[PATCH v7 09/11] dmaengine: dw: Initialize min and max burst DMA device capability

Serge Semin
2020-07-09T22:46:42Z

According to the DW APB DMAC data book the minimum burst transaction
length is 1 and it's true for any version of the controller since
isn't parametrised in the coreAssembler so can't be changed at the
IP-core synthesis stage. The maximum burst transaction can vary from
channel to channel and from controller to controller depending on a
IP-core parameter the system engineer activated during the IP-core
synthesis. Let's initialise both min_burst and max_burst members of the
DMA controller descriptor with extreme values so the DMA clients could
use them to properly optimize the DMA requests. The channels and
controller-specific max_burst length initialization will be introduced
by the follow-up patches.

Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: linux-mips@vger.kernel.org
Cc: devicetree@vger.kernel.org

---

Changelog v4:
- This is a new patch suggested by Andy.

Changelog v5:
- Introduce macro with extreme min and max burst length supported by the
DW DMA controller.
- Initialize max_burst length capability with extreme burst length supported
by the DW DMAC IP-core.
---
drivers/dma/dw/core.c | 2 ++
include/linux/platform_data/dma-dw.h | 2 ++
2 files changed, 4 insertions(+)

diff --git a/drivers/dma/dw/core.c b/drivers/dma/dw/core.c
index ceded21537e2..4887aa2fc73c 100644
--- a/drivers/dma/dw/core.c
+++ b/drivers/dma/dw/core.c
@@ -1229,6 +1229,8 @@ int do_dma_probe(struct dw_dma_chip *chip)
dw->dma.device_issue_pending = dwc_issue_pending;

/* DMA capabilities */
+ dw->dma.min_burst = DW_DMA_MIN_BURST;
+ dw->dma.max_burst = DW_DMA_MAX_BURST;
dw->dma.src_addr_widths = DW_DMA_BUSWIDTHS;
dw->dma.dst_addr_widths = DW_DMA_BUSWIDTHS;
dw->dma.directions = BIT(DMA_DEV_TO_MEM) | BIT(DMA_MEM_TO_DEV) |
diff --git a/include/linux/platform_data/dma-dw.h b/include/linux/platform_data/dma-dw.h
index f3eaf9ec00a1..369e41e9dcc9 100644
--- a/include/linux/platform_data/dma-dw.h
+++ b/include/linux/platform_data/dma-dw.h
@@ -12,6 +12,8 @@

#define DW_DMA_MAX_NR_MASTERS 4
#define DW_DMA_MAX_NR_CHANNELS 8
+#define DW_DMA_MIN_BURST 1
+#define DW_DMA_MAX_BURST 256

/**
* struct dw_dma_slave - Controller-specific information about a slave
--
2.26.2