On 4/11/22 16:46, Robin Murphy wrote: > Refactor the confusing logic to make it both clearer and more robust. If > the host1x parent device does have an IOMMU domain then iommu_present() > is redundantly true, while otherwise for the 32-bit DMA mask case it > still doesn't say whether the IOMMU driver actually knows about the DRM > device or not. > > Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx> > --- > > v2: Fix logic for older SoCs and clarify. > > drivers/gpu/drm/tegra/drm.c | 28 ++++++++++++++++++++-------- > 1 file changed, 20 insertions(+), 8 deletions(-) > > diff --git a/drivers/gpu/drm/tegra/drm.c b/drivers/gpu/drm/tegra/drm.c > index 9464f522e257..4f2bdab31064 100644 > --- a/drivers/gpu/drm/tegra/drm.c > +++ b/drivers/gpu/drm/tegra/drm.c > @@ -1092,6 +1092,19 @@ static bool host1x_drm_wants_iommu(struct host1x_device *dev) > struct host1x *host1x = dev_get_drvdata(dev->dev.parent); > struct iommu_domain *domain; > > + /* For starters, this is moot if no IOMMU is available */ > + if (!device_iommu_mapped(&dev->dev)) > + return false; > + > + /* > + * Tegra20 and Tegra30 don't support addressing memory beyond the > + * 32-bit boundary, so the regular GATHER opcodes will always be > + * sufficient and whether or not the host1x is attached to an IOMMU > + * doesn't matter. > + */ > + if (host1x_get_dma_mask(host1x) <= DMA_BIT_MASK(32)) > + return true; > + > /* > * If the Tegra DRM clients are backed by an IOMMU, push buffers are > * likely to be allocated beyond the 32-bit boundary if sufficient > @@ -1122,14 +1135,13 @@ static bool host1x_drm_wants_iommu(struct host1x_device *dev) > domain = iommu_get_domain_for_dev(dev->dev.parent); > > /* > - * Tegra20 and Tegra30 don't support addressing memory beyond the > - * 32-bit boundary, so the regular GATHER opcodes will always be > - * sufficient and whether or not the host1x is attached to an IOMMU > - * doesn't matter. > + * At the moment, the exact type of domain doesn't actually matter. > + * Only for 64-bit kernels might this be a managed DMA API domain, and > + * then only on newer SoCs using arm-smmu, since tegra-smmu doesn't > + * support default domains at all, and since those SoCs are the same > + * ones with extended GATHER support, even if it's a passthrough domain > + * it can still work out OK. > */ > - if (!domain && host1x_get_dma_mask(host1x) <= DMA_BIT_MASK(32)) > - return true; > - > return domain != NULL; > } > > @@ -1149,7 +1161,7 @@ static int host1x_drm_probe(struct host1x_device *dev) > goto put; > } > > - if (host1x_drm_wants_iommu(dev) && iommu_present(&platform_bus_type)) { > + if (host1x_drm_wants_iommu(dev)) { > tegra->domain = iommu_domain_alloc(&platform_bus_type); > if (!tegra->domain) { > err = -ENOMEM; Robin, thank you for the updated version. The patch looks okay to me. Reviewed-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx> A bit later I'll also will give it a test, just to be sure because we had problems with that function in the past.