Re: [PATCH v5 11/14] sparc: Use physical address DMA mapping

[Marek Szyprowski]

On 17.02.2026 13:27, John Paul Adrian Glaubitz wrote:
> On Wed, 2025-10-15 at 12:12 +0300, Leon Romanovsky wrote:
>> From: Leon Romanovsky <leonro@xxxxxxxxxx>
>>
>> Convert sparc architecture DMA code to use .map_phys callback.
>>
>> Signed-off-by: Leon Romanovsky <leonro@xxxxxxxxxx>
>> ---
>>   arch/sparc/kernel/iommu.c     | 30 +++++++++++++++++-----------
>>   arch/sparc/kernel/pci_sun4v.c | 31 ++++++++++++++++++-----------
>>   arch/sparc/mm/io-unit.c       | 38 ++++++++++++++++++-----------------
>>   arch/sparc/mm/iommu.c         | 46 ++++++++++++++++++++++---------------------
>>   4 files changed, 82 insertions(+), 63 deletions(-)
>>
>> diff --git a/arch/sparc/kernel/iommu.c b/arch/sparc/kernel/iommu.c
>> index da0363692528..46ef88bc9c26 100644
>> --- a/arch/sparc/kernel/iommu.c
>> +++ b/arch/sparc/kernel/iommu.c
>> @@ -260,26 +260,35 @@ static void dma_4u_free_coherent(struct device *dev, size_t size,
>>   		free_pages((unsigned long)cpu, order);
>>   }
>>   
>> -static dma_addr_t dma_4u_map_page(struct device *dev, struct page *page,
>> -				  unsigned long offset, size_t sz,
>> -				  enum dma_data_direction direction,
>> +static dma_addr_t dma_4u_map_phys(struct device *dev, phys_addr_t phys,
>> +				  size_t sz, enum dma_data_direction direction,
>>   				  unsigned long attrs)
>>   {
>>   	struct iommu *iommu;
>>   	struct strbuf *strbuf;
>>   	iopte_t *base;
>>   	unsigned long flags, npages, oaddr;
>> -	unsigned long i, base_paddr, ctx;
>> +	unsigned long i, ctx;
>>   	u32 bus_addr, ret;
>>   	unsigned long iopte_protection;
>>   
>> +	if (unlikely(attrs & DMA_ATTR_MMIO))
>> +		/*
>> +		 * This check is included because older versions of the code
>> +		 * lacked MMIO path support, and my ability to test this path
>> +		 * is limited. However, from a software technical standpoint,
>> +		 * there is no restriction, as the following code operates
>> +		 * solely on physical addresses.
>> +		 */
>> +		goto bad_no_ctx;
>> +
>>   	iommu = dev->archdata.iommu;
>>   	strbuf = dev->archdata.stc;
>>   
>>   	if (unlikely(direction == DMA_NONE))
>>   		goto bad_no_ctx;
>>   
>> -	oaddr = (unsigned long)(page_address(page) + offset);
>> +	oaddr = (unsigned long)(phys_to_virt(phys));
>>   	npages = IO_PAGE_ALIGN(oaddr + sz) - (oaddr & IO_PAGE_MASK);
>>   	npages >>= IO_PAGE_SHIFT;
>>   
>> @@ -296,7 +305,6 @@ static dma_addr_t dma_4u_map_page(struct device *dev, struct page *page,
>>   	bus_addr = (iommu->tbl.table_map_base +
>>   		    ((base - iommu->page_table) << IO_PAGE_SHIFT));
>>   	ret = bus_addr | (oaddr & ~IO_PAGE_MASK);
>> -	base_paddr = __pa(oaddr & IO_PAGE_MASK);
>>   	if (strbuf->strbuf_enabled)
>>   		iopte_protection = IOPTE_STREAMING(ctx);
>>   	else
>> @@ -304,8 +312,8 @@ static dma_addr_t dma_4u_map_page(struct device *dev, struct page *page,
>>   	if (direction != DMA_TO_DEVICE)
>>   		iopte_protection |= IOPTE_WRITE;
>>   
>> -	for (i = 0; i < npages; i++, base++, base_paddr += IO_PAGE_SIZE)
>> -		iopte_val(*base) = iopte_protection | base_paddr;
>> +	for (i = 0; i < npages; i++, base++, phys += IO_PAGE_SIZE)
>> +		iopte_val(*base) = iopte_protection | phys;

'base_paddr' was aligned to start of a page before this patch, while 
'phys' includes the offset within a page.


Could You check if the following change fixes the issue?

diff --git a/arch/sparc/kernel/iommu.c b/arch/sparc/kernel/iommu.c
index 46ef88bc9c26..edb0ffb21e2f 100644
--- a/arch/sparc/kernel/iommu.c
+++ b/arch/sparc/kernel/iommu.c
@@ -312,6 +312,7 @@ static dma_addr_t dma_4u_map_phys(struct device 
*dev, phys_addr_t phys,
         if (direction != DMA_TO_DEVICE)
                 iopte_protection |= IOPTE_WRITE;

+       phys -= offset_in_page(phys);
         for (i = 0; i < npages; i++, base++, phys += IO_PAGE_SIZE)
                 iopte_val(*base) = iopte_protection | phys;

 >> ...

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland