19:55 ` Tony Lindgren 2012-04-18 19:42 ` Russell King - ARM Linux 2012-04-18 19:42 ` Russell King - ARM Linux 2012-04-18 20:02 ` Tony Lindgren 2012-04-18 20:02 ` Tony Lindgren 2012-04-18 20:24 ` Russell King - ARM Linux 2012-04-18 20:24 ` Russell King - ARM Linux 2012-04-18 21:01 ` Tony Lindgren 2012-04-18 21:01 ` Tony Lindgren 2012-04-18 21:16 ` Russell King - ARM Linux 2012-04-18 21:16 ` Russell King - ARM Linux 2012-04-18 21:34 ` Tony Lindgren 2012-04-18 21:34 ` Tony Lindgren 2012-04-18 21:36 ` Russell King - ARM Linux 2012-04-18 21:36 ` Russell King - ARM Linux 2012-04-19 1:39 ` Tony Lindgren 2012-04-19 1:39 ` Tony Lindgren 2012-04-19 17:43 ` Russell King - ARM Linux 2012-04-19 17:43 ` Russell King - ARM Linux 2012-04-19 18:07 ` Tony Lindgren 2012-04-19 18:07 ` Tony Lindgren 2012-04-20 15:10 ` Russell King - ARM Linux 2012-04-20 15:10 ` Russell King - ARM Linux 2012-04-20 15:26 ` Tony Lindgren 2012-04-20 15:26 ` Tony Lindgren 2012-04-20 15:37 ` Russell King - ARM Linux 2012-04-20 15:37 ` Russell King - ARM Linux 2012-04-20 16:43 ` Tony Lindgren 2012-04-20 16:43 ` Tony Lindgren 2012-04-20 22:09 ` Russell King - ARM Linux 2012-04-20 22:09 ` Russell King - ARM Linux 2012-04-20 22:21 ` Tony Lindgren 2012-04-20 22:21 ` Tony Lindgren 2012-04-20 16:50 ` Tony Lindgren 2012-04-20 16:50 ` Tony Lindgren 2012-04-23 14:14 ` Russell King - ARM Linux 2012-04-23 14:14 ` Russell King - ARM Linux 2012-04-23 14:30 ` Tony Lindgren 2012-04-23 14:30 ` Tony Lindgren 2012-04-23 14:34 ` Russell King - ARM Linux 2012-04-23 14:34 ` Russell King - ARM Linux 2012-04-23 11:46 ` [RFC 0/8] DMA engine conversion Russell King - ARM Linux 2012-04-23 11:46 ` Russell King - ARM Linux 2012-04-23 12:32 ` Shilimkar, Santosh 2012-04-23 12:32 ` Shilimkar, Santosh 2012-04-23 15:27 ` Shubhrajyoti 2012-04-23 15:27 ` Shubhrajyoti
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