linux-kernel - Re: [PATCH 2/2] dw_dmac: max_mem_width limits value for SRC/DST_TR

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Date:	Mon, 27 Aug 2012 15:48:38 +0800
From:	Hein Tibosch <hein_tibosch@...oo.es>
To:	Viresh Kumar <viresh.kumar@...aro.org>
CC:	spear-devel <spear-devel@...t.st.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"ludovic.desroches" <ludovic.desroches@...el.com>,
	Havard Skinnemoen <havard@...nnemoen.net>,
	Nicolas Ferre <nicolas.ferre@...el.com>, egtvedt@...fundet.no,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arnd Bergmann <arnd.bergmann@...aro.org>, vinod.koul@...el.com,
	dan.j.williams@...el.com
Subject: Re: [PATCH 2/2] dw_dmac: max_mem_width limits value for SRC/DST_TR_WID
 register

On 8/27/2012 11:47 AM, Viresh Kumar wrote:
> On 27 August 2012 02:11, Hein Tibosch <hein_tibosch@...oo.es <mailto:hein_tibosch@...oo.es>> wrote:
>
>     The dw_dmac driver was earlier adapted to do 64-bit transfers
>     on the memory side (https://lkml.org/lkml/2012/1/18/52)
>     This works on ARM platforms but for AVR32 (AP700x) the maximum
>     allowed transfer size is 32-bits.
>     This patch allows the arch to set a new slave property
>     max_mem_width to limit the size.
>     Allowable values for dw_dma_slave::max_mem_width are:
>
>     0 : leave it up to dw_dmac (64 bits)
>     1 : 16-bits
>     2 : 32-bits
>
>
> Either this should be in increasing order or decreasing. That will make it
> more sensible, isn't it?
>
> So it should be:
> 0-64bit
> 1-32bit
> 2-16bit
>
> Also, i am not sure if we should actually support 16 bit here at all. Maybe nobody
> will have 16 bit requirement. So can remove it for now. If in future it is required
> then can accept that.
>  
Viresh,

If you're OK with the version below, I'll send both dw_dmac patches
again as v2

Now cc Vinod Koul and Dan Williams

The dw_dmac driver was earlier adapted to do 64-bit transfers
on the memory side (https://lkml.org/lkml/2012/1/18/52)
This works on ARM platforms but for AVR32 (AP700x) the maximum
allowed transfer size is 32-bits.

A new 'automatic' config item 'DW_DMAC_MEM_64_BIT' determines if 64-bit
memory transfers are allowed. This boolean will be defined on non-AVR32
platforms

No arch code will have to be changed to make this patch work.

Signed-off-by: Hein Tibosch <hein_tibosch@...oo.es>
---
 drivers/dma/Kconfig   |    8 ++++++++
 drivers/dma/dw_dmac.c |   15 ++++++++++++---
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/drivers/dma/Kconfig b/drivers/dma/Kconfig
index 3635daf..82e958f 100644
--- a/drivers/dma/Kconfig
+++ b/drivers/dma/Kconfig
@@ -97,6 +97,14 @@ config DW_DMAC_BE
 	  Say yes if access to the Synopsys DesignWare AHB DMA controller
 	  should be big endian, such as for Atmel AT32ap7000
 
+config DW_DMAC_MEM_64_BIT
+	bool "Allow Synopsys DesignWare AHB DMA to do 64-bit mem transfers"
+	default y if !AVR32
+	depends on DW_DMAC
+	help
+	  Say yes if the Synopsys DesignWare AHB DMA controller may do
+	  64-bit memory transfers
+
 config AT_HDMAC
 	tristate "Atmel AHB DMA support"
 	depends on ARCH_AT91
diff --git a/drivers/dma/dw_dmac.c b/drivers/dma/dw_dmac.c
index 7212961..2be010c 100644
--- a/drivers/dma/dw_dmac.c
+++ b/drivers/dma/dw_dmac.c
@@ -639,9 +639,12 @@ dwc_prep_dma_memcpy(struct dma_chan *chan, dma_addr_t dest, dma_addr_t src,
 	 * We can be a lot more clever here, but this should take care
 	 * of the most common optimization.
 	 */
+#ifdef	DW_DMAC_MEM_64_BIT
 	if (!((src | dest  | len) & 7))
 		src_width = dst_width = 3;
-	else if (!((src | dest  | len) & 3))
+	else
+#endif
+	if (!((src | dest  | len) & 3))
 		src_width = dst_width = 2;
 	else if (!((src | dest | len) & 1))
 		src_width = dst_width = 1;
@@ -746,9 +749,12 @@ dwc_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
 			mem = sg_dma_address(sg);
 			len = sg_dma_len(sg);
 
+#ifdef	DW_DMAC_MEM_64_BIT
 			if (!((mem | len) & 7))
 				mem_width = 3;
-			else if (!((mem | len) & 3))
+			else
+#endif
+			if (!((mem | len) & 3))
 				mem_width = 2;
 			else if (!((mem | len) & 1))
 				mem_width = 1;
@@ -813,9 +819,12 @@ slave_sg_todev_fill_desc:
 			mem = sg_dma_address(sg);
 			len = sg_dma_len(sg);
 
+#ifdef	DW_DMAC_MEM_64_BIT
 			if (!((mem | len) & 7))
 				mem_width = 3;
-			else if (!((mem | len) & 3))
+			else
+#endif
+			if (!((mem | len) & 3))
 				mem_width = 2;
 			else if (!((mem | len) & 1))
 				mem_width = 1;
-- 
1.7.8.0

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