Seems like no one picked up the ball to run with this, so I made the
trivial changes needed to make the PixelStamp driver be able to get its
DMA memory without an awful hack.

To reiterate what this patch does:  It places the first 8M of RAM onto a
separate, lower-priority free list, which will only be used by the VM
system if the default free list (which has memory > 8M) is exhausted.

This means that the PixelStamp driver should be able to allocate memory
within its constraints without magically reserving the amount of space
needed + slop in machdep.c.  (bus_dmamem_alloc() is what you want for
allocating the memory in the `px' driver.)

I haven't tested it yet, but it's basically what the i386 port does for
ISA DMA'able memory.

This patch should be committed before the 1.4 branch is made.

        -- Jason R. Thorpe <thorpej@nas.nasa.gov>

Index: include/vmparam.h
===================================================================
RCS file: /cvsroot/src/sys/arch/pmax/include/vmparam.h,v
retrieving revision 1.8
diff -c -r1.8 vmparam.h
*** vmparam.h	1998/07/08 04:43:19	1.8
--- vmparam.h	1999/03/31 00:12:23
***************
*** 5,14 ****
  /*
   * DECstation has one physical memory segment.
   */
! #define	VM_PHYSSEG_MAX		1
  
! #define	VM_NFREELIST		1
  #define	VM_FREELIST_DEFAULT	0
  
  /* pcb base */
  /*#define	pcbb(p)		((u_int)(p)->p_addr) */
--- 5,17 ----
  /*
   * DECstation has one physical memory segment.
   */
! #define	VM_PHYSSEG_MAX		2	/* 2 free lists */
! #define	VM_PHYSSEG_STRAT	VM_PSTRAT_BSEARCH
! #define	VM_PHYSSEG_NOADD		/* can't add RAM after vm_mem_init */
  
! #define	VM_NFREELIST		2
  #define	VM_FREELIST_DEFAULT	0
+ #define	VM_FREELIST_FIRST8	1
  
  /* pcb base */
  /*#define	pcbb(p)		((u_int)(p)->p_addr) */
Index: pmax/machdep.c
===================================================================
RCS file: /cvsroot/src/sys/arch/pmax/pmax/machdep.c,v
retrieving revision 1.133
diff -c -r1.133 machdep.c
*** machdep.c	1999/03/28 01:56:41	1.133
--- machdep.c	1999/03/31 00:12:23
***************
*** 482,492 ****
  
  	/*
  	 * Load the rest of the available pages into the VM system.
  	 */
  	first = round_page(MIPS_KSEG0_TO_PHYS(kernend));
  	last = mem_clusters[0].start + mem_clusters[0].size;
! 	uvm_page_physload(atop(first), atop(last), atop(first), atop(last),
! 	    VM_FREELIST_DEFAULT);
  
  	/*
  	 * Initialize error message buffer (at end of core).
--- 482,503 ----
  
  	/*
  	 * Load the rest of the available pages into the VM system.
+ 	 * Put the first 8M of RAM onto a lower-priority free list, since
+ 	 * some TC boards (e.g. PixelStamp boards) are only able to DMA
+ 	 * into this region, and we want them to have a fighting chance of
+ 	 * allocating their DMA memory during autoconfiguratoin.
  	 */
  	first = round_page(MIPS_KSEG0_TO_PHYS(kernend));
  	last = mem_clusters[0].start + mem_clusters[0].size;
! 	if (last <= (8 * 1024 * 1024)) {
! 		uvm_page_physload(atop(first), atop(last), atop(first),
! 		    atop(last), VM_FREELIST_DEFAULT);
! 	} else {
! 		uvm_page_physload(atop(first), atop(8 * 1024 * 1024),
! 		    atop(first), atop(8 * 1024 * 1024), VM_FREELIST_FIRST8);
! 		uvm_page_physload(atop(8 * 1024 * 1024), atop(last),
! 		    atop(8 * 1024 * 1024), atop(last), VM_FREELIST_DEFAULT);
! 	}
  
  	/*
  	 * Initialize error message buffer (at end of core).