On Wed, Apr 23, 2025 at 03:49:16PM -0500, Arnd Bergmann wrote: > On Tue, Apr 22, 2025, at 23:10, Ben Collins wrote: > > On Tue, Apr 22, 2025 at 11:25:40AM -0500, Arnd Bergmann wrote: > >> On Tue, Apr 22, 2025, at 10:56, Ben Collins wrote: > >> > >> >> > I'll check on this, but I think it's a seperate issue. The main thing > >> >> > is > >> >> > just to configure the dma hw correctly. > >> >> > >> >> I think it's still important to check this before changing the > >> >> driver: if the larger mask doesn't actually have any effect now > >> >> because the DT caps the DMA at 4GB, then it might break later > >> >> when someone adds the correct dma-ranges properties. > >> > > >> > I'm adding dma-ranges to my dt for testing. > >> > >> Ok. The other thing you can try is to printk() the dev->bus_dma_limit > >> to see if it even tries to use >32bit addressing. > > > > Did that. Every combination of IOMMU on/off and dma-ranges in my dt always > > showed bus_dma_limit as 0x0.
> There was originally a hack for powerpc that allowed DMA to be > done in the absence of a dma-ranges property in the bus node, but > limit it to 32-bit addressing for backwards compatibility, while > all other architectures should require either an empty dma-ranges > to allow full addressing or a specific translation if there is > a bus specific limit and/or offset. > > Looking at the current code I don't see that any more, so it's > possible that now any DMA is allowed even if there is no > dma-ranges property at all. It's still there. It hardcodes zone_dma_limit to 31-bits: arch/powerpc/mm/mem.c: paging_init() I'm digging into this more. I'll check back when I have a better understanding. > > As an aside, if you could give this a quick check, I can send the revised > > patch. Appreciate the feedback. > > > > https://github.com/benmcollins/linux/commit/2f2946b33294ebff2fdaae6d1eadc976147470d6 > > This looks correct to me, but I would change two things: > > - remove the debug message, which you probably left by accident > - instead of the explicit of_device_is_compatible(), change it > to use the .data field of the of_device_id table instead. Will do. -- Ben Collins https://libjwt.io https://github.com/benmcollins -- 3EC9 7598 1672 961A 1139 173A 5D5A 57C7 242B 22CF
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