Re: [PATCH 07/11] PCI: dwc: ep: Add a generic dw_pcie_ep_linkdown() API to handle Link Down event

Niklas Cassel
2024-03-27T18:06:36Z

Hello Mani,

On Thu, Mar 14, 2024 at 08:53:46PM +0530, Manivannan Sadhasivam wrote:
> As per the PCIe base spec r5.0, section 5.2, Link Down event can happen
> under any of the following circumstances:
>
> 1. Fundamental/Hot reset
> 2. Link disable transmission by upstream component
> 3. Moving from L2/L3 to L0
>
> In those cases, Link Down causes some non-sticky DWC registers to loose the
> state (like REBAR, etc...). So the drivers need to reinitialize them to
> function properly once the link comes back again.
>
> This is not a problem for drivers supporting PERST# IRQ, since they can
> reinitialize the registers in the PERST# IRQ callback. But for the drivers
> not supporting PERST#, there is no way they can reinitialize the registers
> other than relying on Link Down IRQ received when the link goes down. So
> let's add a DWC generic API dw_pcie_ep_linkdown() that reinitializes the
> non-sticky registers and also notifies the EPF drivers about link going
> down.
>
> This API can also be used by the drivers supporting PERST# to handle the
> scenario (2) mentioned above.
>
> NOTE: For the sake of code organization, move the dw_pcie_ep_linkup()
> definition just above dw_pcie_ep_linkdown().
>
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> ---
> drivers/pci/controller/dwc/pcie-designware-ep.c | 93 ++++++++++++++++---------
> drivers/pci/controller/dwc/pcie-designware.h | 5 ++
> 2 files changed, 67 insertions(+), 31 deletions(-)
>
> diff --git a/drivers/pci/controller/dwc/pcie-designware-ep.c b/drivers/pci/controller/dwc/pcie-designware-ep.c
> index 3893a8c1a11c..5451057ca74b 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-ep.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-ep.c
> @@ -14,18 +14,6 @@
> #include <linux/pci-epc.h>
> #include <linux/pci-epf.h>
>
> -/**
> - * dw_pcie_ep_linkup - Notify EPF drivers about link up event
> - * @ep: DWC EP device
> - */
> -void dw_pcie_ep_linkup(struct dw_pcie_ep *ep)
> -{
> - struct pci_epc *epc = ep->epc;
> -
> - pci_epc_linkup(epc);
> -}
> -EXPORT_SYMBOL_GPL(dw_pcie_ep_linkup);
> -
> /**
> * dw_pcie_ep_init_notify - Notify EPF drivers about EPC initialization
> * complete
> @@ -672,6 +660,29 @@ static unsigned int dw_pcie_ep_find_ext_capability(struct dw_pcie *pci, int cap)
> return 0;
> }
>
> +static void dw_pcie_ep_init_non_sticky_registers(struct dw_pcie *pci)
> +{
> + unsigned int offset;
> + unsigned int nbars;
> + u32 reg, i;
> +
> + offset = dw_pcie_ep_find_ext_capability(pci, PCI_EXT_CAP_ID_REBAR);
> +
> + dw_pcie_dbi_ro_wr_en(pci);
> +
> + if (offset) {
> + reg = dw_pcie_readl_dbi(pci, offset + PCI_REBAR_CTRL);
> + nbars = (reg & PCI_REBAR_CTRL_NBAR_MASK) >>
> + PCI_REBAR_CTRL_NBAR_SHIFT;
> +
> + for (i = 0; i < nbars; i++, offset += PCI_REBAR_CTRL)
> + dw_pcie_writel_dbi(pci, offset + PCI_REBAR_CAP, 0x0);
> + }
> +
> + dw_pcie_setup(pci);
> + dw_pcie_dbi_ro_wr_dis(pci);
> +}
> +
> /**
> * dw_pcie_ep_init_registers - Initialize DWC EP specific registers
> * @ep: DWC EP device
> @@ -686,13 +697,11 @@ int dw_pcie_ep_init_registers(struct dw_pcie_ep *ep)
> struct dw_pcie_ep_func *ep_func;
> struct device *dev = pci->dev;
> struct pci_epc *epc = ep->epc;
> - unsigned int offset, ptm_cap_base;
> - unsigned int nbars;
> + u32 ptm_cap_base, reg;
> u8 hdr_type;
> u8 func_no;
> - int i, ret;
> void *addr;
> - u32 reg;
> + int ret;
>
> hdr_type = dw_pcie_readb_dbi(pci, PCI_HEADER_TYPE) &
> PCI_HEADER_TYPE_MASK;
> @@ -755,20 +764,8 @@ int dw_pcie_ep_init_registers(struct dw_pcie_ep *ep)
> if (ep->ops->init)
> ep->ops->init(ep);
>
> - offset = dw_pcie_ep_find_ext_capability(pci, PCI_EXT_CAP_ID_REBAR);
> ptm_cap_base = dw_pcie_ep_find_ext_capability(pci, PCI_EXT_CAP_ID_PTM);
>
> - dw_pcie_dbi_ro_wr_en(pci);
> -
> - if (offset) {
> - reg = dw_pcie_readl_dbi(pci, offset + PCI_REBAR_CTRL);
> - nbars = (reg & PCI_REBAR_CTRL_NBAR_MASK) >>
> - PCI_REBAR_CTRL_NBAR_SHIFT;
> -
> - for (i = 0; i < nbars; i++, offset += PCI_REBAR_CTRL)
> - dw_pcie_writel_dbi(pci, offset + PCI_REBAR_CAP, 0x0);
> - }
> -
> /*
> * PTM responder capability can be disabled only after disabling
> * PTM root capability.
> @@ -785,9 +782,6 @@ int dw_pcie_ep_init_registers(struct dw_pcie_ep *ep)
> dw_pcie_dbi_ro_wr_dis(pci);
> }
>
> - dw_pcie_setup(pci);
> - dw_pcie_dbi_ro_wr_dis(pci);
> -

Your previous series had:

- dw_pcie_setup(pci);
- dw_pcie_dbi_ro_wr_dis(pci);
+ dw_pcie_ep_init_non_sticky_registers(pci);

Here.
I tested this series, but it did not work for me (the Resizable BARs did
not get resized) since you removed the call to
dw_pcie_ep_init_non_sticky_registers().

By readding the call to dw_pcie_ep_init_non_sticky_registers(),
the BARs get Resized again.

BTW do you have a git branch with both your series somewhere?
(Possibly even rebased on
https://lore.kernel.org/linux-pci/20240320113157.322695-1-cassel@kernel.org/T/#t
like you suggested in your other mail.)

Kind regards,
Niklas