[PATCH v2 0/4] ARC: allow to use IOC and non-IOC DMA devices simultaneously

[Eugeniy Paltsev]

The ARC HS processor provides an IOC port (I/O coherency bus
interface) that allows external devices such as DMA devices
to access memory through the cache hierarchy, providing
coherency between I/O transactions and the complete memory
hierarchy.

Some recent SoC with ARC HS (like HSDK) allow to select bus
port (IOC or non-IOC port) for connecting DMA devices in runtime.

With this patch we can use both HW-coherent and regular DMA
peripherals simultaneously.

NOTE:
This patch series was stress tested on HSDK with iperf3 (ethernet)
and bonie++ (usb and sdio) in three configurations:
 * IOC enabled globaly
 * IOC disabled globaly
 * IOC enabled partially (USB & SDIO are connected via IOC AXI port,
   ethernet is connected to DDR AXI port (non-IOC port) 

NOTE:
If you want to test some device without IOC it is not enough
to remove "dma-coherent" property from dts. You had to remap this
device to regular DDR AXI port intead of IOC AXI port.
You also need to apply 3 following patches firstly:
https://www.mail-archive.com/linux-snps-arc@xxxxxxxxxxxxxxxxxxx/msg03865.html
https://www.mail-archive.com/linux-snps-arc@xxxxxxxxxxxxxxxxxxx/msg03889.html
https://www.mail-archive.com/linux-snps-arc@xxxxxxxxxxxxxxxxxxx/msg03887.html

NOTE:
We don't touch any aperture configuration in this patch series. So we
don't switch any devices between IOC and non-IOC AXI ports on any board.
It can be done later if it is required.

Changes v1->v2 (Thanks to Christoph):
 * Don't select DMA_DIRECT_OPS explicitly as it is already selected by
   DMA_NONCOHERENT_OPS
 * Remove check for HIGHMEM pages from arch_dma_{alloc, free}

Eugeniy Paltsev (4):
  ARC: DTS: mark DMA devices connected through IOC port as dma-coherent
  ARC: allow to use IOC and non-IOC DMA devices simultaneously
  ARC: IOC: panic if both IOC and ZONE_HIGHMEM enabled
  ARC: don't check for HIGHMEM pages in arch_dma_alloc

 arch/arc/boot/dts/axc003.dtsi      | 26 ++++++++++++++++
 arch/arc/boot/dts/axc003_idu.dtsi  | 26 ++++++++++++++++
 arch/arc/boot/dts/hsdk.dts         |  4 +++
 arch/arc/include/asm/dma-mapping.h | 13 ++++++++
 arch/arc/mm/cache.c                | 30 +++++++++---------
 arch/arc/mm/dma.c                  | 62 +++++++++++++++++++-------------------
 6 files changed, 115 insertions(+), 46 deletions(-)
 create mode 100644 arch/arc/include/asm/dma-mapping.h

-- 
2.14.4