linux-kernel - Re: [PATCH v8 6/8] PCI: dwc: Add dw_pcie_host_ops.host

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Date:   Mon, 4 Apr 2022 09:39:33 -0500
From:   Rob Herring <robh@...nel.org>
To:     Hongxing Zhu <hongxing.zhu@....com>
Cc:     "l.stach@...gutronix.de" <l.stach@...gutronix.de>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "broonie@...nel.org" <broonie@...nel.org>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
        "jingoohan1@...il.com" <jingoohan1@...il.com>,
        "festevam@...il.com" <festevam@...il.com>,
        "francesco.dolcini@...adex.com" <francesco.dolcini@...adex.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        dl-linux-imx <linux-imx@....com>
Subject: Re: [PATCH v8 6/8] PCI: dwc: Add dw_pcie_host_ops.host_exit()
 callback

On Sat, Apr 02, 2022 at 03:03:00AM +0000, Hongxing Zhu wrote:
> > -----Original Message-----
> > From: Rob Herring <robh@...nel.org>
> > Sent: 2022年4月2日 4:44
> > To: Hongxing Zhu <hongxing.zhu@....com>
> > Cc: l.stach@...gutronix.de; bhelgaas@...gle.com; broonie@...nel.org;
> > lorenzo.pieralisi@....com; jingoohan1@...il.com; festevam@...il.com;
> > francesco.dolcini@...adex.com; linux-pci@...r.kernel.org;
> > linux-arm-kernel@...ts.infradead.org; linux-kernel@...r.kernel.org;
> > kernel@...gutronix.de; dl-linux-imx <linux-imx@....com>
> > Subject: Re: [PATCH v8 6/8] PCI: dwc: Add dw_pcie_host_ops.host_exit()
> > callback
> > 
> > On Fri, Feb 25, 2022 at 11:44:25AM +0800, Richard Zhu wrote:
> > > When the link never comes up after ->host_init(), some drivers,
> > > especially those that don't support hotplug, want to turn off clocks
> > > and power supplies.
> > 
> > Isn't supporting hotplug or not a board level decision? And hotplug doesn't
> > have to mean physical plug/unplug. For example, you could have a soldered
> > down PCIe device which needs regulators, resets, clocks, etc.
> > for that device to be initialized before the link comes up. If that device is
> > handled by a module loaded some time later, then the link may be down when
> > you probe.
> > 
> > I think the way this all needs to work is with runtime PM. If that's all in place,
> > then either you shutdown clocks/power on timeout or via sysfs suspend. If
> > there's a child device, then that should prevent suspending.
> Hi Rob:
> Thanks a lot for your review comments.
> Understand what you mean.
> i.MX PCIe doesn't support hot-plug from chip design view.

The scenario I described is not hotplug.


> The ops.host_exit() callback is invoked only when the iMX PCIe driver hooked
>  callback ops->start_link return an error.
> For the platforms, that support the hot-plug feature, they can just return one
> zero from their own ops->start_link.

You cannot have a per board start_link().

> In the current situation, i.MX PCIe does just return one zero when probe failed.
> See the discussion and commit issued by Fabio below.
> https://patchwork.kernel.org/project/linux-pci/patch/1641368602-20401-6-git-send-email-hongxing.zhu@nxp.com/
> https://patchwork.ozlabs.org/project/linux-pci/patch/20220106103645.2790803-1-festevam@gmail.com/

That's a stable fix and different discussion.

> > > Add a new ->host_exit() callback in dw_pcie_host_ops so these drivers
> > > can clean up if ->host_init() fails.
> > 
> > I'm not really a fan of adding more ops nor the ops which aren't too specific
> > about what they do. 'init' and 'exit' can be anything. I'd rather see more
> > specific ops with the DWC core driver in charge of sequence of operations and
> > the state.
> Understand. 

You don't seem to...

> i.MX PCIe can't handle the error exit properly in this case by itself. So I
>  add one more ops.host_exit() in this series.
> 
> Best Regards
> Richard Zhu
> > 
> > Rob