linux-kernel - Re: [PATCH v2] PCI: apple: Set only available ports up

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Message-ID: <ZBQu6PBvNVO1ps/A@lpieralisi>
Date:   Fri, 17 Mar 2023 10:12:08 +0100
From:   Lorenzo Pieralisi <lpieralisi@...nel.org>
To:     Janne Grunau <j@...nau.net>
Cc:     Bjorn Helgaas <helgaas@...nel.org>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Marc Zyngier <maz@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Sven Peter <sven@...npeter.dev>, linux-pci@...r.kernel.org,
        asahi@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Daire McNamara <daire.mcnamara@...rochip.com>,
        Conor Dooley <conor.dooley@...rochip.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH v2] PCI: apple: Set only available ports up

On Thu, Mar 16, 2023 at 10:22:17PM +0100, Janne Grunau wrote:
> On 2023-03-09 10:39:35 -0600, Bjorn Helgaas wrote:
> > [+cc Daire, Conor for apple/microchip use of ECAM .init() method]
> > 
> > On Thu, Mar 09, 2023 at 02:36:24PM +0100, Janne Grunau wrote:
> > > Fixes following warning inside of_irq_parse_raw() called from the common
> > > PCI device probe path.
> > > 
> > >   /soc/pcie@...000000/pci@1,0 interrupt-map failed, using interrupt-controller
> > >   WARNING: CPU: 4 PID: 252 at drivers/of/irq.c:279 of_irq_parse_raw+0x5fc/0x724
> > 
> > Based on this commit log, I assume this patch only fixes the warning,
> > and the system *works* just fine either way.  If that's the case, it's
> > debatable whether it meets the stable kernel criteria, although the
> > documented criteria are much stricter than what happens in practice.
> 
> Yes, it fixes only the warning and hides devices. The present devices 
> still work. I confused myself with the submitted M2 devicetree. It 
> missed information in the dt node of an disabled PCIe port breaking 
> probing of the pcie controller.
>  
> I agree that the Cc: stable is not necessary. Please drop it or tell me 
> to resend the change.

I think this change is not needed as it stands. If the goal is
to disable *probing* some root ports for power efficiency, we
need a different commit log altogether, see below.

> > >   ...
> > >   Call trace:
> > >    of_irq_parse_raw+0x5fc/0x724
> > >    of_irq_parse_and_map_pci+0x128/0x1d8
> > >    pci_assign_irq+0xc8/0x140
> > >    pci_device_probe+0x70/0x188
> > >    really_probe+0x178/0x418
> > >    __driver_probe_device+0x120/0x188
> > >    driver_probe_device+0x48/0x22c
> > >    __device_attach_driver+0x134/0x1d8
> > >    bus_for_each_drv+0x8c/0xd8
> > >    __device_attach+0xdc/0x1d0
> > >    device_attach+0x20/0x2c
> > >    pci_bus_add_device+0x5c/0xc0
> > >    pci_bus_add_devices+0x58/0x88
> > >    pci_host_probe+0x124/0x178
> > >    pci_host_common_probe+0x124/0x198 [pci_host_common]
> > >    apple_pcie_probe+0x108/0x16c [pcie_apple]
> > >    platform_probe+0xb4/0xdc
> > > 
> > > This became apparent after disabling unused PCIe ports in the Apple
> > > silicon device trees instead of deleting them.
> > > 
> > > Use for_each_available_child_of_node instead of for_each_child_of_node
> > > which takes the "status" property into account.
> > > 
> > > Link: https://lore.kernel.org/asahi/20230214-apple_dts_pcie_disable_unused-v1-0-5ea0d3ddcde3@jannau.net/
> > > Link: https://lore.kernel.org/asahi/1ea2107a-bb86-8c22-0bbc-82c453ab08ce@linaro.org/
> > > Fixes: 1e33888fbe44 ("PCI: apple: Add initial hardware bring-up")
> > > Cc: stable@...r.kernel.org
> > > Reviewed-by: Marc Zyngier <maz@...nel.org>
> > > Signed-off-by: Janne Grunau <j@...nau.net>
> > > ---
> > > Changes in v2:
> > > - rewritten commit message with more details and corrections
> > > - collected Marc's "Reviewed-by:"
> > > - Link to v1: https://lore.kernel.org/r/20230307-apple_pcie_disabled_ports-v1-1-b32ef91faf19@jannau.net
> > > ---
> > >  drivers/pci/controller/pcie-apple.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/pci/controller/pcie-apple.c b/drivers/pci/controller/pcie-apple.c
> > > index 66f37e403a09..f8670a032f7a 100644
> > > --- a/drivers/pci/controller/pcie-apple.c
> > > +++ b/drivers/pci/controller/pcie-apple.c
> > > @@ -783,7 +783,7 @@ static int apple_pcie_init(struct pci_config_window *cfg)
> > >  	cfg->priv = pcie;
> > >  	INIT_LIST_HEAD(&pcie->ports);
> > >  
> > > -	for_each_child_of_node(dev->of_node, of_port) {
> > > +	for_each_available_child_of_node(dev->of_node, of_port) {
> > >  		ret = apple_pcie_setup_port(pcie, of_port);
> > >  		if (ret) {
> > >  			dev_err(pcie->dev, "Port %pOF setup fail: %d\n", of_port, ret);
> > 
> > Is this change still needed after 6fffbc7ae137 ("PCI: Honor firmware's
> > device disabled status")?  This is a generic problem, and it would be
> > a lot nicer if we had a generic solution.  But I assume it *is* still
> > needed because Rob gave his Reviewed-by.
> 
> 6fffbc7ae137 avoids the warning and hides the disabled ports as well. I 
> think we want to keep this change however in the hope that avoiding the 
> port setup of disbled ports saves energy.

That's fine but the commit log must be rewritten, it is a completely
different aim than the one stated in the current commit log and it
is not stable material.

Thanks,
Lorenzo