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Message-ID: <20251021020345.151202-1-cmirabil@redhat.com>
Date: Mon, 20 Oct 2025 22:03:40 -0400
From: Charles Mirabile <cmirabil@...hat.com>
To: samuel.holland@...ive.com
Cc: bhelgaas@...gle.com,
jingoohan1@...il.com,
kwilczynski@...nel.org,
linux-kernel@...r.kernel.org,
linux-pci@...r.kernel.org,
lpieralisi@...nel.org,
mani@...nel.org,
robh@...nel.org,
Charles Mirabile <cmirabil@...hat.com>
Subject: Re: [PATCH] PCI: dwc: Use multiple ATU regions for large bridge windows
Hi Samuel—
On Wed, Oct 15, 2025 at 04:15:01PM -0700, Samuel Holland wrote:
> Some SoCs may allocate more address space for a bridge window than can
> be covered by a single ATU region. Allow using a larger bridge window
> by allocating multiple adjacent ATU regions.
I had a similar patch floating around that I wanted to upstream, but I
figured I should take a look at lore before sending it in case someone
else had the same idea. Looks like great mind think alike :^). I have
attached my version the patch to this email and will leave some feedback
inline. If you want to incorporate some of my changes, feel free to add
Acked-by: Charles Mirabile <cmirabil@...hat.com>
or even a Co-developed-by and my DCO.
>
> Signed-off-by: Samuel Holland <samuel.holland@...ive.com>
> ---
> An example of where this is needed is the ESWIN EIC7700 SoC[1]. The SoC
> decodes 128 GiB of address space to the PCIe controller. Without this
> change, only 8 GiB is usable; after this change 48 GiB (6 ATU regions)
> is usable, which allows using PCIe cards with >8 GiB BARs:
>
> eic7700-pcie 54000000.pcie: host bridge /soc/pcie@...00000 ranges:
> eic7700-pcie 54000000.pcie: IO 0x0040800000..0x0040ffffff -> 0x0040800000
> eic7700-pcie 54000000.pcie: MEM 0x0041000000..0x004fffffff -> 0x0041000000
> eic7700-pcie 54000000.pcie: MEM 0x8000000000..0x89ffffffff -> 0x8000000000
> eic7700-pcie 54000000.pcie: iATU: unroll T, 8 ob, 4 ib, align 4K, limit 8G
> eic7700-pcie 54000000.pcie: PCIe Gen.2 x1 link up
> eic7700-pcie 54000000.pcie: PCI host bridge to bus 0000:00
>
> [1]: https://lore.kernel.org/linux-pci/20250923120946.1218-1-zhangsenchuan@eswincomputing.com/
>
> .../pci/controller/dwc/pcie-designware-host.c | 34 ++++++++++++-------
> 1 file changed, 22 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> index 20c9333bcb1c..148076331d7b 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> @@ -873,30 +873,40 @@ static int dw_pcie_iatu_setup(struct dw_pcie_rp *pp)
>
> i = 0;
> resource_list_for_each_entry(entry, &pp->bridge->windows) {
> + u64 total_size;
`resource_size_t` might be a better fit for this
> +
> if (resource_type(entry->res) != IORESOURCE_MEM)
> continue;
>
> - if (pci->num_ob_windows <= ++i)
> - break;
> -
> - atu.index = i;
> 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;
>
> /* Adjust iATU size if MSG TLP region was allocated before */
> if (pp->msg_res && pp->msg_res->parent == entry->res)
> - atu.size = resource_size(entry->res) -
> + total_size = resource_size(entry->res) -
> resource_size(pp->msg_res);
> else
> - atu.size = resource_size(entry->res);
> + total_size = resource_size(entry->res);
>
> - ret = dw_pcie_prog_outbound_atu(pci, &atu);
> - if (ret) {
> - dev_err(pci->dev, "Failed to set MEM range %pr\n",
> - entry->res);
> - return ret;
> - }
> + do {
> + if (pci->num_ob_windows <= ++i)
> + break;
I think it might be bad if you were to only able to partially map a given
resource. In my version, I keep the original check outside the loop with
merely `break`, but return an error from probe in this check.
> +
> + atu.index = i;
> + atu.size = min(total_size, pci->region_limit + 1);
I had to look up the difference because I couldn't remember—I used `MIN`
here instead of `min`. I think `MIN` is approriate, but I am not sure it
really matters so you could keep `min`.
> +
> + ret = dw_pcie_prog_outbound_atu(pci, &atu);
> + if (ret) {
> + dev_err(pci->dev, "Failed to set MEM range %pr\n",
> + entry->res);
> + return ret;
> + }
> +
> + atu.parent_bus_addr += atu.size;
> + atu.pci_addr += atu.size;
> + total_size -= atu.size;
> + } while (total_size);
> }
>
> if (pp->io_size) {
> --
> 2.47.2
>
> base-commit: 5a6f65d1502551f84c158789e5d89299c78907c7
> branch: up/pci-bridge-window
I also included an attempt at the inbound window version after seeing
Nilkas's feedback.
Best—Charlie
Signed-off-by: Charles Mirabile <cmirabil@...hat.com>
---
diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
index 20c9333bcb1c..f30961482799 100644
--- a/drivers/pci/controller/dwc/pcie-designware-host.c
+++ b/drivers/pci/controller/dwc/pcie-designware-host.c
@@ -873,29 +873,49 @@ static int dw_pcie_iatu_setup(struct dw_pcie_rp *pp)
i = 0;
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)
+ if (pci->num_ob_windows <= i + 1)
break;
- atu.index = i;
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;
/* Adjust iATU size if MSG TLP region was allocated before */
if (pp->msg_res && pp->msg_res->parent == entry->res)
- atu.size = resource_size(entry->res) -
+ res_size = resource_size(entry->res) -
resource_size(pp->msg_res);
else
- atu.size = resource_size(entry->res);
+ res_size = resource_size(entry->res);
+
+ while (res_size > 0) {
+ /*
+ * Make sure to fail probe if we run out of windows
+ * in the middle and we would end up only partially
+ * mapping a single resource
+ */
+ if (pci->num_ob_windows <= ++i) {
+ dev_err(pci->dev, "Exhausted outbound windows mapping %pr\n",
+ entry->res);
+ return -ENOMEM;
+ }
+ atu.index = i;
+ atu.size = MIN(pci->region_limit + 1, res_size);
- ret = dw_pcie_prog_outbound_atu(pci, &atu);
- if (ret) {
- dev_err(pci->dev, "Failed to set MEM range %pr\n",
- entry->res);
- return ret;
+ ret = dw_pcie_prog_outbound_atu(pci, &atu);
+ if (ret) {
+ dev_err(pci->dev, "Failed to set MEM range %pr\n",
+ entry->res);
+ return ret;
+ }
+
+ atu.parent_bus_addr += atu.size;
+ atu.pci_addr += atu.size;
+ res_size -= atu.size;
}
}
@@ -926,20 +946,38 @@ static int dw_pcie_iatu_setup(struct dw_pcie_rp *pp)
i = 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;
- ret = dw_pcie_prog_inbound_atu(pci, i++, PCIE_ATU_TYPE_MEM,
- entry->res->start,
- entry->res->start - entry->offset,
- resource_size(entry->res));
- if (ret) {
- dev_err(pci->dev, "Failed to set DMA range %pr\n",
- entry->res);
- return ret;
+ res_size = resource_size(entry->res);
+ res_start = entry->res->start;
+ while (res_size >= 0) {
+ /*
+ * Make sure to fail probe if we run out of windows
+ * in the middle and we would end up only partially
+ * mapping a single resource
+ */
+ if (pci->num_ib_windows <= i) {
+ dev_err(pci->dev, "Exhausted inbound windows mapping %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,
+ res_start - entry->offset, window_size);
+ if (ret) {
+ dev_err(pci->dev, "Failed to set DMA range %pr\n",
+ entry->res);
+ return ret;
+ }
+
+ res_start += window_size;
+ res_size -= window_size;
}
}
--
2.43.0
base-commit: 211ddde0823f1442e4ad052a2f30f050145ccada
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