From: Marcelo Tosatti <marcelo.tosatti@cyclades•com>
To: Dan Malek <dan@embeddededge•com>
Cc: linux-ppc-embedded <linuxppc-embedded@ozlabs•org>
Subject: Re: [PATCH] 8xx: fix usage of pinned 8Mbyte TLB entries
Date: Fri, 6 May 2005 10:38:58 -0300 [thread overview]
Message-ID: <20050506133858.GA6032@logos.cnet> (raw)
In-Reply-To: <1b2c7da800815bcdd76ddf27a2ab9c55@embeddededge.com>
> >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?
> >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.
>
> >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.
>
> >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.
>
> >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.
next prev parent reply other threads:[~2005-05-06 18:10 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-05-05 17:20 [PATCH] 8xx: fix usage of pinned 8Mbyte TLB entries Marcelo Tosatti
2005-05-06 13:04 ` Jason McMullan
2005-05-06 11:39 ` Marcelo Tosatti
2005-05-06 16:43 ` Dan Malek
2005-05-06 13:38 ` Marcelo Tosatti [this message]
2005-05-06 22:49 ` Dan Malek
2005-05-06 20:03 ` Marcelo Tosatti
2005-05-07 3:09 ` Dan Malek
2005-05-06 23:05 ` Marcelo Tosatti
2005-05-07 4:39 ` Dan Malek
2005-05-07 5:16 ` Dan Malek
2005-05-07 13:16 ` Marcelo Tosatti
2005-05-07 20:02 ` Dan Malek
2005-05-07 15:47 ` Marcelo Tosatti
2005-05-07 14:05 ` Marcelo Tosatti
2005-05-09 6:09 ` Pantelis Antoniou
2005-05-07 14:59 ` Wolfgang Denk
2005-05-07 5:27 ` Dan Malek
2005-05-07 5:55 ` Dan Malek
2005-05-06 23:10 ` Dan Malek
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