xref: /openbmc/linux/arch/x86/kernel/cpu/mtrr/amd.c (revision 2ec1df41)

#include <linux/init.h>
#include <linux/mm.h>
#include <asm/mtrr.h>
#include <asm/msr.h>

#include "mtrr.h"

static void
amd_get_mtrr(unsigned int reg, unsigned long *base,
	     unsigned long *size, mtrr_type * type)
{
	unsigned long low, high;

	rdmsr(MSR_K6_UWCCR, low, high);
	/*  Upper dword is region 1, lower is region 0  */
	if (reg == 1)
		low = high;
	/*  The base masks off on the right alignment  */
	*base = (low & 0xFFFE0000) >> PAGE_SHIFT;
	*type = 0;
	if (low & 1)
		*type = MTRR_TYPE_UNCACHABLE;
	if (low & 2)
		*type = MTRR_TYPE_WRCOMB;
	if (!(low & 3)) {
		*size = 0;
		return;
	}
	/*
	 *  This needs a little explaining. The size is stored as an
	 *  inverted mask of bits of 128K granularity 15 bits long offset
	 *  2 bits
	 *
	 *  So to get a size we do invert the mask and add 1 to the lowest
	 *  mask bit (4 as its 2 bits in). This gives us a size we then shift
	 *  to turn into 128K blocks
	 *
	 *  eg              111 1111 1111 1100      is 512K
	 *
	 *  invert          000 0000 0000 0011
	 *  +1              000 0000 0000 0100
	 *  *128K   ...
	 */
	low = (~low) & 0x1FFFC;
	*size = (low + 4) << (15 - PAGE_SHIFT);
	return;
}

static void amd_set_mtrr(unsigned int reg, unsigned long base,
			 unsigned long size, mtrr_type type)
/*  [SUMMARY] Set variable MTRR register on the local CPU.
    <reg> The register to set.
    <base> The base address of the region.
    <size> The size of the region. If this is 0 the region is disabled.
    <type> The type of the region.
    <do_safe> If TRUE, do the change safely. If FALSE, safety measures should
    be done externally.
    [RETURNS] Nothing.
*/
{
	u32 regs[2];

	/*
	 *  Low is MTRR0 , High MTRR 1
	 */
	rdmsr(MSR_K6_UWCCR, regs[0], regs[1]);
	/*
	 *  Blank to disable
	 */
	if (size == 0)
		regs[reg] = 0;
	else
		/* Set the register to the base, the type (off by one) and an
		   inverted bitmask of the size The size is the only odd
		   bit. We are fed say 512K We invert this and we get 111 1111
		   1111 1011 but if you subtract one and invert you get the
		   desired 111 1111 1111 1100 mask

		   But ~(x - 1) == ~x + 1 == -x. Two's complement rocks!  */
		regs[reg] = (-size >> (15 - PAGE_SHIFT) & 0x0001FFFC)
		    | (base << PAGE_SHIFT) | (type + 1);

	/*
	 *  The writeback rule is quite specific. See the manual. Its
	 *  disable local interrupts, write back the cache, set the mtrr
	 */
	wbinvd();
	wrmsr(MSR_K6_UWCCR, regs[0], regs[1]);
}

static int amd_validate_add_page(unsigned long base, unsigned long size, unsigned int type)
{
	/* Apply the K6 block alignment and size rules
	   In order
	   o Uncached or gathering only
	   o 128K or bigger block
	   o Power of 2 block
	   o base suitably aligned to the power
	*/
	if (type > MTRR_TYPE_WRCOMB || size < (1 << (17 - PAGE_SHIFT))
	    || (size & ~(size - 1)) - size || (base & (size - 1)))
		return -EINVAL;
	return 0;
}

static struct mtrr_ops amd_mtrr_ops = {
	.vendor            = X86_VENDOR_AMD,
	.set               = amd_set_mtrr,
	.get               = amd_get_mtrr,
	.get_free_region   = generic_get_free_region,
	.validate_add_page = amd_validate_add_page,
	.have_wrcomb       = positive_have_wrcomb,
};

int __init amd_init_mtrr(void)
{
	set_mtrr_ops(&amd_mtrr_ops);
	return 0;
}

//arch_initcall(amd_mtrr_init);