linux-kernel - Re: [PATCH V8 9/9] pci, acpi: ARM64 support for ACPI based generic PCI host controller

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Date:	Mon, 30 May 2016 17:38:13 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Tomasz Nowicki <tn@...ihalf.com>
Cc:	helgaas@...nel.org, will.deacon@....com, catalin.marinas@....com,
	rafael@...nel.org, hanjun.guo@...aro.org,
	Lorenzo.Pieralisi@....com, okaya@...eaurora.org,
	jchandra@...adcom.com, robert.richter@...iumnetworks.com,
	mw@...ihalf.com, Liviu.Dudau@....com, ddaney@...iumnetworks.com,
	wangyijing@...wei.com, Suravee.Suthikulpanit@....com,
	msalter@...hat.com, linux-pci@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org, linaro-acpi@...ts.linaro.org,
	jcm@...hat.com, andrea.gallo@...aro.org, dhdang@....com,
	jeremy.linton@....com, liudongdong3@...wei.com, cov@...eaurora.org
Subject: Re: [PATCH V8 9/9] pci, acpi: ARM64 support for ACPI based generic PCI host controller

On Monday, May 30, 2016 5:14:22 PM CEST Tomasz Nowicki wrote:
> +       bsz = 1 << pci_generic_ecam_ops.bus_shift;
> +       cfgres.start = root->mcfg_addr + bus_res->start * bsz;
> +       cfgres.end = cfgres.start + resource_size(bus_res) * bsz - 1;
> +       cfgres.flags = IORESOURCE_MEM;
> +       cfg = pci_ecam_create(&root->device->dev, &cfgres, bus_res,
> +                             &pci_generic_ecam_ops);
> +       if (IS_ERR(cfg)) {
> +               pr_err("%04x:%pR error %ld mapping CAM\n", seg, bus_res,
> +                      PTR_ERR(cfg));
> +               return PTR_ERR(cfg);
> +       }
> +
> +       ri->cfg = cfg;
> +       return 0;
> +}

I wonder if we could do this a little simpler and just put a pointer
to the mmconfig space into struct pci_host_bridge, and then have a trivial
map_bus function alongside pci_generic_config_read/pci_generic_config_write.

As this code is specific to arch/arm64, we don't need any of the complexity
of drivers/pci/ecam.c, which basically only exists to work around the
limited virtual address space of 32-bit machines.

	Arnd