[U-Boot] PCIE_MEM_BUS for Freescale SoC

[Scott Wood]

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.

-Scott