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SubjectRe: [PATCH v4 0/5] PCI: endpoint: Rework the EPC to EPF notification
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.
>

Lorenzo, can this series be merged for v6.2 since all the patches are reviewed
now?

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@linaro.org
>
> 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
>

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