linux-kernel - Re: [PATCH v5 0/5] PCI: endpoint: Rework the EPC to EPF notification

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Date:   Tue, 14 Feb 2023 07:51:07 +0900
From:   Krzysztof Wilczyński <kw@...ux.com>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     kishon@...nel.org, lpieralisi@...nel.org, bhelgaas@...gle.com,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        robh@...nel.org, vidyas@...dia.com, vigneshr@...com
Subject: Re: [PATCH v5 0/5] PCI: endpoint: Rework the EPC to EPF notification

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.
[...]

Applied to pci/endpoint, thank you!

[01/05] PCI: dra7xx: Use threaded IRQ handler for "dra7xx-pcie-main" IRQ
        https://git.kernel.org/pci/pci/c/da87d35a6e51

[02/05] PCI: tegra194: Move dw_pcie_ep_linkup() to threaded IRQ handler
        https://git.kernel.org/pci/pci/c/c2cc5cdda46c

[03/05] PCI: endpoint: Use a separate lock for protecting epc->pci_epf list
        https://git.kernel.org/pci/pci/c/d6dd5bafaabf

[04/05] PCI: endpoint: Use callback mechanism for passing events from EPC to EPF
        https://git.kernel.org/pci/pci/c/838125b07e77

[05/05] PCI: endpoint: Use link_up() callback in place of LINK_UP notifier
        https://git.kernel.org/pci/pci/c/f5edd8715e2e

	Krzysztof