[PATCH v4 1/5] PCI: dwc: ep: iATU registers must be written after the BAR_MASK

[Niklas Cassel <cassel@kernel.org>]

The DWC Databook description for the LWR_TARGET_RW and LWR_TARGET_HW fields
in the IATU_LWR_TARGET_ADDR_OFF_INBOUND_i registers state that:
"Field size depends on log2(BAR_MASK+1) in BAR match mode."

I.e. only the upper bits are writable, and the number of writable bits is
dependent on the configured BAR_MASK.

If we do not write the BAR_MASK before writing the iATU registers, we are
relying the reset value of the BAR_MASK being larger than the requested
size of the first set_bar() call. The reset value of the BAR_MASK is SoC
dependent.

Thus, if the first set_bar() call requests a size that is larger than the
reset value of the BAR_MASK, the iATU will try to write to read-only bits,
which will cause the iATU to end up redirecting to a physical address that
is different from the address that was intended.

Thus, we should always write the iATU registers after writing the BAR_MASK.

Since set_bar() supports dynamically changing the physical address of a
BAR, this change is slightly bigger than a single line change.

While at it, add comments which clarifies the support for dynamically
changing the physical address of a BAR. (Which was previously missing.)

Fixes: f8aed6ec624f ("PCI: dwc: designware: Add EP mode support")
Signed-off-by: Niklas Cassel <cassel@kernel.org>
---
 .../pci/controller/dwc/pcie-designware-ep.c   | 46 ++++++++++++++-----
 1 file changed, 34 insertions(+), 12 deletions(-)

diff --git a/drivers/pci/controller/dwc/pcie-designware-ep.c b/drivers/pci/controller/dwc/pcie-designware-ep.c
index 507e40bd18c8..34d60142ffb5 100644
--- a/drivers/pci/controller/dwc/pcie-designware-ep.c
+++ b/drivers/pci/controller/dwc/pcie-designware-ep.c
@@ -222,19 +222,30 @@ static int dw_pcie_ep_set_bar(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
 	if ((flags & PCI_BASE_ADDRESS_MEM_TYPE_64) && (bar & 1))
 		return -EINVAL;
 
-	reg = PCI_BASE_ADDRESS_0 + (4 * bar);
-
-	if (!(flags & PCI_BASE_ADDRESS_SPACE))
-		type = PCIE_ATU_TYPE_MEM;
-	else
-		type = PCIE_ATU_TYPE_IO;
+	/*
+	 * Certain EPF drivers dynamically change the physical address of a BAR
+	 * (i.e. they call set_bar() twice, without ever calling clear_bar(), as
+	 * calling clear_bar() would clear the BAR's PCI address assigned by the
+	 * host).
+	 */
+	if (ep->epf_bar[bar]) {
+		/*
+		 * We can only dynamically change a BAR if the new configuration
+		 * doesn't fundamentally differ from the existing configuration.
+		 */
+		if (ep->epf_bar[bar]->barno != bar ||
+		    ep->epf_bar[bar]->size != size ||
+		    ep->epf_bar[bar]->flags != flags)
+			return -EINVAL;
 
-	ret = dw_pcie_ep_inbound_atu(ep, func_no, type, epf_bar->phys_addr, bar);
-	if (ret)
-		return ret;
+		/*
+		 * When dynamically changing a BAR, skip writing the BAR reg, as
+		 * that would clear the BAR's PCI address assigned by the host.
+		 */
+		goto config_atu;
+	}
 
-	if (ep->epf_bar[bar])
-		return 0;
+	reg = PCI_BASE_ADDRESS_0 + (4 * bar);
 
 	dw_pcie_dbi_ro_wr_en(pci);
 
@@ -246,9 +257,20 @@ static int dw_pcie_ep_set_bar(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
 		dw_pcie_ep_writel_dbi(ep, func_no, reg + 4, 0);
 	}
 
-	ep->epf_bar[bar] = epf_bar;
 	dw_pcie_dbi_ro_wr_dis(pci);
 
+config_atu:
+	if (!(flags & PCI_BASE_ADDRESS_SPACE))
+		type = PCIE_ATU_TYPE_MEM;
+	else
+		type = PCIE_ATU_TYPE_IO;
+
+	ret = dw_pcie_ep_inbound_atu(ep, func_no, type, epf_bar->phys_addr, bar);
+	if (ret)
+		return ret;
+
+	ep->epf_bar[bar] = epf_bar;
+
 	return 0;
 }
 
-- 
2.47.0