linux-kernel - [PATCH 0/2] PCI: endpoint: Rework the EPC to EPF notification

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Message-Id: <20220811094237.77632-1-manivannan.sadhasivam@linaro.org>
Date:   Thu, 11 Aug 2022 15:12:35 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     kishon@...com, lpieralisi@...nel.org, bhelgaas@...gle.com
Cc:     kw@...ux.com, robh@...nel.org, vidyas@...dia.com,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Subject: [PATCH 0/2] 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.

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

Manivannan Sadhasivam (2):
  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/endpoint/functions/pci-epf-test.c | 38 ++++++-------------
 drivers/pci/endpoint/pci-epc-core.c           | 15 ++++++--
 include/linux/pci-epc.h                       |  8 ----
 include/linux/pci-epf.h                       | 19 ++++++----
 4 files changed, 36 insertions(+), 44 deletions(-)

-- 
2.25.1