[U-Boot] PCIE_MEM_BUS for Freescale SoC

[York Sun <yorksun@freescale.com>]

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.

York