Re: [PATCH] 8xx: fix usage of pinned 8Mbyte TLB entries

quoted

The following patch changes "mmu_mapin_ram" (hook used by mapin_ram), 
to
begin creation of pagetables after the first 8Megs, preserving the
8Mbyte TLB entry.

Please don't do this.  It isn't necessary.

Why it is not necessary? 

Have you read the section of the manual which I pasted here? 

quoted

This changes the assumption that DMA allocations can start at the first
kernel address, given that those need to be marked uncached due to DMA
cache coherency issues.

VM space for uncached DMA has always been allocated using vmalloc(),
the location of the physical pages backing this space is irrelevant.    

The only thing you have to ensure is the virtual address is outside 
of the pinned entry.  

What you replied to is:

"This changes the assumption that DMA allocations can start at the first
kernel address, given that those need to be marked uncached due to DMA
cache coherency issues." 

I think we mean the same, yes? 

If something about the way the VM space is structured in 2.6 is
different, we need to fix that in general. 

quoted

Panto: FEC currently does

       mem_addr = __get_free_page(GFP_KERNEL);
       cbd_base = (cbd_t *)mem_addr;

This is just plain broken and it shouldn't do this.

quoted

We are still using v2.4 FEC driver, so this fixed it:

//      mem_addr = __get_free_page(GFP_KERNEL);
       mem_addr = dma_alloc_coherent(NULL, PAGE_SIZE, &physaddr,
                       GFP_KERNEL);

This is the proper way, and should be moved to the equivalent in 2.6.

quoted

Allocateing from the coherent memory DMA region. Which sits at, I 
suppose,
after initial 8Megs in all configurations (should be always).

You are making this too complicated :-)  All we have to do is use the
proper dma allocators and make sure the TLBs are pinned properly.
That is all.

Sorry, but, what is too complicated? 

The patch I sent does two things (pretty much the same thing you suggest 
after stating that its "too complicated", AFAICS):

1) avoids the creation of pte tables in the 8Mbyte range, thus preserving
the pinned TLB entry.
2) restricts bootmem to above 8Mbyte region

And last thing is: 

3) Memory for DMA pages must not be in the pinned region. ie. drivers 
should not allocate memory directly for DMA purposes.

Dan, I would really enjoy having access to some of your precious 8xx
knowledge: share it, along with the correct way to fix this and the 
other pending issues.