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

From: Leon Romanovsky <[email-masked]>
Date: Tue, 17 Feb 2026 15:15:25 +0200

On Tue, Feb 17, 2026 at 01:55:56PM +0100, Marek Szyprowski wrote:
> 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 <[email-masked]>
> >>
> >> Convert sparc architecture DMA code to use .map_phys callback.
> >>
> >> Signed-off-by: Leon Romanovsky <[email-masked]>
> >> ---
> >>   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(-)

<...>

> >> @@ -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.

Thanks for the fix. I had assumed we needed to revert all changes in
iounit_get_area().

Thanks

> 
> 
> 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
>