Re: [PATCH v2 2/4] clk: mvebu: armada-37xx-periph: change suspend/resume time

Bjorn Helgaas
2019-06-04T20:52:46Z

On Mon, May 27, 2019 at 8:46 AM Miquel Raynal <miquel.raynal@bootlin.com> wrote:
>
> Hi Bjorn,
>
> Thanks for the feedback.
>
> Bjorn Helgaas <bhelgaas@google.com> wrote on Tue, 21 May 2019 17:43:05
> -0500:
>
> > From: Miquel Raynal <miquel.raynal@bootlin.com>
> > Date: Tue, May 21, 2019 at 8:04 AM
> > To: Michael Turquette, Stephen Boyd, Rob Herring, Mark Rutland
> > Cc: <linux-clk@vger.kernel.org>, <devicetree@vger.kernel.org>, Thomas
> > Petazzoni, Antoine Tenart, Gregory Clement, Maxime Chevallier, Nadav
> > Haklai, Bjorn Helgaas, Rafael J . Wysocki, <linux-pm@vger.kernel.org>,
> > Miquel Raynal
> >
> > > Armada 3700 PCIe IP relies on the PCIe clock managed by this
> > > driver. For reasons related to the PCI core's organization when
> > > suspending/resuming, PCI host controller drivers must reconfigure
> > > their register at suspend_noirq()/resume_noirq() which happens after
> > > suspend()/suspend_late() and before resume_early()/resume().
> >
> > "For reasons related to the PCI core's organization" manages to
> > suggest that this change wouldn't be needed if only the PCI core did
> > something differently, without actually being specific about what it
> > would need to do differently.
> >
> > Is there something the PCI core could do better to make this easier?
> > Or is it just something like "the PCI core needs to access registers
> > after suspend_late()"? You mention the host controller, but of course
> > that's not itself a PCI device, so the PCI core doesn't have much to
> > do with it directly.
>
> Actually, if I understand correctly the below commit [1] and the core
> [2] & [3], PCI device fixups can happen at any time, including at the
> _noirq phase where, obviously, the PCI controller must be already
> setup.
>
> I don't think changing this behavior is a viable solution and I would
> not see it as a "PCI core could do better" alternative.
>
> ---8<---
>
> [1]
> commit ab14d45ea58eae67c739e4ba01871cae7b6c4586
> Author: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
> Date: Tue Mar 17 15:55:45 2015 +0100
>
> PCI: mvebu: Add suspend/resume support
>
> Add suspend/resume support for the mvebu PCIe host driver. Without
> this commit, the system will panic at resume time when PCIe devices
> are connected.
>
> Note that we have to use the ->suspend_noirq() and ->resume_noirq()
> hooks, because at resume time, the PCI fixups are done at
> ->resume_noirq() time, so the PCIe controller has to be ready at
> this point.
>
> Signed-off-by: Thomas Petazzoni
> <thomas.petazzoni@free-electrons.com> Signed-off-by: Bjorn Helgaas
> <bhelgaas@google.com> Acked-by: Jason Cooper <jason@lakedaemon.net>
>
> [2] https://elixir.bootlin.com/linux/v5.2-rc1/source/drivers/pci/pci-driver.c#L1181
> [3] https://elixir.bootlin.com/linux/v5.2-rc1/source/drivers/pci/pci-driver.c#L522
>
> --->8---
>
> >
> > s/register/registers/ ?
>
> Indeed. I would like to sort out the above technical point before
> sending a v3 with this typo corrected.

I don't have anything more to contribute here; just wanted to make
sure this wasn't working around a fixable problem in PCI.

Bjorn