PCI: tegra194: Disable direct speed change for Endpoint mode

[ Upstream commit 976f676 ]

Pre-silicon simulation showed the controller operating in Endpoint mode
initiating link speed change after completing Secondary Bus Reset. Ideally,
the Root Port or the Switch Downstream Port should initiate the link speed
change post SBR, not the Endpoint.

So, as per the hardware team recommendation, disable direct speed change
for the Endpoint mode to prevent it from initiating speed change after the
physical layer link is up at Gen1, leaving speed change ownership with the
host.

Fixes: c57247f ("PCI: tegra: Add support for PCIe endpoint mode in Tegra194")
Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
Signed-off-by: Manikanta Maddireddy <mmaddireddy@nvidia.com>
[mani: commit log]
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Jon Hunter <jonathanh@nvidia.com>
Reviewed-by: Jon Hunter <jonathanh@nvidia.com>
Reviewed-by: Vidya Sagar <vidyas@nvidia.com>
Link: https://patch.msgid.link/20260324190755.1094879-8-mmaddireddy@nvidia.com
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: Vidya Sagar

drivers/pci/controller/dwc/pcie-tegra194.c

@@ -1834,6 +1834,10 @@ static void pex_ep_event_pex_rst_deassert(struct tegra_pcie_dw *pcie)
 
 	reset_control_deassert(pcie->core_rst);
 
+	val = dw_pcie_readl_dbi(pci, PCIE_LINK_WIDTH_SPEED_CONTROL);
+	val &= ~PORT_LOGIC_SPEED_CHANGE;
+	dw_pcie_writel_dbi(pci, PCIE_LINK_WIDTH_SPEED_CONTROL, val);
+
 	if (pcie->update_fc_fixup) {
 		val = dw_pcie_readl_dbi(pci, CFG_TIMER_CTRL_MAX_FUNC_NUM_OFF);
 		val |= 0x1 << CFG_TIMER_CTRL_ACK_NAK_SHIFT;