linux-kernel - Re: [PATCH 06/17] pci: host: pcie-designware: Use *base-mask* for configuring the iATU

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Date:	Tue, 13 May 2014 18:56:23 +0530
From:	Kishon Vijay Abraham I <kishon@...com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	Jingoo Han <jg1.han@...sung.com>,
	"'Santosh Shilimkar'" <santosh.shilimkar@...com>,
	<devicetree@...r.kernel.org>, <linux-doc@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-omap@...r.kernel.org>, <linux-pci@...r.kernel.org>,
	<rogerq@...com>, <balajitk@...com>,
	"'Bjorn Helgaas'" <bhelgaas@...gle.com>,
	"'Marek Vasut'" <marex@...x.de>
Subject: Re: [PATCH 06/17] pci: host: pcie-designware: Use *base-mask* for
 configuring the iATU

Hi Arnd,

On Tuesday 13 May 2014 06:17 PM, Arnd Bergmann wrote:
> On Tuesday 13 May 2014 18:01:59 Kishon Vijay Abraham I wrote:
>> On Thursday 08 May 2014 02:48 PM, Arnd Bergmann wrote:
>>> On Thursday 08 May 2014 18:05:11 Jingoo Han wrote:
>>>> On Tuesday, May 06, 2014 10:59 PM, Arnd Bergmann wrote:
>>>>> On Tuesday 06 May 2014 19:03:52 Kishon Vijay Abraham I wrote:
>>>>>> In DRA7, the cpu sees 32bit address, but the pcie controller can see only 28bit
>>>>>> address. So whenever the cpu issues a read/write request, the 4 most
>>>>>> significant bits are used by L3 to determine the target controller.
>>>>>> For example, the cpu reserves 0x2000_0000 - 0x2FFF_FFFF for PCIe controller but
>>>>>> the PCIe controller will see only (0x000_0000 - 0xFFF_FFF). So for programming
>>>>>> the outbound translation window the *base* should be programmed as 0x000_0000.
>>>>>> Whenever we try to write to say 0x2000_0000, it will be translated to whatever
>>>>>> we have programmed in the translation window with base as 0x000_0000.
>>>>>>
>>>>>> Cc: Bjorn Helgaas <bhelgaas@...gle.com>
>>>>>> Cc: Marek Vasut <marex@...x.de>
>>>>>> Signed-off-by: Kishon Vijay Abraham I <kishon@...com>
>>>>>> Acked-by: Jingoo Han <jg1.han@...sung.com>
>>>>>> Acked-by: Mohit Kumar <mohit.kumar@...com>
>>>>>
>>>>> Sorry, but NAK.
>>>>>
>>>>> We have a standard 'dma-ranges' property to handle this, so use it.
>>>>>
>>>>> See the x-gene PCIe driver patches for an example. Please also talk
>>>>> to Santosh about it, as he is implementing generic support for
>>>>> parsing dma-ranges in platform devices at the moment.
>>>>
>>>> Hi Arnd,
>>>>
>>>> Do you mean the following patch?
>>>> http://www.spinics.net/lists/kernel/msg1737725.html
>>>>
>>>
>>> That is the patch Santosh did for platform devices, which is related but not
>>> what I meant here. For the PCI inbound window setup, please have a look
>>> at https://lkml.org/lkml/2014/3/19/607
>>
>> Do you think it can be used for *outbound* window setup too? The problem is the
>> *ranges* property defines both the pci address and cpu address which should
>> have been enough to program the ob translation window, but the hw is designed
>> so that the controller sees only the 28 bits. (The most significant 4 bits is
>> for the l3 to address the controller).
> 
> I'm not following what the problem is. You should always be able to describe
> in the inbound window (that is from the CPU perspective) using dma-ranges
> and the outbound window using ranges.
> 
> If you have a case where the outbound translation is a 256MB (i.e. 28bit)
> section of the CPU address space, that could be represented as
> 
> 	ranges = <0x82000000 0 0  0xb0000000  0 0x10000000>;
> 
> or 
> 
> 	ranges = <0x82000000 0 0xb0000000  0xb0000000  0 0x10000000>;
> 
> depending on whether you want the BARs to be programmed using a low
> address 0x0-0x0fffffff or an address matching the window
> 0xb0000000-0xbfffffff.

The problem is, for configuring the window starting at 0xb0000000, the ATU
should be programmed 0x0000000 (the cpu address for it will be 0xb0000000 though).

Thanks
Kishon
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