Subject: [RFC/RFT 2/2] ARM: keystone: Install hooks for dma address translation routines

From: [email-masked] (Santosh Shilimkar)
Date: Tue, 4 Feb 2014 09:30:17 -0500

On Monday 03 February 2014 09:05 PM, Olof Johansson wrote:
> Hi,
> 
> On Mon, Feb 3, 2014 at 3:28 PM, Santosh Shilimkar
> <[email-masked]> wrote:
>> Keystone platforms have their physical memory mapped at an address
>> outside the 32-bit physical range.  A Keystone machine with 16G of RAM
>> would find its memory at 0x0800000000 - 0x0bffffffff.
>> The system interconnect allows to perform DMA transfers from first 2G of
>> physical memory (0x08 0000 0000 to 08 7FFF FFFF) which aliased in
>> hardware to the 32-bit addressable space (0x80000000 - 0xffffffff),
>> because DMA HW supports only 32-bits addressing.
>>
>> Hence, add arch hooks for dma address translation routines.
>>
>> Cc: Russell King <[email-masked]>
>> Cc: Will Deacon <[email-masked]>
>> Cc: Nicolas Pitre <[email-masked]>
>> Cc: Arnd Bergmann <[email-masked]>
>> Cc: Olof Johansson <[email-masked]>
>> Signed-off-by: Grygorii Strashko <[email-masked]>
>> Signed-off-by: Santosh Shilimkar <[email-masked]>
>> ---
>>  arch/arm/mach-keystone/keystone.c |   31 +++++++++++++++++++++++++++++++
>>  1 file changed, 31 insertions(+)
>>
>> diff --git a/arch/arm/mach-keystone/keystone.c b/arch/arm/mach-keystone/keystone.c
>> index 1b43a27..54dae03 100644
>> --- a/arch/arm/mach-keystone/keystone.c
>> +++ b/arch/arm/mach-keystone/keystone.c
>> @@ -14,6 +14,7 @@
>>  #include <linux/init.h>
>>  #include <linux/of_platform.h>
>>  #include <linux/of_address.h>
>> +#include <linux/dma-mapping.h>
>>
>>  #include <asm/setup.h>
>>  #include <asm/mach/map.h>
>> @@ -53,6 +54,28 @@ static phys_addr_t keystone_virt_to_idmap(unsigned long x)
>>         return (phys_addr_t)(x) - CONFIG_PAGE_OFFSET + KEYSTONE_LOW_PHYS_START;
>>  }
>>
>> +static unsigned long keystone_dma_pfn_offset __read_mostly;
>> +
>> +static dma_addr_t keystone_pfn_to_dma(struct device *dev, unsigned long pfn)
>> +{
>> +       return PFN_PHYS(pfn - keystone_dma_pfn_offset);
>> +}
>> +
>> +static unsigned long keystone_dma_to_pfn(struct device *dev, dma_addr_t addr)
>> +{
>> +       return PFN_DOWN(addr) + keystone_dma_pfn_offset;
>> +}
>> +
>> +static void *keystone_dma_to_virt(struct device *dev, dma_addr_t addr)
>> +{
>> +       return phys_to_virt(addr + PFN_PHYS(keystone_dma_pfn_offset));
>> +}
>> +
>> +static dma_addr_t keystone_virt_to_dma(struct device *dev, void *addr)
>> +{
>> +       return virt_to_phys(addr) - PFN_PHYS(keystone_dma_pfn_offset);
>> +}
>> +
>>  static void __init keystone_init_meminfo(void)
>>  {
>>         bool lpae = IS_ENABLED(CONFIG_ARM_LPAE);
>> @@ -89,6 +112,14 @@ static void __init keystone_init_meminfo(void)
>>         /* Populate the arch idmap hook */
>>         arch_virt_to_idmap = keystone_virt_to_idmap;
>>
>> +       /* Populate the arch DMA hooks */
>> +       keystone_dma_pfn_offset = PFN_DOWN(KEYSTONE_HIGH_PHYS_START -
>> +                                          KEYSTONE_LOW_PHYS_START);
>> +       __arch_pfn_to_dma = keystone_pfn_to_dma;
>> +       __arch_dma_to_pfn = keystone_dma_to_pfn;
>> +       __arch_dma_to_virt = keystone_dma_to_virt;
>> +       __arch_virt_to_dma = keystone_virt_to_dma;
> 
> Is this truly a static window, or is it going through an IOMMU that
> just happens to have an identity mapping setup per default?
> 
Its true physical static window hardwired in Hardware. No IOMMU
involvement.

> PPC servers use "ibm,dma-window" to describe the assigned dma address
> space for busses/devices, but the window itself doesn't contain any
> information about the physical address mapping (since it goes through
> an iommu after that). It likely doesn't fit this particular use case,
> but it's something we should look at as a base in case we need to
> start looking at bindings for this instead of coding it per SoC. We'll
> know more once we've seen what a few of the implementations out there
> are.
> 
Understood.

Regards,
Santosh