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author | Linus Torvalds <torvalds@linux-foundation.org> | 2014-12-13 01:11:12 +0100 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2014-12-13 01:11:12 +0100 |
commit | f96fe225677b3efb74346ebd56fafe3997b02afa (patch) | |
tree | 75afbbfd687d678587de244b075a6f836c206425 /Documentation | |
parent | Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/ide (diff) | |
parent | Merge branch 'gem' (diff) | |
download | linux-f96fe225677b3efb74346ebd56fafe3997b02afa.tar.xz linux-f96fe225677b3efb74346ebd56fafe3997b02afa.zip |
Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net
Pull another networking update from David Miller:
"Small follow-up to the main merge pull from the other day:
1) Alexander Duyck's DMA memory barrier patch set.
2) cxgb4 driver fixes from Karen Xie.
3) Add missing export of fixed_phy_register() to modules, from Mark
Salter.
4) DSA bug fixes from Florian Fainelli"
* git://git.kernel.org/pub/scm/linux/kernel/git/davem/net: (24 commits)
net/macb: add TX multiqueue support for gem
linux/interrupt.h: remove the definition of unused tasklet_hi_enable
jme: replace calls to redundant function
net: ethernet: davicom: Allow to select DM9000 for nios2
net: ethernet: smsc: Allow to select SMC91X for nios2
cxgb4: Add support for QSA modules
libcxgbi: fix freeing skb prematurely
cxgb4i: use set_wr_txq() to set tx queues
cxgb4i: handle non-pdu-aligned rx data
cxgb4i: additional types of negative advice
cxgb4/cxgb4i: set the max. pdu length in firmware
cxgb4i: fix credit check for tx_data_wr
cxgb4i: fix tx immediate data credit check
net: phy: export fixed_phy_register()
fib_trie: Fix trie balancing issue if new node pushes down existing node
vlan: Add ability to always enable TSO/UFO
r8169:update rtl8168g pcie ephy parameter
net: dsa: bcm_sf2: force link for all fixed PHY devices
fm10k/igb/ixgbe: Use dma_rmb on Rx descriptor reads
r8169: Use dma_rmb() and dma_wmb() for DescOwn checks
...
Diffstat (limited to 'Documentation')
-rw-r--r-- | Documentation/memory-barriers.txt | 42 |
1 files changed, 42 insertions, 0 deletions
diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt index 7ee2ae6d5451..70a09f8a0383 100644 --- a/Documentation/memory-barriers.txt +++ b/Documentation/memory-barriers.txt @@ -1633,6 +1633,48 @@ There are some more advanced barrier functions: operations" subsection for information on where to use these. + (*) dma_wmb(); + (*) dma_rmb(); + + These are for use with consistent memory to guarantee the ordering + of writes or reads of shared memory accessible to both the CPU and a + DMA capable device. + + For example, consider a device driver that shares memory with a device + and uses a descriptor status value to indicate if the descriptor belongs + to the device or the CPU, and a doorbell to notify it when new + descriptors are available: + + if (desc->status != DEVICE_OWN) { + /* do not read data until we own descriptor */ + dma_rmb(); + + /* read/modify data */ + read_data = desc->data; + desc->data = write_data; + + /* flush modifications before status update */ + dma_wmb(); + + /* assign ownership */ + desc->status = DEVICE_OWN; + + /* force memory to sync before notifying device via MMIO */ + wmb(); + + /* notify device of new descriptors */ + writel(DESC_NOTIFY, doorbell); + } + + The dma_rmb() allows us guarantee the device has released ownership + before we read the data from the descriptor, and he dma_wmb() allows + us to guarantee the data is written to the descriptor before the device + can see it now has ownership. The wmb() is needed to guarantee that the + cache coherent memory writes have completed before attempting a write to + the cache incoherent MMIO region. + + See Documentation/DMA-API.txt for more information on consistent memory. + MMIO WRITE BARRIER ------------------ |