Date:   Sat, 5 Nov 2022 12:23:37 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     kishon@...nel.org, lpieralisi@...nel.org, bhelgaas@...gle.com,
        kvijayab@....com
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        kw@...ux.com, robh@...nel.org, vidyas@...dia.com, vigneshr@...com
Subject: Re: [PATCH v4 0/5] PCI: endpoint: Rework the EPC to EPF notification

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@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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