Re: [PATCH 3/3] PCI: dwc: Clean up iatu index usage in dw_pcie_iatu_setup()

[Niklas Cassel <cassel@kernel.org>]

On Thu, Jan 22, 2026 at 03:44:24PM -0500, Frank Li wrote:
> On Thu, Jan 22, 2026 at 03:54:14PM +0100, Niklas Cassel wrote:
> > 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_to_use, ib_iatu_index_to_use,
> > which makes it clear from the name itself that it is the index before
> > increment.
> >
> > 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.
> >
> > Because we always check if there is an index available immediately before
> > programming the iATU, we can also remove the useless breaks outside of
> > while loop.
> 
> The condition is the same. So combine two paragraph

Sure.


> 
> >
> > Also switch to use the more logical, but equivalent check if index is
> > smaller than length, which is the most common pattern when e.g. looping
> > through an array which has length items (0 to length-1), such that it is
> > even clearer to the reader that this is a zeroes based index.
> >
> > No functional changes intended.
> >
> > Signed-off-by: Niklas Cassel <cassel@kernel.org>
> > ---
> >  .../pci/controller/dwc/pcie-designware-host.c | 59 ++++++++++---------
> >  1 file changed, 32 insertions(+), 27 deletions(-)
> >
> > diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> > index 991fe5b9a7b3..eda94db04b63 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_to_use = 0;
> > +	int ib_iatu_index_to_use = 0;
> >  	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 +911,19 @@ 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_to_use++;
> > +
> >  	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 +941,13 @@ 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_to_use < pci->num_ob_windows)) {
> 
> Is it better "if (ob_iatu_index_to_use >= pci->num_ob_windows)"

Personally, I think no, since if you look at the condition
now used (after this patch) in:

if (pp->io_size) {
	if (ob_iatu_index_to_use < pci->num_ob_windows) {
		...

if (pp->use_atu_msg) {
	if (ob_iatu_index_to_use < pci->num_ob_windows) {
		...



The difference is that
if (pp->io_size) { and
if (pp->use_atu_msg) {

only does something if (condition)

while the loops over the memory windows have:
if (!condition)
	return -ENOMEM;

For consistency, and to try to avoid this function becoming a mess again,
I think it makes sense to use the exact same condition everywhere, and
only negate the condition if needed.


Kind regards,
Niklas