Re: [PATCH] net: ethernet: ravb: fix dma mapping failure handling

[Nikita Yushchenko]

12.01.2024 14:56, Denis Kirjanov wrote:
> On 1/12/24 08:06, Nikita Yushchenko wrote:
> > dma_mapping_error() depends on getting full 64-bit dma_addr_t and does
> > not work correctly if 32-bit value is passed instead.
> >
> > Fix handling of dma_map_single() failures on Rx ring entries:
> > - do not store return value of dma_map_signle() in 32-bit variable,
> > - do not use dma_mapping_error() against 32-bit descriptor field when
> >    checking if unmap is needed, check for zero size instead.
>
> Hmm, something is wrong here since you're mixing DMA api and forced 32bit values.
> if dma uses 32bit addresses then dma_addr_t need only be 32 bits wide

dma_addr_t is arch-wide type and it is 64bit on arm64

Still, some devices use 32-bit dma addresses.
Proper setting of dma masks and/of configuring iommu ensures that in no error case, dma address fits 
into 32 bits.
Still, in error case dma_map_single() returns ~((dma_addr_t)0) which uses fill dma_addr_t width and gets 
corrupted if assigned to 32-bit value, then later call to dma_mapping_error() does not recognize it. The 
patch fixes exactly this issue.