[PATCH] ACPI/IORT: Do not blindly trust DMA masks from firmware

[Moritz Fischer]

Address issue observed on real world system with suboptimal IORT table
where DMA masks of PCI devices would get set to 0 as result.

iort_dma_setup() would query the root complex' IORT entry for a DMA
mask, and use that over the one the device has been configured with
earlier.

Ideally we want to use the minimum mask of what the IORT contains for
the root complex and what the device was configured with, but never 0.

Fixes: 5ac65e8c8941 ("ACPI/IORT: Support address size limit for root complexes")
Signed-off-by: Moritz Fischer <mdf@xxxxxxxxxx>
---
Hi all,

not sure I'm doing this right, but I think the current behavior (while a
corner case) seems to also fail for 32 bit devices if the IORT specifies
64 bit. It works on my test system now with a 32 bit device.

Open to suggestions for better solutions (and maybe the
nc_dma_get_range() should have the same sanity check?)

Thanks,
Moritz

---
 drivers/acpi/arm64/iort.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/acpi/arm64/iort.c b/drivers/acpi/arm64/iort.c
index d4eac6d7e9fb..c48eabf8c121 100644
--- a/drivers/acpi/arm64/iort.c
+++ b/drivers/acpi/arm64/iort.c
@@ -1126,6 +1126,11 @@ static int rc_dma_get_range(struct device *dev, u64 *size)
 
 	rc = (struct acpi_iort_root_complex *)node->node_data;
 
+	if (!rc->memory_address_limit) {
+		dev_warn(dev, "Root complex has broken memory_address_limit\n");
+		return -EINVAL;
+	}
+
 	*size = rc->memory_address_limit >= 64 ? U64_MAX :
 			1ULL<<rc->memory_address_limit;
 
@@ -1172,9 +1177,9 @@ void iort_dma_setup(struct device *dev, u64 *dma_addr, u64 *dma_size)
 		 */
 		end = dmaaddr + size - 1;
 		mask = DMA_BIT_MASK(ilog2(end) + 1);
-		dev->bus_dma_limit = end;
-		dev->coherent_dma_mask = mask;
-		*dev->dma_mask = mask;
+		dev->bus_dma_limit = min_not_zero(dev->bus_dma_limit, end);
+		dev->coherent_dma_mask = min_not_zero(dev->coherent_dma_mask, mask);
+		*dev->dma_mask = min_not_zero(*dev->dma_mask, mask);
 	}
 
 	*dma_addr = dmaaddr;
-- 
2.30.0