Re: [PATCH v2 2/2] PCI: designware-ep: Fix the access to DBI/iATU registers before enabling controller

[Manivannan Sadhasivam]

Hi Kishon,

On Fri, Dec 03, 2021 at 10:36:00AM +0530, Kishon Vijay Abraham I wrote:
> Hi Kunihiko,
> 
> On 01/09/21 10:46 am, Kunihiko Hayashi wrote:
> > The driver using core_init_notifier, e.g. pcie-tegra194.c, runs according
> > to the following sequence:
> > 
> >     probe()
> >         dw_pcie_ep_init()
> > 
> >     bind()
> >         dw_pcie_ep_start()
> >             enable_irq()
> > 
> >     (interrupt occurred)
> >     handler()
> >         [enable controller]
> >         dw_pcie_ep_init_complete()
> >         dw_pcie_ep_init_notify()
> > 
> > After receiving an interrupt from RC, the handler enables the controller
> > and the controller registers can be accessed.
> > So accessing the registers should do in dw_pcie_ep_init_complete().
> > 
> > Currently dw_pcie_ep_init() has functions dw_iatu_detect() and
> > dw_pcie_ep_find_capability() that include accesses to DWC registers.
> > As a result, accessing the registers before enabling the controller,
> > the access will fail.
> > 
> > The function dw_pcie_ep_init() shouldn't have any access to DWC registers
> > if the controller is enabled after calling bind(). This moves access codes
> > to DBI/iATU registers and depending variables from dw_pcie_ep_init() to
> > dw_pcie_ep_init_complete().
> 
> Ideally pci_epc_create() should be the last step by the controller driver before
> handing the control to the core EPC framework. Since after this step the EPC
> framework can start invoking the epc_ops.
> 
> Here more stuff is being added to dw_pcie_ep_init_complete() which is required
> for epc_ops and this could result in aborts for platforms which does not add
> core_init_notifier.
> 

Is there a better way to handle this situation? IMO the existing situation is
messy. Assume that if EP is gonna powered separately by an independent power
rail not tied to host PCIe domain (that's the typical endpoint device usecase),
the EP driver will fail to probe due to PHY link not getting stabilized.

So ultimately the board design needs to take care of an extra logic to power the
EP device after powering the host properly and that's not ideal.

Thanks,
Mani

> Thanks,
> Kishon
> 
> > 
> > Cc: Xiaowei Bao <xiaowei.bao@xxxxxxx>
> > Cc: Vidya Sagar <vidyas@xxxxxxxxxx>
> > Fixes: 6bfc9c3a2c70 ("PCI: designware-ep: Move the function of getting MSI capability forward")
> > Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@xxxxxxxxxxxxx>
> > Acked-by: Om Prakash Singh <omp@xxxxxxxxxx>
> > Reviewed-by: Vidya Sagar <vidyas@xxxxxxxxxx>
> > ---
> >  drivers/pci/controller/dwc/pcie-designware-ep.c | 81 +++++++++++++------------
> >  1 file changed, 41 insertions(+), 40 deletions(-)
> > 
> > diff --git a/drivers/pci/controller/dwc/pcie-designware-ep.c b/drivers/pci/controller/dwc/pcie-designware-ep.c
> > index 998b698..00ce83c 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware-ep.c
> > +++ b/drivers/pci/controller/dwc/pcie-designware-ep.c
> > @@ -636,16 +636,56 @@ static unsigned int dw_pcie_ep_find_ext_capability(struct dw_pcie *pci, int cap)
> >  int dw_pcie_ep_init_complete(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;
> >  	unsigned int offset;
> >  	unsigned int nbars;
> >  	u8 hdr_type;
> > +	u8 func_no;
> > +	void *addr;
> >  	u32 reg;
> >  	int i;
> >  
> > +	dw_pcie_iatu_detect(pci);
> > +
> > +	ep->ib_window_map = devm_kcalloc(dev,
> > +					 BITS_TO_LONGS(pci->num_ib_windows),
> > +					 sizeof(long),
> > +					 GFP_KERNEL);
> > +	if (!ep->ib_window_map)
> > +		return -ENOMEM;
> > +
> > +	ep->ob_window_map = devm_kcalloc(dev,
> > +					 BITS_TO_LONGS(pci->num_ob_windows),
> > +					 sizeof(long),
> > +					 GFP_KERNEL);
> > +	if (!ep->ob_window_map)
> > +		return -ENOMEM;
> > +
> > +	addr = devm_kcalloc(dev, pci->num_ob_windows, sizeof(phys_addr_t),
> > +			    GFP_KERNEL);
> > +	if (!addr)
> > +		return -ENOMEM;
> > +	ep->outbound_addr = addr;
> > +
> > +	for (func_no = 0; func_no < ep->epc->max_functions; func_no++) {
> > +		ep_func = devm_kzalloc(dev, sizeof(*ep_func), GFP_KERNEL);
> > +		if (!ep_func)
> > +			return -ENOMEM;
> > +
> > +		ep_func->func_no = func_no;
> > +		ep_func->msi_cap = dw_pcie_ep_find_capability(ep, func_no,
> > +							      PCI_CAP_ID_MSI);
> > +		ep_func->msix_cap = dw_pcie_ep_find_capability(ep, func_no,
> > +							       PCI_CAP_ID_MSIX);
> > +
> > +		list_add_tail(&ep_func->list, &ep->func_list);
> > +	}
> > +
> >  	hdr_type = dw_pcie_readb_dbi(pci, PCI_HEADER_TYPE) &
> >  		   PCI_HEADER_TYPE_MASK;
> >  	if (hdr_type != PCI_HEADER_TYPE_NORMAL) {
> > -		dev_err(pci->dev,
> > +		dev_err(dev,
> >  			"PCIe controller is not set to EP mode (hdr_type:0x%x)!\n",
> >  			hdr_type);
> >  		return -EIO;
> > @@ -674,8 +714,6 @@ EXPORT_SYMBOL_GPL(dw_pcie_ep_init_complete);
> >  int dw_pcie_ep_init(struct dw_pcie_ep *ep)
> >  {
> >  	int ret;
> > -	void *addr;
> > -	u8 func_no;
> >  	struct resource *res;
> >  	struct pci_epc *epc;
> >  	struct dw_pcie *pci = to_dw_pcie_from_ep(ep);
> > @@ -683,7 +721,6 @@ int dw_pcie_ep_init(struct dw_pcie_ep *ep)
> >  	struct platform_device *pdev = to_platform_device(dev);
> >  	struct device_node *np = dev->of_node;
> >  	const struct pci_epc_features *epc_features;
> > -	struct dw_pcie_ep_func *ep_func;
> >  
> >  	INIT_LIST_HEAD(&ep->func_list);
> >  
> > @@ -705,8 +742,6 @@ int dw_pcie_ep_init(struct dw_pcie_ep *ep)
> >  		}
> >  	}
> >  
> > -	dw_pcie_iatu_detect(pci);
> > -
> >  	res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "addr_space");
> >  	if (!res)
> >  		return -EINVAL;
> > @@ -714,26 +749,6 @@ int dw_pcie_ep_init(struct dw_pcie_ep *ep)
> >  	ep->phys_base = res->start;
> >  	ep->addr_size = resource_size(res);
> >  
> > -	ep->ib_window_map = devm_kcalloc(dev,
> > -					 BITS_TO_LONGS(pci->num_ib_windows),
> > -					 sizeof(long),
> > -					 GFP_KERNEL);
> > -	if (!ep->ib_window_map)
> > -		return -ENOMEM;
> > -
> > -	ep->ob_window_map = devm_kcalloc(dev,
> > -					 BITS_TO_LONGS(pci->num_ob_windows),
> > -					 sizeof(long),
> > -					 GFP_KERNEL);
> > -	if (!ep->ob_window_map)
> > -		return -ENOMEM;
> > -
> > -	addr = devm_kcalloc(dev, pci->num_ob_windows, sizeof(phys_addr_t),
> > -			    GFP_KERNEL);
> > -	if (!addr)
> > -		return -ENOMEM;
> > -	ep->outbound_addr = addr;
> > -
> >  	if (pci->link_gen < 1)
> >  		pci->link_gen = of_pci_get_max_link_speed(np);
> >  
> > @@ -750,20 +765,6 @@ int dw_pcie_ep_init(struct dw_pcie_ep *ep)
> >  	if (ret < 0)
> >  		epc->max_functions = 1;
> >  
> > -	for (func_no = 0; func_no < epc->max_functions; func_no++) {
> > -		ep_func = devm_kzalloc(dev, sizeof(*ep_func), GFP_KERNEL);
> > -		if (!ep_func)
> > -			return -ENOMEM;
> > -
> > -		ep_func->func_no = func_no;
> > -		ep_func->msi_cap = dw_pcie_ep_find_capability(ep, func_no,
> > -							      PCI_CAP_ID_MSI);
> > -		ep_func->msix_cap = dw_pcie_ep_find_capability(ep, func_no,
> > -							       PCI_CAP_ID_MSIX);
> > -
> > -		list_add_tail(&ep_func->list, &ep->func_list);
> > -	}
> > -
> >  	if (ep->ops->ep_init)
> >  		ep->ops->ep_init(ep);
> >  
> >