[PATCH] PCI: xilinx-nwl: Fix ECAM programming

[PATCH] PCI: xilinx-nwl: Fix ECAM programming

[Jani Nurminen]

When PCIe has been set up by the bootloader, the ecam_size field in the
E_ECAM_CONTROL register already contains a value.

The value used to be 0xc (for 16 busses; 16 MB), but was bumped to 0x10
(for 256 busses; 256 MB) by the commit 2fccd11518f1 ("PCI: xilinx-nwl:
Modify ECAM size to enable support for 256 buses").

Regardless of what the bootloader has programmed, the driver ORs in a
new maximal value without doing a proper RMW sequence. This can lead to
problems.

For example, if the bootloader programs in 0xc and the driver uses 0x10,
the ORed result is 0x1c, which is beyond the ecam_max_size limit of 0x10
(from E_ECAM_CAPABILITIES).

Avoid the problems by doing a proper RMW.

Fixes: 2fccd11518f1 ("PCI: xilinx-nwl: Modify ECAM size to enable support for 256 buses")
Signed-off-by: Jani Nurminen <jani.nurminen@windriver.com>
---
 drivers/pci/controller/pcie-xilinx-nwl.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/controller/pcie-xilinx-nwl.c b/drivers/pci/controller/pcie-xilinx-nwl.c
index 05b8c205493c..7db2c96c6cec 100644
--- a/drivers/pci/controller/pcie-xilinx-nwl.c
+++ b/drivers/pci/controller/pcie-xilinx-nwl.c
@@ -718,9 +718,10 @@ static int nwl_pcie_bridge_init(struct nwl_pcie *pcie)
 	nwl_bridge_writel(pcie, nwl_bridge_readl(pcie, E_ECAM_CONTROL) |
 			  E_ECAM_CR_ENABLE, E_ECAM_CONTROL);
 
-	nwl_bridge_writel(pcie, nwl_bridge_readl(pcie, E_ECAM_CONTROL) |
-			  (NWL_ECAM_MAX_SIZE << E_ECAM_SIZE_SHIFT),
-			  E_ECAM_CONTROL);
+	ecam_val = nwl_bridge_readl(pcie, E_ECAM_CONTROL);
+	ecam_val &= ~E_ECAM_SIZE_LOC;
+	ecam_val |= NWL_ECAM_MAX_SIZE << E_ECAM_SIZE_SHIFT;
+	nwl_bridge_writel(pcie, ecam_val, E_ECAM_CONTROL);
 
 	nwl_bridge_writel(pcie, lower_32_bits(pcie->phys_ecam_base),
 			  E_ECAM_BASE_LO);

base-commit: 8f5ae30d69d7543eee0d70083daf4de8fe15d585
-- 
2.48.1

Re: [PATCH] PCI: xilinx-nwl: Fix ECAM programming

[Manivannan Sadhasivam]

On Fri, 12 Sep 2025 11:09:48 +0200, Jani Nurminen wrote:
> When PCIe has been set up by the bootloader, the ecam_size field in the
> E_ECAM_CONTROL register already contains a value.
> 
> The value used to be 0xc (for 16 busses; 16 MB), but was bumped to 0x10
> (for 256 busses; 256 MB) by the commit 2fccd11518f1 ("PCI: xilinx-nwl:
> Modify ECAM size to enable support for 256 buses").
> 
> [...]

Applied, thanks!

[1/1] PCI: xilinx-nwl: Fix ECAM programming
      commit: 9f0fd0b2f7a4aa1925ddfa4aed537a195879e0fa

Best regards,
-- 
Manivannan Sadhasivam <mani@kernel.org>