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 21:43:58 +0530
From:	Jayachandran C <jchandra@...adcom.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Tomasz Nowicki <tn@...ihalf.com>,
	Bjorn Helgaas <helgaas@...nel.org>,
	Will Deacon <will.deacon@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Rafael Wysocki <rafael@...nel.org>,
	Hanjun Guo <hanjun.guo@...aro.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Sinan Kaya <okaya@...eaurora.org>,
	robert.richter@...iumnetworks.com, Marcin Wojtas <mw@...ihalf.com>,
	Liviu.Dudau@....com, David Daney <ddaney@...iumnetworks.com>,
	Wangyijing <wangyijing@...wei.com>,
	Suravee Suthikulanit <Suravee.Suthikulpanit@....com>,
	Mark Salter <msalter@...hat.com>,
	Linux PCI <linux-pci@...r.kernel.org>,
	linux-arm-kernel@...ts.infradead.org,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linaro-acpi@...ts.linaro.org, Jon Masters <jcm@...hat.com>,
	Andrea Gallo <andrea.gallo@...aro.org>,
	Duc Dang <dhdang@....com>, jeremy.linton@....com,
	liudongdong3@...wei.com, Christopher Covington <cov@...eaurora.org>
Subject: Re: [PATCH V8 9/9] pci, acpi: ARM64 support for ACPI based generic
 PCI host controller

On Mon, May 30, 2016 at 9:08 PM, Arnd Bergmann <arnd@...db.de> wrote:
> 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.

The map_bus provided by pci-ecam.h is already trivial in 64bit case,
it was written so that it could be optimized at compile time. The
pci_ecam_create is a useful to have here instead of redoing the
request_resource/ioremap sequence.

The struct pci_config_window can be moved into struct
pci_host_bridge (or a wrapper of pci_host_bridge) when we have
the setup to point bus->sysdata to something like that. The ECAM
API can be fixed up to handle that case as well. I did not make
any changes since the pci_host_bridge discussion is still going on.

JC.