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SubjectRe: [v2] PCI: Avoid unsync of LTR mechanism configuration
Hi,

On Thu, Jan 28, 2021 at 06:05:31PM +0800, mingchuang.qiao@mediatek.com wrote:
> From: Mingchuang Qiao <mingchuang.qiao@mediatek.com>
>
> In bus scan flow, the "LTR Mechanism Enable" bit of DEVCTL2 register is
> configured in pci_configure_ltr(). If device and bridge both support LTR
> mechanism, the "LTR Mechanism Enable" bit of device and bridge will be
> enabled in DEVCTL2 register. And pci_dev->ltr_path will be set as 1.
>
> If PCIe link goes down when device resets, the "LTR Mechanism Enable" bit
> of bridge will change to 0 according to PCIe r5.0, sec 7.5.3.16. However,
> the pci_dev->ltr_path value of bridge is still 1.
>
> For following conditions, check and re-configure "LTR Mechanism Enable" bit
> of bridge to make "LTR Mechanism Enable" bit mtach ltr_path value.
> -before configuring device's LTR for hot-remove/hot-add
> -before restoring device's DEVCTL2 register when restore device state
>
> Signed-off-by: Mingchuang Qiao <mingchuang.qiao@mediatek.com>
> ---
> changes of v2
> -modify patch description
> -reconfigure bridge's LTR before restoring device DEVCTL2 register
> ---
> drivers/pci/pci.c | 25 +++++++++++++++++++++++++
> drivers/pci/probe.c | 19 ++++++++++++++++---
> 2 files changed, 41 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index b9fecc25d213..88b4eb70c252 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -1437,6 +1437,24 @@ static int pci_save_pcie_state(struct pci_dev *dev)
> return 0;
> }
>
> +static void pci_reconfigure_bridge_ltr(struct pci_dev *dev)
> +{
> +#ifdef CONFIG_PCIEASPM
> + struct pci_dev *bridge;
> + u32 ctl;
> +
> + bridge = pci_upstream_bridge(dev);
> + if (bridge && bridge->ltr_path) {
> + pcie_capability_read_dword(bridge, PCI_EXP_DEVCTL2, &ctl);
> + if (!(ctl & PCI_EXP_DEVCTL2_LTR_EN)) {
> + pci_dbg(bridge, "re-enabling LTR\n");
> + pcie_capability_set_word(bridge, PCI_EXP_DEVCTL2,
> + PCI_EXP_DEVCTL2_LTR_EN);
> + }
> + }
> +#endif
> +}
> +
> static void pci_restore_pcie_state(struct pci_dev *dev)
> {
> int i = 0;
> @@ -1447,6 +1465,13 @@ static void pci_restore_pcie_state(struct pci_dev *dev)
> if (!save_state)
> return;
>
> + /*
> + * Downstream ports reset the LTR enable bit when link goes down.
> + * Check and re-configure the bit here before restoring device.
> + * PCIe r5.0, sec 7.5.3.16.
> + */
> + pci_reconfigure_bridge_ltr(dev);
> +
> cap = (u16 *)&save_state->cap.data[0];
> pcie_capability_write_word(dev, PCI_EXP_DEVCTL, cap[i++]);
> pcie_capability_write_word(dev, PCI_EXP_LNKCTL, cap[i++]);
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 953f15abc850..4ad172517fd2 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -2132,9 +2132,22 @@ static void pci_configure_ltr(struct pci_dev *dev)
> * Complex and all intermediate Switches indicate support for LTR.
> * PCIe r4.0, sec 6.18.
> */
> - if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT ||
> - ((bridge = pci_upstream_bridge(dev)) &&
> - bridge->ltr_path)) {
> + if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT) {
> + pcie_capability_set_word(dev, PCI_EXP_DEVCTL2,
> + PCI_EXP_DEVCTL2_LTR_EN);
> + dev->ltr_path = 1;
> + return;
> + }
> +
> + bridge = pci_upstream_bridge(dev);
> + if (bridge && bridge->ltr_path) {
> + pcie_capability_read_dword(bridge, PCI_EXP_DEVCTL2, &ctl);
> + if (!(ctl & PCI_EXP_DEVCTL2_LTR_EN)) {
> + pci_dbg(bridge, "re-enabling LTR\n");
> + pcie_capability_set_word(bridge, PCI_EXP_DEVCTL2,
> + PCI_EXP_DEVCTL2_LTR_EN);
> + }
> +

Can't you use pci_reconfigure_bridge_ltr() here too?

Otherwise looks good.

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