diff mbox

[RFC,v5,1/7] dma: Take into account dma_pfn_offset

Message ID 1484738003-29892-2-git-send-email-vladimir.murzin@arm.com
State New, archived
Headers show

Commit Message

Vladimir Murzin Jan. 18, 2017, 11:13 a.m. UTC
Even though dma-noop-ops assumes 1:1 memory mapping DMA memory range
can be different to RAM. For example, ARM STM32F4 MCU offers the
possibility to remap SDRAM from 0xc000_0000 to 0x0 to get CPU
performance boost, but DMA continue to see SDRAM at 0xc000_0000. This
difference in mapping is handled via device-tree "dma-range" property
which leads to dev->dma_pfn_offset is set nonzero. To handle such
cases take dma_pfn_offset into account.

Cc: Joerg Roedel <jroedel@suse.de>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Reported-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
---
 lib/dma-noop.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

Comments

Joerg Roedel Jan. 18, 2017, 1:47 p.m. UTC | #1
On Wed, Jan 18, 2017 at 11:13:17AM +0000, Vladimir Murzin wrote:
> Even though dma-noop-ops assumes 1:1 memory mapping DMA memory range
> can be different to RAM. For example, ARM STM32F4 MCU offers the
> possibility to remap SDRAM from 0xc000_0000 to 0x0 to get CPU
> performance boost, but DMA continue to see SDRAM at 0xc000_0000. This
> difference in mapping is handled via device-tree "dma-range" property
> which leads to dev->dma_pfn_offset is set nonzero. To handle such
> cases take dma_pfn_offset into account.
> 
> Cc: Joerg Roedel <jroedel@suse.de>
> Cc: Christian Borntraeger <borntraeger@de.ibm.com>
> Reported-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
> Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
> ---
>  lib/dma-noop.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/lib/dma-noop.c b/lib/dma-noop.c
> index 3d766e7..a14eee5 100644
> --- a/lib/dma-noop.c
> +++ b/lib/dma-noop.c
> @@ -7,6 +7,7 @@
>  #include <linux/mm.h>
>  #include <linux/dma-mapping.h>
>  #include <linux/scatterlist.h>
> +#include <linux/pfn.h>
>  
>  static void *dma_noop_alloc(struct device *dev, size_t size,
>  			    dma_addr_t *dma_handle, gfp_t gfp,
> @@ -16,7 +17,8 @@ static void *dma_noop_alloc(struct device *dev, size_t size,
>  
>  	ret = (void *)__get_free_pages(gfp, get_order(size));
>  	if (ret)
> -		*dma_handle = virt_to_phys(ret);
> +		*dma_handle = virt_to_phys(ret) - PFN_PHYS(dev->dma_pfn_offset);
> +

If you need to do a '-' operation here, the offset is basically a
cpu_pfn_offset for the device. Is that correct?


	Joerg
Vladimir Murzin Jan. 18, 2017, 2:24 p.m. UTC | #2
On 18/01/17 13:47, Joerg Roedel wrote:
> On Wed, Jan 18, 2017 at 11:13:17AM +0000, Vladimir Murzin wrote:
>> Even though dma-noop-ops assumes 1:1 memory mapping DMA memory range
>> can be different to RAM. For example, ARM STM32F4 MCU offers the
>> possibility to remap SDRAM from 0xc000_0000 to 0x0 to get CPU
>> performance boost, but DMA continue to see SDRAM at 0xc000_0000. This
>> difference in mapping is handled via device-tree "dma-range" property
>> which leads to dev->dma_pfn_offset is set nonzero. To handle such
>> cases take dma_pfn_offset into account.
>>
>> Cc: Joerg Roedel <jroedel@suse.de>
>> Cc: Christian Borntraeger <borntraeger@de.ibm.com>
>> Reported-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
>> Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
>> ---
>>  lib/dma-noop.c | 8 +++++---
>>  1 file changed, 5 insertions(+), 3 deletions(-)
>>
>> diff --git a/lib/dma-noop.c b/lib/dma-noop.c
>> index 3d766e7..a14eee5 100644
>> --- a/lib/dma-noop.c
>> +++ b/lib/dma-noop.c
>> @@ -7,6 +7,7 @@
>>  #include <linux/mm.h>
>>  #include <linux/dma-mapping.h>
>>  #include <linux/scatterlist.h>
>> +#include <linux/pfn.h>
>>  
>>  static void *dma_noop_alloc(struct device *dev, size_t size,
>>  			    dma_addr_t *dma_handle, gfp_t gfp,
>> @@ -16,7 +17,8 @@ static void *dma_noop_alloc(struct device *dev, size_t size,
>>  
>>  	ret = (void *)__get_free_pages(gfp, get_order(size));
>>  	if (ret)
>> -		*dma_handle = virt_to_phys(ret);
>> +		*dma_handle = virt_to_phys(ret) - PFN_PHYS(dev->dma_pfn_offset);
>> +
> 
> If you need to do a '-' operation here, the offset is basically a
> cpu_pfn_offset for the device. Is that correct?
> 

dma_pfn_offset is calculated as PFN_DOWN(paddr - dma_addr) in
of_dma_configure(), it is why '-' is used here.

Cheers
Vladimir

> 
> 	Joerg
> 
>
Robin Murphy Jan. 18, 2017, 2:56 p.m. UTC | #3
On 18/01/17 13:47, Joerg Roedel wrote:
> On Wed, Jan 18, 2017 at 11:13:17AM +0000, Vladimir Murzin wrote:
>> Even though dma-noop-ops assumes 1:1 memory mapping DMA memory range
>> can be different to RAM. For example, ARM STM32F4 MCU offers the
>> possibility to remap SDRAM from 0xc000_0000 to 0x0 to get CPU
>> performance boost, but DMA continue to see SDRAM at 0xc000_0000. This
>> difference in mapping is handled via device-tree "dma-range" property
>> which leads to dev->dma_pfn_offset is set nonzero. To handle such
>> cases take dma_pfn_offset into account.
>>
>> Cc: Joerg Roedel <jroedel@suse.de>
>> Cc: Christian Borntraeger <borntraeger@de.ibm.com>
>> Reported-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
>> Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
>> ---
>>  lib/dma-noop.c | 8 +++++---
>>  1 file changed, 5 insertions(+), 3 deletions(-)
>>
>> diff --git a/lib/dma-noop.c b/lib/dma-noop.c
>> index 3d766e7..a14eee5 100644
>> --- a/lib/dma-noop.c
>> +++ b/lib/dma-noop.c
>> @@ -7,6 +7,7 @@
>>  #include <linux/mm.h>
>>  #include <linux/dma-mapping.h>
>>  #include <linux/scatterlist.h>
>> +#include <linux/pfn.h>
>>  
>>  static void *dma_noop_alloc(struct device *dev, size_t size,
>>  			    dma_addr_t *dma_handle, gfp_t gfp,
>> @@ -16,7 +17,8 @@ static void *dma_noop_alloc(struct device *dev, size_t size,
>>  
>>  	ret = (void *)__get_free_pages(gfp, get_order(size));
>>  	if (ret)
>> -		*dma_handle = virt_to_phys(ret);
>> +		*dma_handle = virt_to_phys(ret) - PFN_PHYS(dev->dma_pfn_offset);
>> +
> 
> If you need to do a '-' operation here, the offset is basically a
> cpu_pfn_offset for the device. Is that correct?

Effectively, yes. The value of dev->dma_pfn_offset can be thought of as
the physical (CPU) PFN to which "bus PFN" 0 (for the given device)
corresponds. On the Keystone platform which begat this machinery, the
DRAM is at 0x08_000_0000-0x09_ffff_ffff, but there is an I/O-coherent
alias of the first 2GB which appears at 0x00_8000_0000-0x00_ffff_ffff to
devices - thus on that platform 32-bit devices get a dma_mask of
0x7fff_ffff and a dma_pfn_offset of 0x7_8000_0000 >> PAGE_SHIFT, and
everything works out.

The STM32 situation is a bit funkier, as it's actually the CPU which is
making use of a DRAM alias there, but we achieve the same effect by
giving all the DMA masters a (negative) offset to compensate, such that
subtracting the offset translates addresses from the alias region back
to the "real" physical address when handed off to a DMA master.

Robin.

> 
> 
> 	Joerg
>
diff mbox

Patch

diff --git a/lib/dma-noop.c b/lib/dma-noop.c
index 3d766e7..a14eee5 100644
--- a/lib/dma-noop.c
+++ b/lib/dma-noop.c
@@ -7,6 +7,7 @@ 
 #include <linux/mm.h>
 #include <linux/dma-mapping.h>
 #include <linux/scatterlist.h>
+#include <linux/pfn.h>
 
 static void *dma_noop_alloc(struct device *dev, size_t size,
 			    dma_addr_t *dma_handle, gfp_t gfp,
@@ -16,7 +17,8 @@  static void *dma_noop_alloc(struct device *dev, size_t size,
 
 	ret = (void *)__get_free_pages(gfp, get_order(size));
 	if (ret)
-		*dma_handle = virt_to_phys(ret);
+		*dma_handle = virt_to_phys(ret) - PFN_PHYS(dev->dma_pfn_offset);
+
 	return ret;
 }
 
@@ -32,7 +34,7 @@  static dma_addr_t dma_noop_map_page(struct device *dev, struct page *page,
 				      enum dma_data_direction dir,
 				      unsigned long attrs)
 {
-	return page_to_phys(page) + offset;
+	return page_to_phys(page) + offset - PFN_PHYS(dev->dma_pfn_offset);
 }
 
 static int dma_noop_map_sg(struct device *dev, struct scatterlist *sgl, int nents,
@@ -47,7 +49,7 @@  static int dma_noop_map_sg(struct device *dev, struct scatterlist *sgl, int nent
 
 		BUG_ON(!sg_page(sg));
 		va = sg_virt(sg);
-		sg_dma_address(sg) = (dma_addr_t)virt_to_phys(va);
+		sg_dma_address(sg) = (dma_addr_t)(virt_to_phys(va) - PFN_PHYS(dev->dma_pfn_offset));
 		sg_dma_len(sg) = sg->length;
 	}