On Mon, 30 Apr 2012 13:31:41 -0700 Dan Williams <dan.j.williams@xxxxxxxxx> wrote: > [ adding Russell and Neil for comment about the proposed change to async_tx ] I've managed to avoid learning much about the internal details of async_tx and adma but I thought I'd have a quick look. Doesn't this Kconfig change simply disable ASYNC_TX_DMA on any device that selects ASNC_TX_ENABLE_CHANNEL_SWITCH. i.e. INTEL_IOP_ADMA FSL_DMA MX_XOR AMCC_PPC440_SPA_ADMA Is that what you want to do? Disable all of those? I guess if they don't work then that is the right thing to do.... NeilBrown > > On Mon, Apr 30, 2012 at 3:05 AM, Rajasekhar Pulluru > <pullururajasekhar@xxxxxxxxx> wrote: > > Hi, > > > > I am trying to understand how are hardware xor engine's utilized by > > async_tx module. I don't get the exact link that connects async_tx and > > hardware xor engine. > > Could someone help me understand it. > > > > Registration of a RAID HW XOR engine happens in > > drivers/dma/<soc-xor.c> using dma_async_device_register(). Does this > > registration function connect the async_tx api's > > to use the HW XOR engine? > > Yes, the channel registers its capabilities with dmaengine, and then > async_tx asks dmaengine (via dma_find_channel) for a resource to carry > out the operation(s). > > > Or is there anything we need to support to > > make async_tx api's to take advantage of the hardware XOR engine? > > Registration with dma engine should be all that is needed, but a word > of caution that the channel switching mechanism has been found to be > incompatible with the dma mapping api. So, unless your dma channel > supports all the operations needed for raid, do not rely on async_tx's > channel switching capabilities. > > An architecture where this is known to be a problem is ARM, but I > wonder if we should take the following global step until this is fixed > properly? > > diff --git a/drivers/dma/Kconfig b/drivers/dma/Kconfig > index cf9da36..b812b6b 100644 > --- a/drivers/dma/Kconfig > +++ b/drivers/dma/Kconfig > @@ -280,6 +280,7 @@ config NET_DMA > config ASYNC_TX_DMA > bool "Async_tx: Offload support for the async_tx api" > depends on DMA_ENGINE > + depends on !ASYNC_TX_ENABLE_CHANNEL_SWITCH > help > This allows the async_tx api to take advantage of offload engines for > memcpy, memset, xor, and raid6 p+q operations. If your platform has
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