Hi Kishon, On Tue, Oct 25, 2022 at 08:20:56PM +0530, Manivannan Sadhasivam wrote: > Hello, > > During the review of the patch that fixes DBI access in PCI EP, Rob > suggested [1] using a fixed interface for passing the events from EPC to > EPF instead of the in-kernel notifiers. > > This series introduces a simple callback based mechanism for passing the > events from EPC to EPF. This interface is chosen for satisfying the below > requirements: > > 1. The notification has to reach the EPF drivers without any additional > latency. > 2. The context of the caller (EPC) needs to be preserved while passing the > notifications. > > With the existing notifier mechanism, the 1st case can be satisfied since > notifiers aren't adding any huge overhead. But the 2nd case is clearly not > satisfied, because the current atomic notifiers forces the EPF > notification context to be atomic even though the caller (EPC) may not be > in atomic context. In the notification function, the EPF drivers are > required to call several EPC APIs that might sleep and this triggers a > sleeping in atomic bug during runtime. > > The above issue could be fixed by using a blocking notifier instead of > atomic, but that proposal was not accepted either [2]. > > So instead of working around the issues within the notifiers, let's get rid > of it and use the callback mechanism. > > NOTE: DRA7xx and TEGRA194 drivers are only compile tested. Testing this series > on the real platforms is greatly appreciated. > Any feedback on this series? Thanks, Mani > Thanks, > Mani > > [1] https://lore.kernel.org/all/20220802072426.GA2494@thinkpad/T/#mfa3a5b3a9694798a562c36b228f595b6a571477d > [2] https://lore.kernel.org/all/20220228055240.24774-1-manivannan.sadhasivam@xxxxxxxxxx > > Changes in v4: > > * Added check for the presence of event_ops before involing the callbacks (Kishon) > * Added return with IRQ_WAKE_THREAD when link_up event is found in the hard irq > handler of tegra194 driver (Vidya) > * Collected review tags > > Changes in v3: > > * As Kishon spotted, fixed the DRA7xx driver and also the TEGRA194 driver to > call the LINK_UP callback in threaded IRQ handler. > > Changes in v2: > > * Introduced a new "list_lock" for protecting the epc->pci_epf list and > used it in the callback mechanism. > > Manivannan Sadhasivam (5): > PCI: dra7xx: Use threaded IRQ handler for "dra7xx-pcie-main" IRQ > PCI: tegra194: Move dw_pcie_ep_linkup() to threaded IRQ handler > PCI: endpoint: Use a separate lock for protecting epc->pci_epf list > PCI: endpoint: Use callback mechanism for passing events from EPC to > EPF > PCI: endpoint: Use link_up() callback in place of LINK_UP notifier > > drivers/pci/controller/dwc/pci-dra7xx.c | 2 +- > drivers/pci/controller/dwc/pcie-tegra194.c | 9 ++++- > drivers/pci/endpoint/functions/pci-epf-test.c | 38 ++++++------------- > drivers/pci/endpoint/pci-epc-core.c | 32 ++++++++++++---- > include/linux/pci-epc.h | 10 +---- > include/linux/pci-epf.h | 19 ++++++---- > 6 files changed, 59 insertions(+), 51 deletions(-) > > -- > 2.25.1 > -- மணிவண்ணன் சதாசிவம்
