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

[Miquel Raynal <miquel.raynal@bootlin.com>]

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.


Thanks,
Miquèl