[U-Boot] PCIE_MEM_BUS for Freescale SoC

[York Sun]

On 11/23/2015 08:24 AM, Scott Wood wrote:
> On Sat, 2015-11-21 at 15:29 -0800, York Sun wrote:
>>
>> On 11/21/2015 02:55 PM, York Sun wrote:
>>> Roy,
>>>
>>> Do you remember the reason why we use different virtual memory address
>>> from pci
>>> bus address with 36-bit? For example
>>>
>>> include/configs/P1022DS.h-496-#define CONFIG_SYS_PCIE1_MEM_VIRT 0xc0000000
>>> include/configs/P1022DS.h-497-#ifdef CONFIG_PHYS_64BIT
>>> include/configs/P1022DS.h:498:#define CONFIG_SYS_PCIE1_MEM_BUS  0xe0000000
>>> include/configs/P1022DS.h-499-#define CONFIG_SYS_PCIE1_MEM_PHYS
>>> 0xc40000000ull
>>> include/configs/P1022DS.h-500-#else
>>> include/configs/P1022DS.h:501:#define CONFIG_SYS_PCIE1_MEM_BUS  0xc0000000
>>> include/configs/P1022DS.h-502-#define CONFIG_SYS_PCIE1_MEM_PHYS 0xc0000000
>>> include/configs/P1022DS.h-503-#endif
>>>
>>> As far as I can tell, the following is the mapping
>>>
>>> TLB: MEM_VIRT=>MEM_PHYS
>>> PCI: MEM_BUS=>MEM_PHYS
>>> LAW: MEM_PHYS=>pcie interface
>>>
>>> Being different for MEM_VIRT and MEM_BUS cause confusion. When I run "pci
>>> header" command to show the BARs, I expect I can use "md" to access the
>>> BAR
>>> address. That's not the case if MEM_BUS is different from MEM_VIRT.
>>>
>>> I forget why we did this for 36-bit addressing. The MEM_VIRT is the same
>>> as
>>> MEM_BUS for 32-bit addressing. And why do we use the same MEM_BUS address
>>> for
>>> all PCIe hose? I know they are not conflicting, but is it necessary?
>>
>> (I hope Becky and Kumar still follow this mailing list)
>>
>> I dug out an old commit 4c78d4a6c01621721b732418e1c6da684a56bbb1 by Becky
>> Bruce.
>> She believed overlapping the bus address for PCI controllers leaves more
>> space.
>> That's true. But we haven't use more than 512MB in u-boot. If we do need
>> more
>> space, we can easily move things around if we have PHYS_64BIT. If no
>> objection,
>> I'd like to change this back.
> 
> I object.  It's not about how much RAM is used in U-Boot; it's about how much
> memory the OS needs to bounce-buffer for DMA.  The addresses set up by U-Boot
> should match what's in the device tree.  Yes, on 85xx Linux reprograms the
> ATMU based on the device tree rather than trusting U-Boot, but that doesn't
> mean every OS does.

Isn't this backward? I mean the device tree should match u-boot, or u-boot
should fix up the device tree, right?
I checked several device tree files in kernel. We are not using more than 512MB
for each PCI. What's the benefit of using the same address 0xe0000000?

York