Re: [PATCH v2 3/4] PCI: dwc: Clean up iatu index usage in dw_pcie_iatu_setup()

[Niklas Cassel <cassel@kernel.org>]

On Fri, Jan 23, 2026 at 01:45:07PM +0530, Manivannan Sadhasivam wrote:
> On Thu, Jan 22, 2026 at 11:29:17PM +0100, Niklas Cassel wrote:
> > The current iatu index usage in dw_pcie_iatu_setup() is a mess.
> > 
> 
> s/iatu/iATU here and below.
> 
> > 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. For the same
> > reason, we can also remove the useless breaks outside of the while loops.
> > 
> > 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..76be24af7cfd 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;
> > +	int ib_iatu_index_to_use;
> 
> I'd prefer ob_iatu_index, ib_iatu_index

Ok.

> 
> >  	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_to_use = 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_to_use < pci->num_ob_windows)) {
> 
> 			if (ob_iatu_index >= pci->num_ob_windows) ?

Since both you and Frank have commented on this,
I guess I am the weird one.

I will change it.


> 
> > +				dev_err(pci->dev, "Cannot add outbound window for region: %pr\n",
> >  					entry->res);
> >  				return -ENOMEM;
> >  			}
> >  
> > -			atu.index = i;
> > +			atu.index = ob_iatu_index_to_use;
> >  			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_to_use++;
> >  			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_to_use < pci->num_ob_windows) {
> > +			atu.index = ob_iatu_index_to_use;
> >  			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 +977,37 @@ static int dw_pcie_iatu_setup(struct dw_pcie_rp *pp)
> >  					entry->res);
> >  				return ret;
> >  			}
> > +			ob_iatu_index_to_use++;
> >  		} 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;
> > +		if (ob_iatu_index_to_use < pci->num_ob_windows) {
> > +			pp->msg_atu_index = ob_iatu_index_to_use;
> > +			ob_iatu_index_to_use++;
> >  		} else {
> >  			dev_err(pci->dev, "Cannot add outbound window for MSG TLP\n");
> >  			return -ENOMEM;
> 
> Let's also be consistent with error checking as well:
> 
> 		if (ob_iatu_index >= pci->num_ob_windows) {
> 			dev_err();
> 			return -ENOMEM;
> 		}
> 
> 		pp->msg_atu_index = ob_iatu_index++;


Yes, I replied this to myself as well:
https://lore.kernel.org/linux-pci/aXKpHS20vHDyh4fL@ryzen/

> 
> >  		}
> >  	}
> >  
> > -	i = 0;
> > +	ib_iatu_index_to_use = 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 +1016,15 @@ 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_to_use < pci->num_ib_windows)) {
> 
> 			if (ib_iatu_index >= pci->num_ib_windows) ?

Yes, if I change it in one place, I will change it everywhere.



Kind regards,
Niklas