About ARM TCM patch
Dear ML,
I read the TCM patch from http://lwn.net/Articles/353032/
It said:
Code executing inside the ITCM does not "see" any MMU mappings and e.g. register accesses must be made to physical addresses.
I am doubt it is correctly for all systems, at my SoC platform(arm1136JF, v6), the situation is difference.
1. After MMU open, the code running at ITCM can't see physical address for register.
2. After MMU open, the code can't run at physical addressed ITCM.
Signature · 2 lines
Best regards, Peter Chen
Hi Peter,
Quoted 8 lines · Peter Chen
Dear ML,
I read the TCM patch from http://lwn.net/Articles/353032/
It said:
Code executing inside the ITCM does not "see" any MMU mappings and e.g. register accesses must be made to physical addresses.
Quoted 7 lines
I am doubt it is correctly for all systems, at my SoC
platform(arm1136JF, v6), the situation is difference.1. After MMU open, the code running at ITCM can't see physical address for register.
2. After MMU open, the code can't run at physical addressed ITCM.
That's my understanding as well. Once the MMU is enabled, ALL access go through the MMU, whether they originate from the ITCM or not.
Signature · 3 lines
Dave Hylands Shuswap, BC, Canada http://www.DaveHylands.com/
2009/9/25 Peter Chen <[email protected]>:
Quoted 1 line
I read the TCM patch from http://lwn.net/Articles/353032/
Are you trying to use it too?
Quoted 4 lines
1. After MMU open, the code running at ITCM can't see physical address for register.
2. After MMU open, the code can't run at physical addressed ITCM.
Could this be different between ARM9 (which I use) and ARM11?
Linus Walleij
2009/9/25 Linus Walleij <[email protected]>:
Quoted 8 lines
2009/9/25 Peter Chen <[email protected]>:
Quoted 4 lines
1. After MMU open, the code running at ITCM can't see physical address for register.
2. After MMU open, the code can't run at physical addressed ITCM.
Could this be different between ARM9 (which I use) and ARM11?
Thinking about it this rings a bell. I know it behaves like described on ARM9, so code executing in TCM can only "see" physical memory.
But one difference between the ARM9 and ARM11 families is that the cache is mapped to virtual (MMU:ed) address space in ARM9 and to physical address space in ARM11 is it not? (Is this so already in ARM10 BTW?)
So just thinking intuitively about it, as a TCM memory is very close to what a cache is to the CPU I think it's something like this on ARM9:
CPU
/ \
Cache TCM
| |
MMU |
| |External memory interface
But on ARM11 (ARM10?):
CPU
|
MMU
/ \Cache TCM
|
External memory interface
Is that correct more or less? Catalin would you happen to know this?
Anyway the code should still work actually, since we make a 1-1 memory map anyway. But you cannot place the TCM in the memory locations I chose for U300 since these are occupied on ARM11.
Linus Walleij
Quoted 34 lines · Linus Walleij
2009/9/25 Linus Walleij <[email protected]>:
Quoted 8 lines
2009/9/25 Peter Chen <[email protected]>:
Quoted 4 lines
1. After MMU open, the code running at ITCM can't see physical address for register.
2. After MMU open, the code can't run at physical addressed ITCM.
Could this be different between ARM9 (which I use) and ARM11?
Thinking about it this rings a bell. I know it behaves like described on ARM9, so code executing in TCM can only "see" physical memory.
But one difference between the ARM9 and ARM11 families is that the cache is mapped to virtual (MMU:ed) address space in ARM9 and to physical address space in ARM11 is it not? (Is this so already in ARM10 BTW?)
So just thinking intuitively about it, as a TCM memory is very close to what a cache is to the CPU I think it's something like this on ARM9:
CPU / \ Cache TCM | | MMU | | |External memory interface
But on ARM11 (ARM10?):
CPU | MMU / \
Quoted 5 lines
Cache TCM
|
External memory interfaceIs that correct more or less? Catalin would you happen to know this?
I think you are right.
Quoted 3 lines
Anyway the code should still work actually, since we make a 1-1 memory map anyway. But you cannot place the TCM in the memory locations I chose for U300 since these are occupied on ARM11.
Sorry, I haven't tried your patch at kernel, I just did experiments at u-boot.
Quoted 1 line
Linus Walleij
Signature · 2 lines
Best Regards Peter Chen