6.15-stable review patch. If anyone has any objections, please let me know.
------------------
From: Wenbin Yao quic_wenbyao@quicinc.com
[ Upstream commit af3c6eacce0c464f28fe0e3d365b3860aba07931 ]
As per DWC PCIe registers description 4.30a, section 1.13.43, NUM_OF_LANES named as PORT_LOGIC_LINK_WIDTH in PCIe DWC driver, is referred to as the "Predetermined Number of Lanes" in PCIe r6.0, sec 4.2.7.2.1, which explains the conditions required to enter Polling.Configuration:
Next state is Polling.Configuration after at least 1024 TS1 Ordered Sets were transmitted, and all Lanes that detected a Receiver during Detect receive eight consecutive training sequences ...
Otherwise, after a 24 ms timeout the next state is:
Polling.Configuration if,
(i) Any Lane, which detected a Receiver during Detect, received eight consecutive training sequences ... and a minimum of 1024 TS1 Ordered Sets are transmitted after receiving one TS1 or TS2 Ordered Set.
And
(ii) At least a predetermined set of Lanes that detected a Receiver during Detect have detected an exit from Electrical Idle at least once since entering Polling.Active.
Note: This may prevent one or more bad Receivers or Transmitters from holding up a valid Link from being configured, and allow for additional training in Polling.Configuration. The exact set of predetermined Lanes is implementation specific.
Note: Any Lane that receives eight consecutive TS1 or TS2 Ordered Sets should have detected an exit from Electrical Idle at least once since entering Polling.Active.
In a PCIe link supporting multiple lanes, if PORT_LOGIC_LINK_WIDTH is set to lane width the hardware supports, all lanes that detect a receiver during the Detect phase must receive eight consecutive training sequences. Otherwise, LTSSM will not enter Polling.Configuration and link training will fail.
Therefore, always set PORT_LOGIC_LINK_WIDTH to 1, regardless of the number of lanes the port actually supports, to make link up more robust. This setting will not affect the intended link width if all lanes are functional. Additionally, the link can still be established with at least one lane if other lanes are faulty.
Co-developed-by: Qiang Yu quic_qianyu@quicinc.com Signed-off-by: Qiang Yu quic_qianyu@quicinc.com Signed-off-by: Wenbin Yao quic_wenbyao@quicinc.com [mani: subject change] Signed-off-by: Manivannan Sadhasivam manivannan.sadhasivam@linaro.org [bhelgaas: update PCIe spec citation, format quote] Signed-off-by: Bjorn Helgaas bhelgaas@google.com Tested-by: Niklas Cassel cassel@kernel.org Link: https://patch.msgid.link/20250422103623.462277-1-quic_wenbyao@quicinc.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/pci/controller/dwc/pcie-designware.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-)
diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c index 97d76d3dc066e..be348b341e3cf 100644 --- a/drivers/pci/controller/dwc/pcie-designware.c +++ b/drivers/pci/controller/dwc/pcie-designware.c @@ -797,22 +797,19 @@ static void dw_pcie_link_set_max_link_width(struct dw_pcie *pci, u32 num_lanes) /* Set link width speed control register */ lwsc = dw_pcie_readl_dbi(pci, PCIE_LINK_WIDTH_SPEED_CONTROL); lwsc &= ~PORT_LOGIC_LINK_WIDTH_MASK; + lwsc |= PORT_LOGIC_LINK_WIDTH_1_LANES; switch (num_lanes) { case 1: plc |= PORT_LINK_MODE_1_LANES; - lwsc |= PORT_LOGIC_LINK_WIDTH_1_LANES; break; case 2: plc |= PORT_LINK_MODE_2_LANES; - lwsc |= PORT_LOGIC_LINK_WIDTH_2_LANES; break; case 4: plc |= PORT_LINK_MODE_4_LANES; - lwsc |= PORT_LOGIC_LINK_WIDTH_4_LANES; break; case 8: plc |= PORT_LINK_MODE_8_LANES; - lwsc |= PORT_LOGIC_LINK_WIDTH_8_LANES; break; default: dev_err(pci->dev, "num-lanes %u: invalid value\n", num_lanes);