RE: [PATCH v8 6/8] PCI: dwc: Add dw_pcie_host_ops.host_exit() callback

Hongxing Zhu
2022-04-02T03:03:12Z

> -----Original Message-----
> From: Rob Herring <robh@kernel.org>
> Sent: 2022年4月2日 4:44
> To: Hongxing Zhu <hongxing.zhu@nxp.com>
> Cc: l.stach@pengutronix.de; bhelgaas@google.com; broonie@kernel.org;
> lorenzo.pieralisi@arm.com; jingoohan1@gmail.com; festevam@gmail.com;
> francesco.dolcini@toradex.com; linux-pci@vger.kernel.org;
> linux-arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org;
> kernel@pengutronix.de; dl-linux-imx <linux-imx@nxp.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 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.
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/

>
> > 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.
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