On 03/23/2012 06:44 AM, Prabhakar Kushwaha wrote:
Hi Scott,
On Friday 23 March 2012 01:13 AM, Scott Wood wrote:
On 03/22/2012 12:52 AM, Prabhakar Kushwaha wrote:
Hi Scott,
Please find my reply in-lined
On Thursday 22 March 2012 01:22 AM, Scott Wood wrote:
On 03/20/2012 11:43 PM, Prabhakar Kushwaha wrote:
Debugging of e500 and e500v1 processer requires debug exception vecter (IVPR + IVOR15) to have valid and fetchable OP code.
While executing in translated space (AS=1), whenever a debug exception is generated, the MSR[DS/IS] gets cleared i.e. AS=0 and the processor tries to fetch an instruction from the debug exception vector (IVPR + IVOR15); since now we are in AS=0, the application needs to ensure the proper TLB configuration to have (IVOR + IVOR15) accessible from AS=0 also.
Create a temporary TLB in AS0 to make sure debug exception verctor is accessible on debug exception.
Signed-off-by: Radu Lazarescuradu.lazarescu@freescale.com Signed-off-by: Marius Grigorasmarius.grigoras@freescale.com Signed-off-by: Prabhakar Kushwahaprabhakar@freescale.com
Can you document the flow of exactly what TLB entries are present at various points of the boot flow, for all the various configurations (NOR boot, NAND SPL, RAMBOOT, IFC versus non-IFC, etc).
Sure. May be separate patch will be send.
Let's start with just an e-mail thoroughly describing your understanding of this. It will provide necessary context for review.
We can clean it up for permanent documentation once it's clear to everyone what's going on.
Sure. I will start this activity from now. But i will suggest not to combine both patches. let debugger patch to go ahead , if required i will send required patch later-on.
My point is that I cannot fully follow what's going on here without spending a bunch of time looking at it, and I don't see anyone else stepping up to review this, so I'd like to see a write-up of what's going on so that I can properly review these patches.
In the ramboot case is this really supposed to be I+G?
I am not sure. But same is done under label "create_init_ram_area" for TLB entry 15. what you suggest.
I suggest as part of the request to document all of this, you figure out what should actually be mapped in each configuration. The existing code might be wrong for some of them, but we shouldn't proceed ahead blindly and make an even bigger mess.
After internal discussion we can have following settings for non-RAMBOOT(NOR boot) ==> I + G for RAMBOOT ==> I, cache inhibited is required as L1 cache is used as stack.
Why does using L1 for a stack mean that the mapping must be cache inhibited? Why do we even need to use L1 for a stack with ramboot?
I=0 it means the memory range is cacheable, so an access to an address from that range could get the line in cache. If you are using the cache as a memory zone(L1 as stack), it may overwrite some data in cache and replace it with the last access.
It will not do that -- when we use L1 (or part of it) for an early stack, we lock the cache lines.
Which path will NAND SPL go through (not the payload, but the SPL itself)? That will be only a 4K window mapped, and guarded doesn't stop speculative instruction fetches, so we don't want to map more than is backed up by something.
NAND SPL go via !defined(CONFIG_SYS_RAMBOOT) path.
i think NAND_SPL does not require temporary TLB as NAND SPL even does not have any interrupt vector.
So there's no plan to support using breakpoints or single step during the SPL? That's fine with me, but should be documented, and we should make sure this code does not run in that case.
Breakpoints will work as it is. No impact will be on debugging for NAND SPL.
Generally any debugger use some initial configuration file. Only problem occurs when application modifies those configuration.
Then why do we need to set MSR[DE] on entry, if the debugger can take care of it?
- lis r10,0xffc00000@h
- ori r10,r10,0xffc00000@l
Don't waste instructions -- this could be in an SPL. That ori is a no-op.
Please refer above response. May be this piece of code is not required for NAND SPL
Still, I'd like to know why you're writing 0xffc00000 to MAS7. Only the low 4 bits of MAS7 are valid on current e500.
The reason for using 0xffc00000 to support e6500 - since it supports 40-bit physical addresses, the last 8 bits of MAS7 are defined.
Regardless, you're setting the wrong end of MAS7. It's the *lower* bits, not the upper bits, that are used.
And we should not be doing anything special for e6500 here. e6500 does not need this, and e6500 platforms should not set CONFIG_SYS_PPC_E500_DEBUG_TLB.
But i am not sure whether e6500 will be part of mpc85xx or not.
It will.
So, I will use as #ifdef CONFIG_ENABLE_36BIT_PHYS lis r10,0x0000 #endif
Why?
-Scott