[PATCH v2] PCI: imx6: Keep Root Port MSI capability also for i.MX6Q

[Soeren Moch]

On the NXP i.MX6Q chipset MSIs from the endpoints won't be received by
the iMSI-RX MSI controller if the Root Port MSI capability is disabled.

Even though the Root Port MSIs won't be received by the iMSI-RX controller
due to design, this chipset has some weird hardware bug that prevents
the endpoint MSIs from reaching when the Root Port MSI capability is
disabled.

Hence, always keep the Root Port MSI capability for this chipset.

Note that by keeping Root Port MSI capability, Root Port MSIs such as AER,
PME and others won't be received by default. So users need to use
workarounds such as passing 'pcie_pme=nomsi' cmdline param.

Fixes: f5cd8a929c825 ("PCI: dwc: Remove MSI/MSIX capability for Root Port if iMSI-RX is used as MSI controller")
Cc: <stable at vger.kernel.org> # 7.0+
Signed-off-by: Soeren Moch <smoch at web.de>
Acked-by: Richard Zhu <hongxing.zhu at nxp.com>
Reviewed-by: Frank Li <Frank.Li at nxp.com>
Reviewed-by: Manivannan Sadhasivam <mani at kernel.org>
---
Cc: Manivannan Sadhasivam <mani at kernel.org>
Cc: Richard Zhu <hongxing.zhu at nxp.com>
Cc: Lucas Stach <l.stach at pengutronix.de>
Cc: Bjorn Helgaas <bhelgaas at google.com>
Cc: Frank Li <Frank.Li at nxp.com>
Cc: Fabio Estevam <festevam at gmail.com>
Cc: linux-pci at vger.kernel.org
Cc: linux-arm-kernel at lists.infradead.org
Cc: imx at lists.linux.dev
Cc: linux-kernel at vger.kernel.org

This patch is similar to
3a4e8302e72f ("PCI: imx6: Keep Root Port MSI capability with iMSI-RX to work around hardware bug")

Tested on a tbs2910 board [1]
[1] arch/arm/boot/dts/nxp/imx/imx6q-tbs2910.dts

changes in v2:
- collect a-b and r-b tags
- use correct fixes tag (Manivannan)
  (reference commit that introduced the bug, not the incomplete fix)

Since this is a fix for a regression in linux-7.0+, can this still be merged for 7.2-rcS ?
---
 drivers/pci/controller/dwc/pci-imx6.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
index 98e1db751132..8130cf93c2bb 100644
--- a/drivers/pci/controller/dwc/pci-imx6.c
+++ b/drivers/pci/controller/dwc/pci-imx6.c
@@ -1995,7 +1995,8 @@ static const struct imx_pcie_drvdata drvdata[] = {
 		.flags = IMX_PCIE_FLAG_IMX_PHY |
 			 IMX_PCIE_FLAG_SPEED_CHANGE_WORKAROUND |
 			 IMX_PCIE_FLAG_BROKEN_SUSPEND |
-			 IMX_PCIE_FLAG_SUPPORTS_SUSPEND,
+			 IMX_PCIE_FLAG_SUPPORTS_SUSPEND |
+			 IMX_PCIE_FLAG_KEEP_MSI_CAP,
 		.dbi_length = 0x200,
 		.gpr = "fsl,imx6q-iomuxc-gpr",
 		.ltssm_off = IOMUXC_GPR12,
-- 
2.43.0