> --- Ursprüngliche Nachricht --- > Von: Benjamin Herrenschmidt <[EMAIL PROTECTED]> > An: Gerhard Pircher <[EMAIL PROTECTED]> > Kopie: [EMAIL PROTECTED], [email protected] > Betreff: Re: Unmapping pages from the linear addressing without > HIGHMEM support > Datum: Fri, 10 Mar 2006 09:11:41 +1100 > > On Thu, 2006-03-09 at 14:51 +0100, Gerhard Pircher wrote: > > Hi, > > > > I'm trying to implement non-coherent DMA for PPC desktop systems (like > > the AmigaOne with G3/G4 CPU). For this I want to use the code in > > arch/ppc/kernel/dma-mapping.c. The DMA memory allocation function > > implemented in this file allocates pages with alloc_pages() and maps > > them to its own linear address space, but without unmapping the > > allocated pages from the kernel linear addressing. Due to this the > > pages are mapped twice, which results in a conflict between the > > different WIMG settings of the pages. > > > > Is there an API that can be used to unmap the allocated pages from the > > kernel linear addressing? I thought about using kunmap() and > > flush_all_zero_pkmaps(), but I'm not sure if this is the right approach > > and HIGHMEM doesn't work on the AmigaOne too (the highmem base is > > occupied by the PCI/ISA I/O space!). Wouldn't it be possible to just > > clear the valid (V) bit of the PTE and do a TLB cache flush? > > The main problem is that the mappings may be covered by a BAT and thus > pages may not be unmappable individually... > > What I would suggest is that your dig in the low level RAM mapping code > and limit it at boot to RAM minus a pool of the size you want. That would mean I cannot reuse the code in dma-mapping.c, right? Killing the BAT mappings or limiting the memory size covered by the BATs seems to be fairly easy, but I guess I have to setup my own page table for the reserved DMA memory area and implement my own alloc_pages() function!?
Thanks! Gerhard -- Echte DSL-Flatrate dauerhaft für 0,- Euro*! "Feel free" mit GMX DSL! http://www.gmx.net/de/go/dsl -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
