On Wed, Feb 15, 2017 at 12:55 PM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote: > On Tue, Feb 14, 2017 at 11:03 PM, Anup Patel <anup.patel@xxxxxxxxxxxx> wrote: >> On Wed, Feb 15, 2017 at 12:13 PM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote: >>> On Tue, Feb 14, 2017 at 10:25 PM, Anup Patel <anup.patel@xxxxxxxxxxxx> wrote: >>>> On Tue, Feb 14, 2017 at 10:04 PM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote: >>>>> On Mon, Feb 13, 2017 at 10:51 PM, Anup Patel <anup.patel@xxxxxxxxxxxx> wrote: >>>>>> The Broadcom stream buffer accelerator (SBA) provides offloading >>>>>> capabilities for RAID operations. This SBA offload engine is >>>>>> accessible via Broadcom SoC specific ring manager. >>>>>> >>>>>> This patch adds Broadcom SBA RAID driver which provides one >>>>>> DMA device with RAID capabilities using one or more Broadcom >>>>>> SoC specific ring manager channels. The SBA RAID driver in its >>>>>> current shape implements memcpy, xor, and pq operations. >>>>>> >>>>>> Signed-off-by: Anup Patel <anup.patel@xxxxxxxxxxxx> >>>>>> Reviewed-by: Ray Jui <ray.jui@xxxxxxxxxxxx> >>>>>> --- >>>>>> drivers/dma/Kconfig | 13 + >>>>>> drivers/dma/Makefile | 1 + >>>>>> drivers/dma/bcm-sba-raid.c | 1694 ++++++++++++++++++++++++++++++++++++++++++++ >>>>>> 3 files changed, 1708 insertions(+) >>>>>> create mode 100644 drivers/dma/bcm-sba-raid.c >>>>>> >>>>>> diff --git a/drivers/dma/Kconfig b/drivers/dma/Kconfig >>>>>> index 263495d..bf8fb84 100644 >>>>>> --- a/drivers/dma/Kconfig >>>>>> +++ b/drivers/dma/Kconfig >>>>>> @@ -99,6 +99,19 @@ config AXI_DMAC >>>>>> controller is often used in Analog Device's reference designs for FPGA >>>>>> platforms. >>>>>> >>>>>> +config BCM_SBA_RAID >>>>>> + tristate "Broadcom SBA RAID engine support" >>>>>> + depends on (ARM64 && MAILBOX && RAID6_PQ) || COMPILE_TEST >>>>>> + select DMA_ENGINE >>>>>> + select DMA_ENGINE_RAID >>>>>> + select ASYNC_TX_ENABLE_CHANNEL_SWITCH >>>>> >>>>> I thought you agreed to drop this. Its usage is broken. >>>> >>>> If ASYNC_TX_ENABLE_CHANNEL_SWITCH is not selected >>>> then async_dma_find_channel() will only try to find channel >>>> with DMA_ASYNC_TX capability. >>>> >>>> The DMA_ASYNC_TX capability is set by >>>> dma_async_device_register() when all Async Tx >>>> capabilities are supported by a DMA devices namely >>>> DMA_INTERRUPT, DMA_MEMCPY, DMA_XOR, >>>> DMA_XOR_VAL, DMA_PQ, and DMA_PQ_VAL. >>>> >>>> We only support DMA_MEMCPY, DMA_XOR, and >>>> DMA_PQ capabilities in BCM-SBA-RAID driver so >>>> DMA_ASYNC_TX capability is never set for the >>>> DMA device registered by BCM-SBA-RAID driver. >>>> >>>> Due to above, if ASYNC_TX_ENABLE_CHANNEL_SWITCH >>>> is not selected then Async Tx APIs fail to find DMA >>>> channel provided by BCM-SBA-RAID hence the >>>> option ASYNC_TX_ENABLE_CHANNEL_SWITCH is >>>> required for BCM-SBA-RAID. >>>> >>>> The DMA mappings are violated by channel switching >>>> only if we switch form DMA channel A to DMA channel >>>> B and both these DMA channels have different underlying >>>> "struct device". In most of the cases DMA mappings >>>> are not violated because DMA channels having >>>> Async Tx capabilities are provided using same >>>> underlying "struct device". >>> >>> No, fix the infrastructure. Do not put local hack in your driver for >>> this global problem [1]. >> >> There is no hack in the driver. We need >> ASYNC_TX_ENABLE_CHANNEL_SWITCH >> based on current state of dmaengine framework. >> >> The framework should be fixed as separate patchset. >> >> We have other RAID drivers such as xgene-dma and >> mv_xor_v2 who also require >> ASYNC_TX_ENABLE_CHANNEL_SWITCH due >> to same reason. >> >> Fixing the framework and improving framework is >> a ongoing process. I don't see why that should >> stop this patchset. >> > > Because this driver is turning on a dangerous compile time option and > is not using the functionality. If this silicon IP block appears in > another product in the future paired with another DMA engine then the > assumptions about a safe/single dma-device is violated. > > The realization of how async_tx was breaking DMA mapping api > assumptions came after some of these dma-drivers were added to the > kernel. We should stop making the problem worse. > > I should have submitted a patch like the below at the time we > discovered this problem, but unfortunately it languished when I > stopped maintaining the iop-adma and ioat drivers. > > diff --git a/drivers/dma/Kconfig b/drivers/dma/Kconfig > index 263495d0adbd..6b30eb9ad125 100644 > --- a/drivers/dma/Kconfig > +++ b/drivers/dma/Kconfig > @@ -35,6 +35,7 @@ comment "DMA Devices" > > #core > config ASYNC_TX_ENABLE_CHANNEL_SWITCH > + depends on BROKEN > bool > > config ARCH_HAS_ASYNC_TX_FIND_CHANNEL Instead of selecting ASYNC_TX_ENABLE_CHANNEL_SWITCH, we can select the following in BCM_SBA_RAID config option: 1. ASYNC_TX_DISABLE_XOR_VAL 2. ASYNC_TX_DISABLE_PQ_VAL This will satisfy the needs of dma_async_device_register() when ASYNC_TX_ENABLE_CHANNEL_SWITCH is not selected. Will this be acceptable ?? Regards, Anup
