Merge branch 'mvpp2-tx-flow-control'

Stefan Chulski says:

====================
net: mvpp2: Add TX Flow Control support

Armada hardware has a pause generation mechanism in GOP (MAC).
The GOP generate flow control frames based on an indication programmed in Ports Control 0 Register. There is a bit per port.
However assertion of the PortX Pause bits in the ports control 0 register only sends a one time pause.
To complement the function the GOP has a mechanism to periodically send pause control messages based on periodic counters.
This mechanism ensures that the pause is effective as long as the Appropriate PortX Pause is asserted.

Problem is that Packet Processor that actually can drop packets due to lack of resources not connected to the GOP flow control generation mechanism.
To solve this issue Armada has firmware running on CM3 CPU dedicated for Flow Control support.
Firmware monitors Packet Processor resources and asserts XON/XOFF by writing to Ports Control 0 Register.

MSS shared SRAM memory used to communicate between CM3 firmware and PP2 driver.
During init PP2 driver informs firmware about used BM pools, RXQs, congestion and depletion thresholds.

The pause frames are generated whenever congestion or depletion in resources is detected.
The back pressure is stopped when the resource reaches a sufficient level.
So the congestion/depletion and sufficient level implement a hysteresis that reduces the XON/XOFF toggle frequency.

Packet Processor v23 hardware introduces support for RX FIFO fill level monitor.
Patch "add PPv23 version definition" to differ between v23 and v22 hardware.
Patch "add TX FC firmware check" verifies that CM3 firmware supports Flow Control monitoring.

v12 --> v13
- Remove bm_underrun_protect module_param

v11 --> v12
- Improve warning message in "net: mvpp2: add TX FC firmware check" patch

v10 --> v11
- Improve "net: mvpp2: add CM3 SRAM memory map" comment
- Move condition check to 'net: mvpp2: always compare hw-version vs MVPP21' patch

v9 --> v10
- Add CM3 SRAM description to PPv2 documentation

v8 --> v9
- Replace generic pool allocation with devm_ioremap_resource

v7 --> v8
- Reorder "always compare hw-version vs MVPP21" and "add PPv23 version definition" commits
- Typo fixes
- Remove condition fix from "add RXQ flow control configurations"

v6 --> v7
- Reduce patch set from 18 to 15 patches
 - Documentation change combined into a single patch
 - RXQ and BM size change combined into a single patch
 - Ring size change check moved into "add RXQ flow control configurations" commit

v5 --> v6
- No change

v4 --> v5
- Add missed Signed-off
- Fix warnings in patches 3 and 12
- Add revision requirement to warning message
- Move mss_spinlock into RXQ flow control configurations patch
- Improve FCA RXQ non occupied descriptor threshold commit message

v3 --> v4
- Remove RFC tag

v2 --> v3
- Remove inline functions
- Add PPv2.3 description into marvell-pp2.txt
- Improve mvpp2_interrupts_mask/unmask procedure
- Improve FC enable/disable procedure
- Add priv->sram_pool check
- Remove gen_pool_destroy call
- Reduce Flow Control timer to x100 faster

v1 --> v2
- Add memory requirements information
- Add EPROBE_DEFER if of_gen_pool_get return NULL
- Move Flow control configuration to mvpp2_mac_link_up callback
====================

Signed-off-by: David S. Miller <davem@davemloft.net>