[PATCH v3 3/4] dmaengine: Add Broadcom SBA RAID driver

On Fri, Feb 10, 2017 at 11:20 PM, Dan Williams [off-list ref] wrote:

On Fri, Feb 10, 2017 at 1:07 AM, Anup Patel [off-list ref] wrote:

quoted

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 <redacted>
Reviewed-by: Ray Jui <redacted>
---
 drivers/dma/Kconfig        |   13 +
 drivers/dma/Makefile       |    1 +
 drivers/dma/bcm-sba-raid.c | 1711 ++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 1725 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

ASYNC_TX_ENABLE_CHANNEL_SWITCH violates the DMA mapping API and
Russell has warned it's especially problematic on ARM [1].  If you
need channel switching for this offload engine to be useful then you
need to move DMA mapping and channel switching responsibilities to MD
itself.

[1]: http://lists.infradead.org/pipermail/linux-arm-kernel/2011-January/036753.html

In case of BCM-SBA-RAID, the underlying "struct device" for each
DMA channel is the mailbox controller "struct device" (i.e. Ring
Manager device). This is because Ring Manager HW is the front
facing device which we program to submit work to BCM-SBA-RAID
HW.

This means DMA channels provided by BCM-SBA-RAID driver
will use same "struct device" for DMA mappings hence channel
switching between BCM-SBA-RAID DMA channels is safe.

Due to above, we can safely enable
ASYNC_TX_ENABLE_CHANNEL_SWITCH option for
BCM-SBA-RAID driver.

Regards,
Anup