[PATCH v5 2/3] PCI: dwc: Clean up iATU index usage in dw_pcie_iatu_setup()

Niklas Cassel
2026-01-27T15:11:04Z

The current iATU index usage in dw_pcie_iatu_setup() is a mess.

For outbound address translation the index is incremented before usage.
For inbound address translation the index is incremented after usage.

Incrementing the index after usage make much more sense, and make the
index usage consistent for both outbound and inbound address translation.

Most likely, the overly complicated logic for the outbound address
translation is because the iATU at index 0 is reserved for CFG IOs
(dw_pcie_other_conf_map_bus()), however, we should be able to use the
exact same logic for the indexing of the outbound and inbound iATUs.
(Only the starting index should be different.)

Create two new variables ob_iatu_index and ib_iatu_index, which makes
it more clear from the name itself that it is a zeroes based index,
and only increment the index if the iATU configuration call succeeded.

Since we always check if there is an index available immediately before
programming the iATU, we can remove the useless "ranges exceed outbound
iATU size" warnings, as the code is already unreachable. For the same
reason, we can also remove the useless breaks outside of the while loops.

No functional changes intended.

Signed-off-by: Niklas Cassel <cassel@kernel.org>
---
.../pci/controller/dwc/pcie-designware-host.c | 59 ++++++++++---------
1 file changed, 31 insertions(+), 28 deletions(-)

diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
index d7f57d77bdf5..87e6a32dbb9a 100644
--- a/drivers/pci/controller/dwc/pcie-designware-host.c
+++ b/drivers/pci/controller/dwc/pcie-designware-host.c
@@ -892,9 +892,10 @@ static int dw_pcie_iatu_setup(struct dw_pcie_rp *pp)
struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
struct dw_pcie_ob_atu_cfg atu = { 0 };
struct resource_entry *entry;
+ int ob_iatu_index;
+ int ib_iatu_index;
int i, ret;

- /* Note the very first outbound ATU is used for CFG IOs */
if (!pci->num_ob_windows) {
dev_err(pci->dev, "No outbound iATU found\n");
return -EINVAL;
@@ -910,16 +911,18 @@ static int dw_pcie_iatu_setup(struct dw_pcie_rp *pp)
for (i = 0; i < pci->num_ib_windows; i++)
dw_pcie_disable_atu(pci, PCIE_ATU_REGION_DIR_IB, i);

- i = 0;
+ /*
+ * NOTE: For outbound address translation, outbound iATU at index 0 is
+ * reserved for CFG IOs (dw_pcie_other_conf_map_bus()), thus start at
+ * index 1.
+ */
+ ob_iatu_index = 1;
resource_list_for_each_entry(entry, &pp->bridge->windows) {
resource_size_t res_size;

if (resource_type(entry->res) != IORESOURCE_MEM)
continue;

- if (pci->num_ob_windows <= i + 1)
- break;
-
atu.type = PCIE_ATU_TYPE_MEM;
atu.parent_bus_addr = entry->res->start - pci->parent_bus_offset;
atu.pci_addr = entry->res->start - entry->offset;
@@ -937,13 +940,13 @@ static int dw_pcie_iatu_setup(struct dw_pcie_rp *pp)
* middle. Otherwise, we would end up only partially
* mapping a single resource.
*/
- if (pci->num_ob_windows <= ++i) {
- dev_err(pci->dev, "Exhausted outbound windows for region: %pr\n",
+ if (ob_iatu_index >= pci->num_ob_windows) {
+ dev_err(pci->dev, "Cannot add outbound window for region: %pr\n",
entry->res);
return -ENOMEM;
}

- atu.index = i;
+ atu.index = ob_iatu_index;
atu.size = MIN(pci->region_limit + 1, res_size);

ret = dw_pcie_prog_outbound_atu(pci, &atu);
@@ -953,6 +956,7 @@ static int dw_pcie_iatu_setup(struct dw_pcie_rp *pp)
return ret;
}

+ ob_iatu_index++;
atu.parent_bus_addr += atu.size;
atu.pci_addr += atu.size;
res_size -= atu.size;
@@ -960,8 +964,8 @@ static int dw_pcie_iatu_setup(struct dw_pcie_rp *pp)
}

if (pp->io_size) {
- if (pci->num_ob_windows > ++i) {
- atu.index = i;
+ if (ob_iatu_index < pci->num_ob_windows) {
+ atu.index = ob_iatu_index;
atu.type = PCIE_ATU_TYPE_IO;
atu.parent_bus_addr = pp->io_base - pci->parent_bus_offset;
atu.pci_addr = pp->io_bus_addr;
@@ -973,34 +977,35 @@ static int dw_pcie_iatu_setup(struct dw_pcie_rp *pp)
entry->res);
return ret;
}
+ ob_iatu_index++;
} else {
+ /*
+ * If there are not enough outbound windows to give I/O
+ * space its own iATU, the outbound iATU at index 0 will
+ * be shared between I/O space and CFG IOs, by
+ * temporarily reconfiguring the iATU to CFG space, in
+ * order to do a CFG IO, and then immediately restoring
+ * it to I/O space.
+ */
pp->cfg0_io_shared = true;
}
}

- if (pci->num_ob_windows <= i)
- dev_warn(pci->dev, "Ranges exceed outbound iATU size (%d)\n",
- pci->num_ob_windows);
-
if (pp->use_atu_msg) {
- if (pci->num_ob_windows > ++i) {
- pp->msg_atu_index = i;
- } else {
+ if (ob_iatu_index >= pci->num_ob_windows) {
dev_err(pci->dev, "Cannot add outbound window for MSG TLP\n");
return -ENOMEM;
}
+ pp->msg_atu_index = ob_iatu_index++;
}

- i = 0;
+ ib_iatu_index = 0;
resource_list_for_each_entry(entry, &pp->bridge->dma_ranges) {
resource_size_t res_start, res_size, window_size;

if (resource_type(entry->res) != IORESOURCE_MEM)
continue;

- if (pci->num_ib_windows <= i)
- break;
-
res_size = resource_size(entry->res);
res_start = entry->res->start;
while (res_size > 0) {
@@ -1009,14 +1014,15 @@ static int dw_pcie_iatu_setup(struct dw_pcie_rp *pp)
* middle. Otherwise, we would end up only partially
* mapping a single resource.
*/
- if (pci->num_ib_windows <= i) {
- dev_err(pci->dev, "Exhausted inbound windows for region: %pr\n",
+ if (ib_iatu_index >= pci->num_ib_windows) {
+ dev_err(pci->dev, "Cannot add inbound window for region: %pr\n",
entry->res);
return -ENOMEM;
}

window_size = MIN(pci->region_limit + 1, res_size);
- ret = dw_pcie_prog_inbound_atu(pci, i++, PCIE_ATU_TYPE_MEM, res_start,
+ ret = dw_pcie_prog_inbound_atu(pci, ib_iatu_index,
+ PCIE_ATU_TYPE_MEM, res_start,
res_start - entry->offset, window_size);
if (ret) {
dev_err(pci->dev, "Failed to set DMA range %pr\n",
@@ -1024,15 +1030,12 @@ static int dw_pcie_iatu_setup(struct dw_pcie_rp *pp)
return ret;
}

+ ib_iatu_index++;
res_start += window_size;
res_size -= window_size;
}
}

- if (pci->num_ib_windows <= i)
- dev_warn(pci->dev, "Dma-ranges exceed inbound iATU size (%u)\n",
- pci->num_ib_windows);
-
return 0;
}

--
2.52.0