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authorFlorian Fainelli <f.fainelli@gmail.com>2018-03-13 14:45:07 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2018-03-31 18:12:34 +0200
commitcff88ba2a0935294a23f3f6c94960e2c2e79d66b (patch)
tree6476af7a2f55e47329a61cdb776501673afafa0a /Makefile
parent5ebbc4521c15caa6a36a8df01d0642b58130df95 (diff)
net: systemport: Rewrite __bcm_sysport_tx_reclaim()
[ Upstream commit 484d802d0f2f29c335563fcac2a8facf174a1bbc ] There is no need for complex checking between the last consumed index and current consumed index, a simple subtraction will do. This also eliminates the possibility of a permanent transmit queue stall under the following conditions: - one CPU bursts ring->size worth of traffic (up to 256 buffers), to the point where we run out of free descriptors, so we stop the transmit queue at the end of bcm_sysport_xmit() - because of our locking, we have the transmit process disable interrupts which means we can be blocking the TX reclamation process - when TX reclamation finally runs, we will be computing the difference between ring->c_index (last consumed index by SW) and what the HW reports through its register - this register is masked with (ring->size - 1) = 0xff, which will lead to stripping the upper bits of the index (register is 16-bits wide) - we will be computing last_tx_cn as 0, which means there is no work to be done, and we never wake-up the transmit queue, leaving it permanently disabled A practical example is e.g: ring->c_index aka last_c_index = 12, we pushed 256 entries, HW consumer index = 268, we mask it with 0xff = 12, so last_tx_cn == 0, nothing happens. Fixes: 80105befdb4b ("net: systemport: add Broadcom SYSTEMPORT Ethernet MAC driver") Signed-off-by: Florian Fainelli <f.fainelli@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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