From: Jonathan Gray Subject: Re: radeondrm: fix CAFEDEAD failure during boot for old Radeons To: Mark Kettenis Cc: tbullock@comlore.com, tech@openbsd.org Date: Fri, 9 Oct 2026 00:28:58 +1100 On Thu, Oct 08, 2026 at 02:44:39PM +0200, Mark Kettenis wrote: > > Date: Thu, 8 Oct 2026 19:44:09 +1100 > > From: Jonathan Gray > > > > On Thu, Oct 08, 2026 at 12:24:06AM -0600, Ted Bullock wrote: > > > Hello, > > > > > > I think this is a plausible fix for a very longstanding bug with > > > regards to older Radeon GPUs on a variety of platforms. > > > > > > The telltale dmesg line looks something like > > > [drm] *ERROR* radeon: ring test failed (scratch(0x15E4)=0xCAFEDEAD) > > > > > > https://marc.info/?l=openbsd-bugs&m=162447131102854 > > > https://marc.info/?l=openbsd-bugs&m=177938265735653 > > > https://marc.info/?l=openbsd-misc&m=155873575216626&w=2 > > > > > > The call to the stubbed linux dma selection logic in > > > dma_addressing_limited() has been removed (always false), but according > > > to radeon_device.c, the older Radeon chips should be using the driver's > > > 32 bit DMA logic. > > > > > > /* set DMA mask. > > > * PCIE - can handle 40-bits. > > > * IGP - can handle 40-bits > > > * AGP - generally dma32 is safest > > > * PCI - dma32 for legacy pci gart, 40 bits on newer asics > > > */ > > > dma_bits = 40; > > > if (rdev->flags & RADEON_IS_AGP) > > > dma_bits = 32; > > > if ((rdev->flags & RADEON_IS_PCI) && > > > (rdev->family <= CHIP_RS740)) > > > dma_bits = 32; > > > #ifdef CONFIG_PPC64 > > > if (rdev->family == CHIP_CEDAR) > > > dma_bits = 32; > > > #endif > > > > > > I have no idea about the PPC64 flag, nor do I have one of those fancy > > > Talos machines to play around with. Since AGP is disabled by default > > > for this driver, I'm speculating we can just use the PCI logic in lieu > > > of the dma_addressing_limited() function. > > > > > > I can confirm that my Sun Blade 100 with the XVR-100 finally boots > > > without the CAFEDEAD warning in dmesg, and it also lets me enable > > > accelerated X. > > > > > > Ted > > > > The Linux documentation for dma_addressing_limited() describes it as a > > test against the amount of physical memory. > > > > The Linux function arguments are awkward to derive other types from, > > so here is a radeon specific alternative. > > > > Index: sys/dev/pci/drm/radeon/radeon.h > > =================================================================== > > RCS file: /cvs/src/sys/dev/pci/drm/radeon/radeon.h,v > > diff -u -p -r1.33 radeon.h > > --- sys/dev/pci/drm/radeon/radeon.h 9 Mar 2026 23:58:03 -0000 1.33 > > +++ sys/dev/pci/drm/radeon/radeon.h 8 Oct 2026 08:22:09 -0000 > > @@ -2326,6 +2326,7 @@ struct radeon_device { > > bus_space_tag_t memt; > > bus_dma_tag_t dmat; > > void *irqh; > > + bool dma_limited; > > > > void (*switchcb)(void *, int, int); > > void *switchcbarg; > > Index: sys/dev/pci/drm/radeon/radeon_device.c > > =================================================================== > > RCS file: /cvs/src/sys/dev/pci/drm/radeon/radeon_device.c,v > > diff -u -p -r1.34 radeon_device.c > > --- sys/dev/pci/drm/radeon/radeon_device.c 5 Oct 2026 08:14:58 -0000 1.34 > > +++ sys/dev/pci/drm/radeon/radeon_device.c 8 Oct 2026 08:25:35 -0000 > > @@ -1392,6 +1392,9 @@ int radeon_device_init(struct radeon_dev > > } > > rdev->need_swiotlb = drm_need_swiotlb(dma_bits); > > > > + if (ptoa(physmem) > (1ULL << dma_bits)) > > + rdev->dma_limited = true; > > + > > This can't be correct. The physmem variable contains the amount of > physical memory, not the address of the highest bit of RAM. > > To do this correctly, you'd need to do something like what we do in > bus_dma_init() where you set constraint.ucr_low based on dma_bits and > count the number of high pages. > > However, this check should only matter if there is no IOMMU. But > sparc64 does have an IOMMU. So what's going on here? > > Ultimately the flag ends up being passed to ttm_pool_init(). Without > the flag being set bus_dma memory allocations will be done with the > BUS_DMA_64BIT flag set. But on sparc64 this means the IOMMU gets > bypassed and DVAs have the high bit set, even if the memory itself is > below the 4G limit. This means that on sparc64 we always need to set > the dma_limited flag unless full 64-bit addresses are supported. even amdgpu is limited to 44-bit dma how about we just always return true on sparc64? Index: sys/dev/pci/drm/include/linux/dma-mapping.h =================================================================== RCS file: /cvs/src/sys/dev/pci/drm/include/linux/dma-mapping.h,v diff -u -p -r1.13 dma-mapping.h --- sys/dev/pci/drm/include/linux/dma-mapping.h 19 Aug 2026 01:34:10 -0000 1.13 +++ sys/dev/pci/drm/include/linux/dma-mapping.h 8 Oct 2026 13:18:48 -0000 @@ -43,7 +43,11 @@ dma_set_mask_and_coherent(void *dev, uin static inline bool dma_addressing_limited(void *dev) { +#ifdef __sparc64__ + return true; +#else return false; +#endif } static inline dma_addr_t