linux-kernel - Re: [PATCH V6 08/13] PCI: generic, thunder: update to use generic ECAM API

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Date:	Fri, 22 Apr 2016 10:30:31 -0400
From:	Jon Masters <jcm@...hat.com>
To:	Tomasz Nowicki <tn@...ihalf.com>, Arnd Bergmann <arnd@...db.de>
Cc:	Jayachandran C <jchandra@...adcom.com>,
	linux-arm-kernel@...ts.infradead.org,
	Bjorn Helgaas <helgaas@...nel.org>,
	Will Deacon <will.deacon@....com>,
	Catalin Marinas <catalin.marinas@....com>, rafael@...nel.org,
	Hanjun Guo <hanjun.guo@...aro.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Sinan Kaya <okaya@...eaurora.org>, jiang.liu@...ux.intel.com,
	linaro-acpi@...ts.linaro.org, linux-pci@...r.kernel.org,
	Liviu.Dudau@....com, David Daney <ddaney@...iumnetworks.com>,
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
	robert.richter@...iumnetworks.com, Suravee.Suthikulpanit@....com,
	msalter@...hat.com, Wangyijing <wangyijing@...wei.com>,
	Marcin Wojtas <mw@...ihalf.com>
Subject: Re: [PATCH V6 08/13] PCI: generic, thunder: update to use generic
 ECAM API

On 04/21/2016 06:08 AM, Tomasz Nowicki wrote:
> On 21.04.2016 11:36, Arnd Bergmann wrote:
>> On Thursday 21 April 2016 11:28:15 Tomasz Nowicki wrote:
>>> On 19.04.2016 15:06, Arnd Bergmann wrote:
>>>> On Monday 18 April 2016 21:31:54 Tomasz Nowicki wrote:
>>>>>
>>>>> Basically the whole content of pci-thunder-ecam.c and
>>>>> pci-thunder-pem.c.
>>>>>
>>>>> pci-thunder-ecam.c contains config space accessors. Similar for
>>>>> pci-thunder-pem.c but it also has extra init call (it is now called
>>>>> thunder_pem_init) which finds and maps related registers.
>>>>
>>>> They seem to do much more than just override the accessors, they
>>>> actually
>>>> change the contents of the config space as well. Is that really
>>>> necessary
>>>> on ACPI based systems as well?
>>>
>>> Yes, the pci-thunder-ecam.c accessors are meant to emulate config space
>>> capabilities. They are necessary to synthesize EA capabilities (fixed
>>> PCI BARs), it wont work without this, for ACPI boot as well.
>>
>> Why is that? I thought the BARs never get reassigned when using ACPI,
>> so I'm surprised it's actually needed. Maybe I misunderstood what
>> you mean by fixed PCI BARs.
> 
> Yes, I meant something else. ThunderX has non-programmable PCI BAR
> addresses. So it uses PCI EA (Extended allocation) capabilities to get
> know PCI BARs addresses. But the early implementation (pass1.x) misses
> EA capabilities hence we need to emulate it in config space accessors.

Aside: In case it's helpful, at least one enterprise vendor I know of is
only supporting later silicon as a result of this. So IMO there's no
need to worry about this issue on the early preproduction chips.

-- 
Computer Architect | Sent from my Fedora powered laptop