Messages in this thread | | | Date | Tue, 16 Aug 2022 20:05:08 +0530 | Subject | Re: [PATCH V1] PCI: designware-ep: Fix DBI access before core init | From | Vidya Sagar <> |
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On 8/16/2022 7:45 PM, Lorenzo Pieralisi wrote: > External email: Use caution opening links or attachments > > > On Tue, Aug 02, 2022 at 07:37:38PM +0530, Manivannan Sadhasivam wrote: >> On Tue, Aug 02, 2022 at 12:54:37PM +0530, Manivannan Sadhasivam wrote: >>> On Mon, Aug 01, 2022 at 02:27:14PM -0600, Rob Herring wrote: >>>> On Sat, Jul 30, 2022 at 8:50 AM Manivannan Sadhasivam >>>> <manivannan.sadhasivam@linaro.org> wrote: >>>>> >>>>> On Fri, Jul 29, 2022 at 05:44:04PM -0500, Bjorn Helgaas wrote: >>>>>> [+cc Xiaowei (author of 6bfc9c3a2c70), Hou (author of 8bcca2658558)] >>>>>> >>>>>> On Thu, Jul 28, 2022 at 05:56:28PM +0530, Vidya Sagar wrote: >>>>>>> On 7/28/2022 3:44 AM, Bjorn Helgaas wrote: >>>>>>>> On Wed, Jun 22, 2022 at 09:31:33AM +0530, Vidya Sagar wrote: >>>>>>>>> Platforms that cannot support their core initialization without the >>>>>>>>> reference clock from the host, implement the feature 'core_init_notifier' >>>>>>>>> to indicate the DesignWare sub-system about when their core is getting >>>>>>>>> initialized. Any accesses to the core (Ex:- DBI) would result in system >>>>>>>>> hang in such systems (Ex:- tegra194). This patch moves any access to the >>>>>>>>> core to dw_pcie_ep_init_complete() API which is effectively called only >>>>>>>>> after the core initialization. >>>> >>>>>> 6) What's going on with the CORE_INIT and LINK_UP notifiers? >>>>>> dw_pcie_ep_init_notify() is only called by qcom and tegra. >>>>>> dw_pcie_ep_linkup() is only called by dra7xx, qcom, and tegra. >>>>>> As far as I can tell, nobody at all registers to handle those >>>>>> events except a test. I think it's pointless to have that code >>>>>> if nobody uses it. >>>>>> >>>>> >>>>> I have submitted an actual driver that makes use of these notifiers: >>>>> https://lore.kernel.org/lkml/20220502060611.58987-9-manivannan.sadhasivam@linaro.org/ >>>> >>>> Notifiers aren't the best interface in the kernel. I think they are >>>> best used if there's no real linkage between the sender and receiver. >>>> For an EPC and EPF that's a fixed interface, so define a proper >>>> interface. >>>> >>> >>> Fair point! The use of notifiers also suffer from an issue where the notifier >>> chain in EPC is atomic but the EPF calls some of the functions like >>> pci_epc_write_header() could potentially sleep. >>> >>> I'll try to come up with an interface. >>> >> >> I thought about using a new set of callbacks that define the EPC events and >> have the EPF drivers populate them during probe time. Like below, >> >> ``` >> diff --git a/include/linux/pci-epf.h b/include/linux/pci-epf.h >> index e03c57129ed5..45247802d6f7 100644 >> --- a/include/linux/pci-epf.h >> +++ b/include/linux/pci-epf.h >> @@ -74,6 +74,20 @@ struct pci_epf_ops { >> struct config_group *group); >> }; >> >> +/** >> + * struct pci_epf_events - Callbacks for capturing the EPC events >> + * @init_complete: Callback for the EPC initialization complete event >> + * @link_up: Callback for the EPC link up event >> + */ >> +struct pci_epc_events { >> + void (*init_complete)(struct pci_epf *epf); >> + void (*link_up)(struct pci_epf *epf); >> +}; >> + >> /** >> * struct pci_epf_driver - represents the PCI EPF driver >> * @probe: ops to perform when a new EPF device has been bound to the EPF driver >> @@ -172,6 +186,7 @@ struct pci_epf { >> unsigned int is_vf; >> unsigned long vfunction_num_map; >> struct list_head pci_vepf; >> + struct pci_epc_events *events; >> }; >> >> /** >> ``` >> >> When each of the event is received by the EPC driver, it will use the EPC API >> to call the relevant event callback for _each_ EPF. Like below: >> >> ``` >> diff --git a/drivers/pci/endpoint/pci-epc-core.c b/drivers/pci/endpoint/pci-epc-core.c >> index 6ad9b38b63a9..4b0b30b91403 100644 >> --- a/drivers/pci/endpoint/pci-epc-core.c >> +++ b/drivers/pci/endpoint/pci-epc-core.c >> @@ -724,10 +724,15 @@ EXPORT_SYMBOL_GPL(pci_epc_linkdown); >> */ >> void pci_epc_init_notify(struct pci_epc *epc) >> { >> + struct pci_epf *epf; >> + >> if (!epc || IS_ERR(epc)) >> return; >> >> - blocking_notifier_call_chain(&epc->notifier, CORE_INIT, NULL); >> + list_for_each_entry(epf, &epc->pci_epf, list) { >> + if (epf->events->init_complete) >> + epf->events->init_complete(epf); >> + } >> } >> EXPORT_SYMBOL_GPL(pci_epc_init_notify); >> ``` >> >> Does this look good to you? I can spin up an RFC series, but wanted to check the >> interface design beforehand. > > I am resuming patch reviews, have you posted a follow up ? > > Just to understand where we are with this thread and start reviewing > from there, I will update patchwork accordingly (you should add > a Link: to this thread anyway in the new series).
Manivannan posted a new patch set at https://patchwork.kernel.org/project/linux-pci/list/?series=666818 to address concerns with the notifier mechanism.
I would be sending a follow-up patch for the current patch soon.
Thanks, Vidya Sagar
> > Thanks, > Lorenzo > >> Thanks, >> Mani >> >>> Thanks, >>> Mani >>> >>>> Rob >>> >>> -- >>> மணிவண்ணன் சதாசிவம் >> >> -- >> மணிவண்ணன் சதாசிவம்
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