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

From: Vineet Gupta
Date: Mon Aug 13 2018 - 12:19:27 EST

On 07/30/2018 09:26 AM, Eugeniy Paltsev wrote:
> 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.

You didn't pay attention to my previous comment on this !
IOC port can be considered a micro-architecture optimization (an important one
though). The main thing is hardware snooping DMA transactions which enabled IOC in
first place.

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

Again you mention the port but none of your 4 patches actually touch the port
itself in programming it.

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

Why are we not doing that for the GPU as part of this series.

> You also need to apply 3 following patches firstly:
> 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
> * 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