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

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Date:	Wed, 14 May 2014 20:34:10 +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 Wednesday 14 May 2014 06:15 PM, Arnd Bergmann wrote:
> On Wednesday 14 May 2014 11:14:45 Kishon Vijay Abraham I wrote:
>> hi Arnd,
>>
>> On Tuesday 13 May 2014 07:04 PM, Arnd Bergmann wrote:
>>> On Tuesday 13 May 2014 15:27:46 Arnd Bergmann wrote:
>>>> On Tuesday 13 May 2014 18:56:23 Kishon Vijay Abraham I wrote:
>>>>>> 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).
>>>>>
>>>>
>>>> Then use the first of the two?
>>>>
>>>
>>> To clarify: using <0x82000000 0 0  0xb0000000  0 0x10000000> will give you 
>>> a mem_offset of 0xb0000000, which should work just fine for this case.
>>>
>>> What I don't understand is why the ATU cares about whether the outbound
>>> address is 0x0000000 or 0xb0000000 if it just decodes the lower 28 bit
>>> anyway. Did you mean that we have to program the BARs using low addresses
>>> regardless of what is programmed in the ATU? That would make more sense,
>>> and it also matches what I suggested.
>>
>> No, It's not like it decodes only the lower 28bits. The BARs is programmed with
>> 32 bit value.
>>
>> My pcie dt node has
>>  ranges = <0x00000800 0 0x20001000 0x20001000 0 0x00002000  /* CONFIG */
>>            0x81000000 0 0          0x20003000 0 0x00010000  /* IO */
>>            0x82000000 0 0x20013000 0x20013000 0 0xffed000>; /* MEM */
>>
>> Consider MEM address space..
>>
>> Here both PCI address and CPU address is 0x20013000. So when there is a write
>> to cpu addr 0x20013000 [writel(virt_addr(0x20013000)], we want it to be
>> translated to PCI addr 0x20013000. So in 'ATU', we would expect *base* to be
>> programmed to *0x20013000* and target to be programmed to *0x20013000*. But
>> that's not the case for DRA7xx. For DRA7xx *base* should be programmed to
>> *0x0013000* and target should be programmed to *0x20013000*.
> 
> Ok, got it, thanks for your patience.
> 
> I think this would best be modeled as a separate bus node that contains the
> restriction, like this:
> 
> / {
> 	#address-cells = <1>; // or <2> if you support > 4GB address space
> 	#size-cells = <1>;
> 
> 	soc {
> 		#address-cells <1>;
> 		#size-cells = <1>;
> 		ranges;
> 		dma-ranges;
> 
> 		... // all normal devices
> 
> 		axi@...00000 {
> 			#size-cells = <1>;
> 			#address-cells = <1>;
> 			dma-ranges; // can access all 4GB outbound
> 			ranges = <0 0x20000000 0x10000000>; // 28-bit bus
> 
> 			pci@0 {
> 				reg = <0x0    0x1000>, // internal regs
> 				      <0x1000 0x2000>; // config space
> 				dma-ranges; // 32-bit outbound
> 				ranges = <0x81000000 0 0           0x3000 0 0x00010000  /* IO */
> 					  0x82000000 0 0x20013000 0x13000 0 0xffed000>; /* MEM */
> 			};
> 		};
> 	};
> };

Nice :-)

Thanks
Kishon
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