[PATCH v3 07/10] dmaengine: dw: Set DMA device max segment size parameter

[Serge Semin]

Maximum block size DW DMAC configuration corresponds to the max segment
size DMA parameter in the DMA core subsystem notation. Lets set it with a
value specific to the probed DW DMA controller. It shall help the DMA
clients to create size-optimized SG-list items for the controller. This in
turn will cause less dw_desc allocations, less LLP reinitializations,
better DMA device performance.

Signed-off-by: Serge Semin <Sergey.Semin@xxxxxxxxxxxxxxxxxxxx>
Cc: Alexey Malahov <Alexey.Malahov@xxxxxxxxxxxxxxxxxxxx>
Cc: Thomas Bogendoerfer <tsbogend@xxxxxxxxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Rob Herring <robh+dt@xxxxxxxxxx>
Cc: linux-mips@xxxxxxxxxxxxxxx
Cc: devicetree@xxxxxxxxxxxxxxx

---

Changelog v2:
- This is a new patch created in place of the dropped one:
  "dmaengine: dw: Add LLP and block size config accessors".

Changelog v3:
- Use the block_size found for the very first channel instead of looking for
  the maximum of maximum block sizes.
- Don't define device-specific device_dma_parameters object, since it has
  already been defined by the platform device core.
---
 drivers/dma/dw/core.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/dma/dw/core.c b/drivers/dma/dw/core.c
index 33e99d95b3d3..fb95920c429e 100644
--- a/drivers/dma/dw/core.c
+++ b/drivers/dma/dw/core.c
@@ -1229,6 +1229,13 @@ int do_dma_probe(struct dw_dma_chip *chip)
 			     BIT(DMA_MEM_TO_MEM);
 	dw->dma.residue_granularity = DMA_RESIDUE_GRANULARITY_BURST;
 
+	/*
+	 * For now there is no hardware with non uniform maximum block size
+	 * across all of the device channels, so we set the maximum segment
+	 * size as the block size found for the very first channel.
+	 */
+	dma_set_max_seg_size(dw->dma.dev, dw->chan[0].block_size);
+
 	err = dma_async_device_register(&dw->dma);
 	if (err)
 		goto err_dma_register;
-- 
2.26.2