On 12/10/18 9:36 PM, Kishon Vijay Abraham I wrote:
Hi,
On 27/11/18 4:39 AM, Stephen Warren wrote:
From: Stephen Warren <swarren@xxxxxxxxxx>
Some implementations of the DWC PCIe endpoint controller do not allow
access to DBI registers until the attached host has started REFCLK,
released PERST, and the endpoint driver has initialized clocking of the
DBI registers based on that. One such system is NVIDIA's T194 SoC. The
PCIe endpoint subsystem and DWC driver currently don't work on such
hardware, since they assume that all endpoint configuration can happen
at any arbitrary time.
Enhance the DWC endpoint driver to support such systems by caching all
endpoint configuration in software, and only writing the configuration
to hardware once it's been initialized. This is implemented by splitting
all endpoint controller ops into two functions; the first which simply
records/caches the desired configuration whenever called by the
associated function driver and optionally calls the second, and the
second which actually programs the configuration into hardware, which
may be called either by the first function, or later when it's known
that the DBI registers are available.
diff --git a/drivers/pci/controller/dwc/pcie-designware-ep.c b/drivers/pci/controller/dwc/pcie-designware-ep.c
+void dw_pcie_set_regs_available(struct dw_pcie *pci)
+{
When will this function be invoked? Does the wrapper get an interrupt when
refclk is enabled where this function will be invoked?
Yes, there's an IRQ from the HW that indicates when PEXRST is released.
I don't recall right now if this IRQ is something that exists for all
DWC instantiations, or is Tegra-specific.
+ struct dw_pcie_ep *ep = &(pci->ep);
+ int i;
+
+ ep->hw_regs_not_available = false;
This can race with epc_ops.
+
+ dw_pcie_ep_write_header_regs(ep);
+ for_each_set_bit(i, ep->ib_window_map, ep->num_ib_windows) {
+ dw_pcie_prog_inbound_atu(pci, i,
+ ep->cached_inbound_atus[i].bar,
+ ep->cached_inbound_atus[i].cpu_addr,
+ ep->cached_inbound_atus[i].as_type);
Depending on the context in which this function is invoked, programming
inbound/outbound ATU can also race with EPC ops.
>
+ dw_pcie_ep_set_bar_regs(ep, 0, ep->cached_inbound_atus[i].bar);
+ }
+ for_each_set_bit(i, ep->ob_window_map, ep->num_ob_windows)
+ dw_pcie_prog_outbound_atu(pci, i, PCIE_ATU_TYPE_MEM,
+ ep->cached_outbound_atus[i].addr,
+ ep->cached_outbound_atus[i].pci_addr,
+ ep->cached_outbound_atus[i].size);
+ dw_pcie_dbi_ro_wr_en(pci);
+ dw_pcie_writew_dbi(pci, PCI_MSI_FLAGS, ep->cached_msi_flags);
+ dw_pcie_writew_dbi(pci, PCI_MSIX_FLAGS, ep->cached_msix_flags);
+ dw_pcie_dbi_ro_wr_dis(pci);
IMHO we should add a new epc ops ->epc_init() which indicates if the EPC is
ready to be initialized or not. Only if the epc_init indicates it's ready to be
initialized, the endpoint function driver should go ahead with further
initialization. Or else it should wait for a notification from EPC to indicate
when it's ready to be initialized.
(Did you mean epf op or epc op?)
I'm not sure how exactly how that would work; do you want the DWC core
driver or the endpoint subsystem to poll that epc op to find out when
the HW is ready to be initialized? Or do you envisage the controller
driver still calling dw_pcie_set_regs_available() (possibly renamed),
which in turn calls ->epc_init() calls for some reason?
If you don't want to cache the endpoint configuration, perhaps you want:
a) Endpoint function doesn't pro-actively call the endpoint controller
functions to configure the endpoint.
b) When endpoint HW is ready, the relevant driver calls pci_epc_ready()
(or whatever name), which lets the core know the HW can be configured.
Perhaps this schedules a work queue item to implement locking to avoid
the races you mentioned.
c) Endpoint core calls pci_epf_init() which calls epf op ->init().
One gotcha with this approach, which the caching approach helps avoid:
Once PEXRST is released, the system must respond to PCIe enumeration
requests within 50ms. Thus, SW must very quickly respond to the IRQ
indicating PEXRST release and program the endpoint configuration into
HW. By caching the configuration in the DWC driver and
immediately/synchronously applying it in the PEXRST IRQ handler, we
reduce the number of steps and amount of code taken to program the HW,
so it should get done pretty quickly. If instead we call back into the
endpoint function driver's ->init() op, we run the risk of that op doing
other stuff besides just calling the endpoint HW configuration APIs
(e.g. perhaps the function driver defers memory buffer allocation or
IOVA programming to that ->init function) which in turns makes it much
less likely the 50ms requirement will be hit. Perhaps we can solve this
by naming the op well and providing lots of comments, but my guess is
that endpoint function authors won't notice that...
