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

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Date:   Tue, 14 Feb 2023 03:32:54 +0900
From:   Krzysztof Wilczyński <kw@...ux.com>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     linux-pci@...r.kernel.org, kishon@...nel.org,
        lpieralisi@...nel.org, bhelgaas@...gle.com,
        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.
> > > 
> > 
> > Lorenzo, all patches in this series got review tags. Can you please merge now?
> > 
> 
> Krzysztof, any update on this series?

Sorry for the late reply.  I just realised that my question from a few days
ago has yet to make it to the mailing list. Again, I apologise for keeping
you waiting.


Nevertheless, I was asking whether there would be any "Fixes:" tags to add
and if we should let the stable maintainers know since this fixes an issue
that might be worth back-porting to older kernels.


Let me know.  Otherwise, everything looks good!  Thank you a lot!
 
	Krzysztof