linux-kernel - Re: [PATCH] Revert "PCI: dwc: Wait for link up only if link is started"

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Message-ID: <20230710170608.GA346178@rocinante>
Date:   Tue, 11 Jul 2023 02:06:08 +0900
From:   Krzysztof Wilczyński <kw@...ux.com>
To:     Ajay Agarwal <ajayagarwal@...gle.com>
Cc:     Johan Hovold <johan@...nel.org>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Bjorn Andersson <quic_bjorande@...cinc.com>,
        Sajid Dalvi <sdalvi@...gle.com>
Subject: Re: [PATCH] Revert "PCI: dwc: Wait for link up only if link is
 started"

Hello,

> > > > > Finally, note that the intel-gw driver is the only driver currently not
> > > > > providing a start_link callback and instead starts the link in its
> > > > > host_init callback, and which may avoid an additional one-second timeout
> > > > > during probe by making the link-up wait conditional. If anyone cares,
> > > > > that can be done in a follow-up patch with a proper motivation.
> > > 
> > > > The offending commit is bogus since it makes the intel-gw _special_ w.r.t
> > > > waiting for the link up. Most of the drivers call dw_pcie_host_init() during the
> > > > probe time and they all have to wait for 1 sec if the slot is empty.
> >
> > Mani, can you please explain how my commit made the intel-gw driver
> > special? The intel driver actually fails the dw_pcie_host_init if the
> > link does not come up. That was my motivation behind adding the fail
> > logic in the core driver as well.
> > > 
> > > Just to clarify, the intel-gw driver starts the link and waits for link
> > > up in its host_init() callback, which is called during probe. That wait
> > > could possibly just be dropped in favour of the one in
> > > dw_pcie_host_init() and/or the driver could be reworked to implement
> > > start_link().
> > > 
> > > Either way, the call in dw_pcie_host_init() will only add an additional
> > > 1 second delay in cases where the link did *not* come up.
> > > 
> > > > As Johan noted, intel-gw should make use of the async probe to avoid the boot
> > > > delay instead of adding a special case.
> > > 
> > > Indeed.

The whole conversation above about the intel-gw driver: would something
need to be addressed here?  Or can I pick the suggested fix?

> > My apologies for adding this regression in some of the SOCs.
> > May I suggest to keep my patch and make the following change instead?
> > This shall keep the existing behavior as is, and save the boot time
> > for drivers that do not define the start_link()?
[...]

> I just realized that Fabio pushed exactly the same patch as I suggested
> here:
> https://lore.kernel.org/all/20230704122635.1362156-1-festevam@gmail.com/.
> I think it is better we take it instead of reverting my commit.

Will do.  I will also make sure that we have correct attributions in place.

	Krzysztof