Re: [PATCH v8 08/10] PCI: dwc: ep: Add a generic dw_pcie_ep_linkdown() API to handle LINK_DOWN event

[Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>]

On Tue, Feb 27, 2024 at 12:26:05PM -0500, Frank Li wrote:
> On Tue, Feb 27, 2024 at 06:00:24PM +0530, Manivannan Sadhasivam wrote:
> > On Mon, Feb 26, 2024 at 12:18:18PM -0500, Frank Li wrote:
> > > On Sat, Feb 24, 2024 at 12:24:14PM +0530, Manivannan Sadhasivam wrote:
> > > > The PCIe link can go to LINK_DOWN state in one of the following scenarios:
> > > > 
> > > > 1. Fundamental (PERST#)/hot/warm reset
> > > > 2. Link transition from L2/L3 to L0
> > > 
> > > From L0 to L2/l3
> > > 
> > 
> > I don't understand what you mean here. Link down won't happen while moving from
> > L0 to L2/L3, it is the opposite.
> 
> Strange, why there are not linkdown from L0 to L2/l3. But have linkdown
> from L2/l3 to L0? when linkup happen? Any document show these?
> 

Refer PCIe Spec 5.0, Figure 5-1 Link Power Management State Flow Diagram.

- Mani

> Frank
> 
> > 
> > > > 
> > > > In those cases, LINK_DOWN causes some non-sticky DWC registers to loose the
> > > > state (like REBAR, PTM_CAP 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.
> > > > 
> > > > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> > > > ---
> > > >  drivers/pci/controller/dwc/pcie-designware-ep.c | 111 ++++++++++++++----------
> > > >  drivers/pci/controller/dwc/pcie-designware.h    |   5 ++
> > > >  2 files changed, 72 insertions(+), 44 deletions(-)
> > > > 
> > > > diff --git a/drivers/pci/controller/dwc/pcie-designware-ep.c b/drivers/pci/controller/dwc/pcie-designware-ep.c
> > > > index 278bdc9b2269..fed4c2936c78 100644
> > > > --- a/drivers/pci/controller/dwc/pcie-designware-ep.c
> > > > +++ b/drivers/pci/controller/dwc/pcie-designware-ep.c
> > > > @@ -14,14 +14,6 @@
> > > >  #include <linux/pci-epc.h>
> > > >  #include <linux/pci-epf.h>
> > > >  
> > > > -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);
> > > > -
> > > 
> > > No sure why git remove this block and add these back.
> > > 
> > 
> > Because, we are adding dw_pcie_ep_linkdown() API way below and it makes sense to
> > move this API also to keep it ordered. Maybe I should've described it in commit
> > message.
> > 
> > - Mani
> > 
> > > 
> > > >  void dw_pcie_ep_init_notify(struct dw_pcie_ep *ep)
> > > >  {
> > > >  	struct pci_epc *epc = ep->epc;
> > > > @@ -603,19 +595,56 @@ 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, ptm_cap_base;
> > > > +	unsigned int nbars;
> > > > +	u32 reg, i;
> > > > +
> > > > +	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.
> > > > +	 */
> > > > +	if (ptm_cap_base) {
> > > > +		dw_pcie_dbi_ro_wr_en(pci);
> > > > +		reg = dw_pcie_readl_dbi(pci, ptm_cap_base + PCI_PTM_CAP);
> > > > +		reg &= ~PCI_PTM_CAP_ROOT;
> > > > +		dw_pcie_writel_dbi(pci, ptm_cap_base + PCI_PTM_CAP, reg);
> > > > +
> > > > +		reg = dw_pcie_readl_dbi(pci, ptm_cap_base + PCI_PTM_CAP);
> > > > +		reg &= ~(PCI_PTM_CAP_RES | PCI_PTM_GRANULARITY_MASK);
> > > > +		dw_pcie_writel_dbi(pci, ptm_cap_base + PCI_PTM_CAP, reg);
> > > > +		dw_pcie_dbi_ro_wr_dis(pci);
> > > > +	}
> > > > +
> > > > +	dw_pcie_setup(pci);
> > > > +	dw_pcie_dbi_ro_wr_dis(pci);
> > > > +}
> > > > +
> > > >  int dw_pcie_ep_init_registers(struct dw_pcie_ep *ep)
> > > >  {
> > > >  	struct dw_pcie *pci = to_dw_pcie_from_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;
> > > >  	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;
> > > > @@ -678,38 +707,7 @@ 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.
> > > > -	 */
> > > > -	if (ptm_cap_base) {
> > > > -		dw_pcie_dbi_ro_wr_en(pci);
> > > > -		reg = dw_pcie_readl_dbi(pci, ptm_cap_base + PCI_PTM_CAP);
> > > > -		reg &= ~PCI_PTM_CAP_ROOT;
> > > > -		dw_pcie_writel_dbi(pci, ptm_cap_base + PCI_PTM_CAP, reg);
> > > > -
> > > > -		reg = dw_pcie_readl_dbi(pci, ptm_cap_base + PCI_PTM_CAP);
> > > > -		reg &= ~(PCI_PTM_CAP_RES | PCI_PTM_GRANULARITY_MASK);
> > > > -		dw_pcie_writel_dbi(pci, ptm_cap_base + PCI_PTM_CAP, reg);
> > > > -		dw_pcie_dbi_ro_wr_dis(pci);
> > > > -	}
> > > > -
> > > > -	dw_pcie_setup(pci);
> > > > -	dw_pcie_dbi_ro_wr_dis(pci);
> > > > +	dw_pcie_ep_init_non_sticky_registers(pci);
> > > >  
> > > >  	return 0;
> > > >  
> > > > @@ -720,6 +718,31 @@ int dw_pcie_ep_init_registers(struct dw_pcie_ep *ep)
> > > >  }
> > > >  EXPORT_SYMBOL_GPL(dw_pcie_ep_init_registers);
> > > >  
> > > > +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);
> > > > +
> > > > +void dw_pcie_ep_linkdown(struct dw_pcie_ep *ep)
> > > > +{
> > > > +	struct dw_pcie *pci = to_dw_pcie_from_ep(ep);
> > > > +	struct pci_epc *epc = ep->epc;
> > > > +
> > > > +	/*
> > > > +	 * Initialize the non-sticky DWC registers as they would've reset post
> > > > +	 * LINK_DOWN. This is specifically needed for drivers not supporting
> > > > +	 * PERST# as they have no way to reinitialize the registers before the
> > > > +	 * link comes back again.
> > > > +	 */
> > > > +	dw_pcie_ep_init_non_sticky_registers(pci);
> > > > +
> > > > +	pci_epc_linkdown(epc);
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(dw_pcie_ep_linkdown);
> > > > +
> > > >  int dw_pcie_ep_init(struct dw_pcie_ep *ep)
> > > >  {
> > > >  	int ret;
> > > > diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
> > > > index f8e5431a207b..152969545b0a 100644
> > > > --- a/drivers/pci/controller/dwc/pcie-designware.h
> > > > +++ b/drivers/pci/controller/dwc/pcie-designware.h
> > > > @@ -668,6 +668,7 @@ static inline void __iomem *dw_pcie_own_conf_map_bus(struct pci_bus *bus,
> > > >  
> > > >  #ifdef CONFIG_PCIE_DW_EP
> > > >  void dw_pcie_ep_linkup(struct dw_pcie_ep *ep);
> > > > +void dw_pcie_ep_linkdown(struct dw_pcie_ep *ep);
> > > >  int dw_pcie_ep_init(struct dw_pcie_ep *ep);
> > > >  int dw_pcie_ep_init_registers(struct dw_pcie_ep *ep);
> > > >  void dw_pcie_ep_init_notify(struct dw_pcie_ep *ep);
> > > > @@ -688,6 +689,10 @@ static inline void dw_pcie_ep_linkup(struct dw_pcie_ep *ep)
> > > >  {
> > > >  }
> > > >  
> > > > +static inline void dw_pcie_ep_linkdown(struct dw_pcie_ep *ep)
> > > > +{
> > > > +}
> > > > +
> > > >  static inline int dw_pcie_ep_init(struct dw_pcie_ep *ep)
> > > >  {
> > > >  	return 0;
> > > > 
> > > > -- 
> > > > 2.25.1
> > > > 
> > 
> > -- 
> > மணிவண்ணன் சதாசிவம்

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