1 // SPDX-License-Identifier: GPL-2.0 2 #include <linux/init.h> 3 #include <linux/mm.h> 4 #include <asm/mtrr.h> 5 #include <asm/msr.h> 6 7 #include "mtrr.h" 8 9 static void 10 amd_get_mtrr(unsigned int reg, unsigned long *base, 11 unsigned long *size, mtrr_type *type) 12 { 13 unsigned long low, high; 14 15 rdmsr(MSR_K6_UWCCR, low, high); 16 /* Upper dword is region 1, lower is region 0 */ 17 if (reg == 1) 18 low = high; 19 /* The base masks off on the right alignment */ 20 *base = (low & 0xFFFE0000) >> PAGE_SHIFT; 21 *type = 0; 22 if (low & 1) 23 *type = MTRR_TYPE_UNCACHABLE; 24 if (low & 2) 25 *type = MTRR_TYPE_WRCOMB; 26 if (!(low & 3)) { 27 *size = 0; 28 return; 29 } 30 /* 31 * This needs a little explaining. The size is stored as an 32 * inverted mask of bits of 128K granularity 15 bits long offset 33 * 2 bits. 34 * 35 * So to get a size we do invert the mask and add 1 to the lowest 36 * mask bit (4 as its 2 bits in). This gives us a size we then shift 37 * to turn into 128K blocks. 38 * 39 * eg 111 1111 1111 1100 is 512K 40 * 41 * invert 000 0000 0000 0011 42 * +1 000 0000 0000 0100 43 * *128K ... 44 */ 45 low = (~low) & 0x1FFFC; 46 *size = (low + 4) << (15 - PAGE_SHIFT); 47 } 48 49 /** 50 * amd_set_mtrr - Set variable MTRR register on the local CPU. 51 * 52 * @reg The register to set. 53 * @base The base address of the region. 54 * @size The size of the region. If this is 0 the region is disabled. 55 * @type The type of the region. 56 * 57 * Returns nothing. 58 */ 59 static void 60 amd_set_mtrr(unsigned int reg, unsigned long base, unsigned long size, mtrr_type type) 61 { 62 u32 regs[2]; 63 64 /* 65 * Low is MTRR0, High MTRR 1 66 */ 67 rdmsr(MSR_K6_UWCCR, regs[0], regs[1]); 68 /* 69 * Blank to disable 70 */ 71 if (size == 0) { 72 regs[reg] = 0; 73 } else { 74 /* 75 * Set the register to the base, the type (off by one) and an 76 * inverted bitmask of the size The size is the only odd 77 * bit. We are fed say 512K We invert this and we get 111 1111 78 * 1111 1011 but if you subtract one and invert you get the 79 * desired 111 1111 1111 1100 mask 80 * 81 * But ~(x - 1) == ~x + 1 == -x. Two's complement rocks! 82 */ 83 regs[reg] = (-size >> (15 - PAGE_SHIFT) & 0x0001FFFC) 84 | (base << PAGE_SHIFT) | (type + 1); 85 } 86 87 /* 88 * The writeback rule is quite specific. See the manual. Its 89 * disable local interrupts, write back the cache, set the mtrr 90 */ 91 wbinvd(); 92 wrmsr(MSR_K6_UWCCR, regs[0], regs[1]); 93 } 94 95 static int 96 amd_validate_add_page(unsigned long base, unsigned long size, unsigned int type) 97 { 98 /* 99 * Apply the K6 block alignment and size rules 100 * In order 101 * o Uncached or gathering only 102 * o 128K or bigger block 103 * o Power of 2 block 104 * o base suitably aligned to the power 105 */ 106 if (type > MTRR_TYPE_WRCOMB || size < (1 << (17 - PAGE_SHIFT)) 107 || (size & ~(size - 1)) - size || (base & (size - 1))) 108 return -EINVAL; 109 return 0; 110 } 111 112 const struct mtrr_ops amd_mtrr_ops = { 113 .vendor = X86_VENDOR_AMD, 114 .set = amd_set_mtrr, 115 .get = amd_get_mtrr, 116 .get_free_region = generic_get_free_region, 117 .validate_add_page = amd_validate_add_page, 118 .have_wrcomb = positive_have_wrcomb, 119 }; 120