Re: [PATCH v9 08/10] PCI: dwc: ep: Add a generic dw_pcie_ep_linkdown() API to handle LINK_DOWN event

[Manivannan Sadhasivam]

On Thu, Mar 07, 2024 at 10:43:19PM +0100, Niklas Cassel wrote:
> On Mon, Mar 04, 2024 at 02:52:20PM +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
> > 
> > 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@xxxxxxxxxx>
> > ---
> >  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);
> > -
> >  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);
> 
> If you look at PCI_REBAR_CAP, you will see that it is sticky,
> but you have to actually read the databook to see that:
> 
> "The RESBAR_CTRL_REG_BAR_SIZE field is automatically updated
> when you write to RESBAR_CAP_REG_0_REG through the DBI."
> 
> So the reason why we need to write this register, even though
> it is sticky, is to update the RESBAR_CTRL_REG_BAR_SIZE register,
> which is not sticky :)
> 
> (Perhaps we should add that as a comment?)
> 

Yeah, makes sense.

> 
> > +	}
> > +
> > +	/*
> > +	 * 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);
> 
> From looking at the databook:
> PCI_PTM_CAP_ROOT:
> Note: This register field is sticky.
> 
> PCI_PTM_CAP_RES:
> Note: This register field is sticky.
> 
> PCI_PTM_GRANULARITY_MASK:
> Dbi: if (DBI_RO_WR_EN == 1) then R/W(sticky) else
> R(sticky)
> 
> So all these register fields appear to be sticky to me.
> So I would assume that the PTM related writes could be
> done in dw_pcie_ep_init_registers().
> 

Sorry, I didn't cross check the registers w/ databook as I was under the
assumption that all PTM registers are non-sticky. Will move them.

- Mani

> 
> > +	}
> > +
> > +	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
> > 

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