Re: [PATCH] ACPI/IORT: Support address size limit for root complexes

[Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>]

[+Catalin, Will]

On Mon, Jul 16, 2018 at 04:34:51PM +0100, Robin Murphy wrote:
> On 2018-07-16 4:10 PM, Lorenzo Pieralisi wrote:
> >On Tue, Jul 10, 2018 at 05:13:45PM +0100, Robin Murphy wrote:
> >>IORT revision D allows PCI root complex nodes to specify a memory
> >>address size limit equivalently to named components, to help describe
> >>straightforward integrations which don't really warrant a full-blown
> >>_DMA method. Now that our headers are up-to-date, plumb it in.
> >>
> >>Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> >>---
> >>  drivers/acpi/arm64/iort.c | 25 +++++++++++++++++++++++--
> >>  1 file changed, 23 insertions(+), 2 deletions(-)
> >>
> >>diff --git a/drivers/acpi/arm64/iort.c b/drivers/acpi/arm64/iort.c
> >>index 7a3a541046ed..4a66896e2aa3 100644
> >>--- a/drivers/acpi/arm64/iort.c
> >>+++ b/drivers/acpi/arm64/iort.c
> >>@@ -947,6 +947,24 @@ static int nc_dma_get_range(struct device *dev, u64 *size)
> >>  	return 0;
> >>  }
> >>+static int rc_dma_get_range(struct device *dev, u64 *size)
> >>+{
> >>+	struct acpi_iort_node *node;
> >>+	struct acpi_iort_root_complex *rc;
> >>+
> >>+	node = iort_scan_node(ACPI_IORT_NODE_PCI_ROOT_COMPLEX,
> >>+			      iort_match_node_callback, dev);
> >>+	if (!node || node->revision < 1)
> >>+		return -ENODEV;
> >>+
> >>+	rc = (struct acpi_iort_root_complex *)node->node_data;
> >>+
> >>+	*size = rc->memory_address_limit >= 64 ? U64_MAX :
> >>+			1ULL<<rc->memory_address_limit;
> >>+
> >>+	return 0;
> >>+}
> >>+
> >>  /**
> >>   * iort_dma_setup() - Set-up device DMA parameters.
> >>   *
> >>@@ -975,10 +993,13 @@ void iort_dma_setup(struct device *dev, u64 *dma_addr, u64 *dma_size)
> >>  	size = max(dev->coherent_dma_mask, dev->coherent_dma_mask + 1);
> >>-	if (dev_is_pci(dev))
> >>+	if (dev_is_pci(dev)) {
> >>  		ret = acpi_dma_get_range(dev, &dmaaddr, &offset, &size);
> >>-	else
> >>+		if (ret == -ENODEV)
> >>+			ret = rc_dma_get_range(dev, &size);
> >
> >Thank you for putting together the patch.
> >
> >The question is whether it is OK to ignore the IORT address limits
> >when _DMA is actually specified. It is a sort of grey area that
> >has to be clarified, maybe we can add a check to detect a size
> >mismatch, I do not know if something should be added at IORT spec
> >level to clarify its relation to the _DMA object, if present.
> 
> Yeah, I'm assuming that _DMA would be used to describe conditions
> more specific than the simple address size limit (i.e. bridge
> windows), so even if both are present, the range inferred from _DMA
> will always be less than or equal to that inferred from IORT, and
> thus rather than explicitly calculating the intersection of the two
> we can simply do this short-circuit.
> 
> If IORT accurately reflects the total number of usable address bits,
> then I can't see that it would ever make sense for _DMA to specify
> an address range which exceeds that; I guess it comes down to how
> much effort we want to spend verifying firmware instead of trusting
> it.

I agree with this reasoning and the patch looks fine, I have not
queued anything for this cycle for IORT so I would ask Will/Catalin
to pick it up (if we still have time for v4.19):

Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>