linux-kernel - Re: [PATCH 1/5] PCI: let 'pcibios_root_bridge

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Message-ID: <20211119232017.GA1981034@bhelgaas>
Date:   Fri, 19 Nov 2021 17:20:17 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Sergio Paracuellos <sergio.paracuellos@...il.com>
Cc:     linux-pci@...r.kernel.org, linux-mips@...r.kernel.org,
        tsbogend@...ha.franken.de, john@...ozen.org,
        lorenzo.pieralisi@....com, bhelgaas@...gle.com, arnd@...db.de,
        linux-kernel@...r.kernel.org,
        Thierry Reding <thierry.reding@...il.com>
Subject: Re: [PATCH 1/5] PCI: let 'pcibios_root_bridge_prepare()' access to
 'bridge->windows'

[+cc Thierry]

In subject,

  PCI: Let pcibios_root_bridge_prepare() access bridge->windows

On Mon, Nov 15, 2021 at 08:08:05AM +0100, Sergio Paracuellos wrote:
> When function 'pci_register_host_bridge()' is called, 'bridge->windows' are
> already available. However this windows are being moved temporarily from
> there. To let 'pcibios_root_bridge_prepare()' to have access to this windows
> move this windows movement after call this function. This is interesting for
> MIPS ralink mt7621 platform to be able to properly set I/O coherence units
> with this information and avoid custom MIPs code in generic PCIe controller
> drivers.
>
> Signed-off-by: Sergio Paracuellos <sergio.paracuellos@...il.com>
> ---
>  drivers/pci/probe.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 087d3658f75c..372a70efccc6 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -898,8 +898,6 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
>  
>  	bridge->bus = bus;
>  
> -	/* Temporarily move resources off the list */
> -	list_splice_init(&bridge->windows, &resources);

Arnd added this with 37d6a0a6f470 ("PCI: Add
pci_register_host_bridge() interface") [1].

I can't remember why this was done, but we did go to some trouble to
move things around, so there must have been a good reason.

Arnd or Thierry, do you remember?

>  	bus->sysdata = bridge->sysdata;
>  	bus->ops = bridge->ops;
>  	bus->number = bus->busn_res.start = bridge->busnr;
> @@ -925,6 +923,8 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
>  	if (err)
>  		goto free;
>  
> +	/* Temporarily move resources off the list */
> +	list_splice_init(&bridge->windows, &resources);
>  	err = device_add(&bridge->dev);
>  	if (err) {
>  		put_device(&bridge->dev);
> -- 
> 2.33.0
> 

[1] https://git.kernel.org/linus/37d6a0a6f470