Lines Matching +full:no +full:- +full:memory +full:- +full:wc
1 .. SPDX-License-Identifier: GPL-2.0
7 x86 Page Attribute Table (PAT) allows for setting the memory attribute at the
9 for setting of memory types over physical address ranges. However, PAT is
11 and also due to the fact that there are no hardware limitations on number of
13 not having memory type aliasing for the same physical memory with multiple
16 PAT allows for different types of memory attributes. The most commonly used
20 WB Write-back
22 WC Write-combined
23 WT Write-through
24 UC- Uncached Minus
31 There are many different APIs in the kernel that allows setting of memory
34 their intended usage and their memory attribute relationships. Internally,
38 +------------------------+----------+--------------+------------------+
40 +------------------------+----------+--------------+------------------+
41 | ioremap | -- | UC- | UC- |
42 +------------------------+----------+--------------+------------------+
43 | ioremap_cache | -- | WB | WB |
44 +------------------------+----------+--------------+------------------+
45 | ioremap_uc | -- | UC | UC |
46 +------------------------+----------+--------------+------------------+
47 | ioremap_wc | -- | -- | WC |
48 +------------------------+----------+--------------+------------------+
49 | ioremap_wt | -- | -- | WT |
50 +------------------------+----------+--------------+------------------+
51 | set_memory_uc, | UC- | -- | -- |
53 +------------------------+----------+--------------+------------------+
54 | set_memory_wc, | WC | -- | -- |
56 +------------------------+----------+--------------+------------------+
57 | set_memory_wt, | WT | -- | -- |
59 +------------------------+----------+--------------+------------------+
60 | pci sysfs resource | -- | -- | UC- |
61 +------------------------+----------+--------------+------------------+
62 | pci sysfs resource_wc | -- | -- | WC |
64 +------------------------+----------+--------------+------------------+
65 | pci proc | -- | -- | UC- |
67 +------------------------+----------+--------------+------------------+
68 | pci proc | -- | -- | WC |
70 +------------------------+----------+--------------+------------------+
71 | /dev/mem | -- | WB/WC/UC- | WB/WC/UC- |
72 | read-write | | | |
73 +------------------------+----------+--------------+------------------+
74 | /dev/mem | -- | UC- | UC- |
76 +------------------------+----------+--------------+------------------+
77 | /dev/mem | -- | WB/WC/UC- | WB/WC/UC- |
81 +------------------------+----------+--------------+------------------+
82 | /dev/mem | -- | WB | WB |
84 | no alias to this area | | | |
87 +------------------------+----------+--------------+------------------+
88 | /dev/mem | -- | -- | UC- |
90 | no alias to this area | | | |
93 +------------------------+----------+--------------+------------------+
112 In addition, step 2 internally tracks the region as UC or WC in memtype
113 list in order to ensure no conflicting mapping.
120 MTRR effects on PAT / non-PAT systems
123 The following table provides the effects of using write-combining MTRRs when
124 using ioremap*() calls on x86 for both non-PAT and PAT systems. Ideally
126 be a no-op on PAT enabled systems. The region over which a arch_phys_wc_add()
127 is made, should already have been ioremapped with WC attributes or PAT entries,
129 combine areas of IO memory desired to remain uncacheable with areas where
130 write-combining is desirable should consider use of ioremap_uc() followed by
131 set_memory_wc() to white-list effective write-combined areas. Such use is
132 nevertheless discouraged as the effective memory type is considered
134 with size-constrained regions where otherwise MTRR write-combining would
139 MTRR Non-PAT PAT Linux ioremap value Effective memory type
141 PAT Non-PAT | PAT
145 WC 000 WB _PAGE_CACHE_MODE_WB WC | WC
146 WC 001 WC _PAGE_CACHE_MODE_WC WC* | WC
147 WC 010 UC- _PAGE_CACHE_MODE_UC_MINUS WC* | UC
148 WC 011 UC _PAGE_CACHE_MODE_UC UC | UC
153 .. note:: -- in the above table mean "Not suggested usage for the API". Some
154 of the --'s are strictly enforced by the kernel. Some others are not really
157 For ioremap and pci access through /sys or /proc - The actual type returned
160 return uncached mapping in place of write-combine requested.
162 set_memory_[uc|wc|wt] and set_memory_wb should be used in pairs, where driver
163 will first make a region uc, wc or wt and switch it back to wb after use.
168 Drivers should use ioremap_[uc|wc] to access PCI BARs with [uc|wc] access
171 Drivers should use set_memory_[uc|wc|wt] to set access type for RAM ranges.
179 # mount -t debugfs debugfs /sys/kernel/debug
182 uncached-minus @ 0x7fadf000-0x7fae0000
183 uncached-minus @ 0x7fb19000-0x7fb1a000
184 uncached-minus @ 0x7fb1a000-0x7fb1b000
185 uncached-minus @ 0x7fb1b000-0x7fb1c000
186 uncached-minus @ 0x7fb1c000-0x7fb1d000
187 uncached-minus @ 0x7fb1d000-0x7fb1e000
188 uncached-minus @ 0x7fb1e000-0x7fb25000
189 uncached-minus @ 0x7fb25000-0x7fb26000
190 uncached-minus @ 0x7fb26000-0x7fb27000
191 uncached-minus @ 0x7fb27000-0x7fb28000
192 uncached-minus @ 0x7fb28000-0x7fb2e000
193 uncached-minus @ 0x7fb2e000-0x7fb2f000
194 uncached-minus @ 0x7fb2f000-0x7fb30000
195 uncached-minus @ 0x7fb31000-0x7fb32000
196 uncached-minus @ 0x80000000-0x90000000
209 configurations. The PAT MSR must be updated by Linux in order to support WC
211 by the firmware. Note, Xen enables WC attribute in the PAT MSR for guests.
216 E E MTRR -> PAT init Enabled OS
217 E D MTRR -> PAT init Disabled -
218 D E MTRR -> PAT disable Disabled BIOS
219 D D MTRR -> PAT disable Disabled -
220 - np/E PAT -> PAT disable Disabled BIOS
221 - np/D PAT -> PAT disable Disabled -
222 E !P/E MTRR -> PAT init Disabled BIOS
223 D !P/E MTRR -> PAT disable Disabled BIOS
224 !M !P/E MTRR stub -> PAT disable Disabled BIOS