Re: [PATCH v2] PCI: dw-rockchip: Delay link training after hot reset in EP mode

[Niklas Cassel <cassel@kernel.org>]

On Tue, Jun 17, 2025 at 05:05:23PM -0500, Bjorn Helgaas wrote:
> On Tue, Jun 17, 2025 at 05:01:16PM -0500, Bjorn Helgaas wrote:
> > On Fri, Jun 13, 2025 at 12:19:09PM +0200, Niklas Cassel wrote:
> 
> Oh, and this sets PCIE_LTSSM_ENABLE_ENHANCE | PCIE_LTSSM_APP_DLY2_EN
> once at probe-time, but what about after a link-down/link-up cycle?
> 
> Don't we need to set PCIE_LTSSM_ENABLE_ENHANCE |
> PCIE_LTSSM_APP_DLY2_EN again when the link comes up so we don't have
> the same race when the link goes down again?

Nope, we don't.

To verify I used this patch:

diff --git a/drivers/pci/controller/dwc/pcie-dw-rockchip.c b/drivers/pci/controller/dwc/pcie-dw-rockchip.c
index be239254aacd..e79add5412b8 100644
--- a/drivers/pci/controller/dwc/pcie-dw-rockchip.c
+++ b/drivers/pci/controller/dwc/pcie-dw-rockchip.c
@@ -506,6 +506,8 @@ static irqreturn_t rockchip_pcie_ep_sys_irq_thread(int irq, void *arg)
        if (reg & PCIE_LINK_REQ_RST_NOT_INT) {
                dev_dbg(dev, "hot reset or link-down reset\n");
                dw_pcie_ep_linkdown(&pci->ep);
+               pr_info("PCIE_CLIENT_HOT_RESET_CTRL after reset: %#x\n",
+                       rockchip_pcie_readl_apb(rockchip, PCIE_CLIENT_HOT_RESET_CTRL));
                /* Stop delaying link training. */
                val = HIWORD_UPDATE_BIT(PCIE_LTSSM_APP_DLY2_DONE);
                rockchip_pcie_writel_apb(rockchip, val,




[   85.979567] rockchip-dw-pcie a40000000.pcie-ep: hot reset or link-down reset
[   85.980210] PCIE_CLIENT_HOT_RESET_CTRL after reset: 0x12
[   93.720413] rockchip-dw-pcie a40000000.pcie-ep: hot reset or link-down reset
[   93.721074] PCIE_CLIENT_HOT_RESET_CTRL after reset: 0x12

0x12 == bit 1 and bit 4 are set.

bit 1: app_dly2_en
bit 4: app_ltssm_enable_enhance



I also looked at the downstream driver and they also only set it once
during probe().


When running the controller EP mode, we (the Linux driver) currently never
reset the whole core after probe(), and as we can see above, the hardware
itself also does not reset the app_dly2_en bit during a hot reset signal.


Kind regards,
Niklas