linux-kernel - Re: [RFC v5 1/8] PCI: Introduce domain_nr in pci_host

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Message-ID: <20210720224925.GA137627@bjorn-Precision-5520>
Date:   Tue, 20 Jul 2021 17:49:25 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Boqun Feng <boqun.feng@...il.com>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>, Arnd Bergmann <arnd@...db.de>,
        Marc Zyngier <maz@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-hyperv@...r.kernel.org, linux-pci@...r.kernel.org,
        Sunil Muthuswamy <sunilmut@...rosoft.com>,
        Mike Rapoport <rppt@...nel.org>
Subject: Re: [RFC v5 1/8] PCI: Introduce domain_nr in pci_host_bridge

On Tue, Jul 20, 2021 at 09:44:22PM +0800, Boqun Feng wrote:
> Currently we retrieve the PCI domain number of the host bridge from the
> bus sysdata (or pci_config_window if PCI_DOMAINS_GENERIC=y). Actually
> we have the information at PCI host bridge probing time, and it makes
> sense that we store it into pci_host_bridge. One benefit of doing so is
> the requirement for supporting PCI on Hyper-V for ARM64, because the
> host bridge of Hyper-V doesn't have pci_config_window, whereas ARM64 is
> a PCI_DOMAINS_GENERIC=y arch, so we cannot retrieve the PCI domain
> number from pci_config_window on ARM64 Hyper-V guest.
> 
> As the preparation for ARM64 Hyper-V PCI support, we introduce the
> domain_nr in pci_host_bridge and a sentinel value to allow drivers to
> set domain numbers properly at probing time. Currently
> CONFIG_PCI_DOMAINS_GENERIC=y archs are only users of this
> newly-introduced field.
> 
> Signed-off-by: Boqun Feng <boqun.feng@...il.com>

Once all the issues are ironed out, Lorenzo should probably merge this
since it's primarily Hyper-V stuff, but I'm OK with this part:

Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>

But fix the comment issue below.

> ---
>  drivers/pci/probe.c |  6 +++++-
>  include/linux/pci.h | 10 ++++++++++
>  2 files changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 79177ac37880..60c50d4f156f 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -594,6 +594,7 @@ static void pci_init_host_bridge(struct pci_host_bridge *bridge)
>  	bridge->native_pme = 1;
>  	bridge->native_ltr = 1;
>  	bridge->native_dpc = 1;
> +	bridge->domain_nr = PCI_DOMAIN_NR_NOT_SET;
>  
>  	device_initialize(&bridge->dev);
>  }
> @@ -898,7 +899,10 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
>  	bus->ops = bridge->ops;
>  	bus->number = bus->busn_res.start = bridge->busnr;
>  #ifdef CONFIG_PCI_DOMAINS_GENERIC
> -	bus->domain_nr = pci_bus_find_domain_nr(bus, parent);
> +	if (bridge->domain_nr == PCI_DOMAIN_NR_NOT_SET)
> +		bus->domain_nr = pci_bus_find_domain_nr(bus, parent);
> +	else
> +		bus->domain_nr = bridge->domain_nr;
>  #endif
>  
>  	b = pci_find_bus(pci_domain_nr(bus), bridge->busnr);
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 540b377ca8f6..2c413a64d168 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -526,6 +526,15 @@ static inline int pci_channel_offline(struct pci_dev *pdev)
>  	return (pdev->error_state != pci_channel_io_normal);
>  }
>  
> +/*
> +* Currently in ACPI spec, for each PCI host bridge, PCI Segment Group number is
> +* limited to a 16-bit value, therefore (int)-1 is not a valid PCI domain number,
> +* and can be used as a sentinel value indicating >domain_nr is not set by the
> +* driver (and CONFIG_PCI_DOMAINS_GENERIC=y archs will set it with
> +* pci_bus_find_domain_nr()).
> +*/

Fix comment indentation (follow style of other comments in this file).

s/>domain_nr/->domain_nr/

> +#define PCI_DOMAIN_NR_NOT_SET (-1)
> +
>  struct pci_host_bridge {
>  	struct device	dev;
>  	struct pci_bus	*bus;		/* Root bus */
> @@ -533,6 +542,7 @@ struct pci_host_bridge {
>  	struct pci_ops	*child_ops;
>  	void		*sysdata;
>  	int		busnr;
> +	int		domain_nr;
>  	struct list_head windows;	/* resource_entry */
>  	struct list_head dma_ranges;	/* dma ranges resource list */
>  	u8 (*swizzle_irq)(struct pci_dev *, u8 *); /* Platform IRQ swizzler */
> -- 
> 2.30.2
>