[PATCH v2 3/6] 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: Paul Burton <paulburton@xxxxxxxxxx>
Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
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".
---
 drivers/dma/dw/core.c | 17 +++++++++++++++++
 drivers/dma/dw/regs.h | 18 ++++++++++--------
 2 files changed, 27 insertions(+), 8 deletions(-)

diff --git a/drivers/dma/dw/core.c b/drivers/dma/dw/core.c
index 21cb2a58dbd2..8bcd82c64478 100644
--- a/drivers/dma/dw/core.c
+++ b/drivers/dma/dw/core.c
@@ -1054,6 +1054,7 @@ int do_dma_probe(struct dw_dma_chip *chip)
 	struct dw_dma *dw = chip->dw;
 	struct dw_dma_platform_data *pdata;
 	bool			autocfg = false;
+	unsigned int		block_size = 0;
 	unsigned int		dw_params;
 	unsigned int		i;
 	int			err;
@@ -1184,6 +1185,18 @@ int do_dma_probe(struct dw_dma_chip *chip)
 			dwc->block_size = pdata->block_size;
 			dwc->nollp = !pdata->multi_block[i];
 		}
+
+		/*
+		 * Find maximum block size to be set as the DMA device maximum
+		 * segment size. By doing so we'll have size optimized SG-list
+		 * items for the channels with biggest block size. This won't
+		 * be a problem for the rest of the channels, since they will
+		 * still be able to split the requests up by allocating
+		 * multiple DW DMA LLP descriptors, which they would have done
+		 * anyway.
+		 */
+		if (dwc->block_size > block_size)
+			block_size = dwc->block_size;
 	}
 
 	/* Clear all interrupts on all channels. */
@@ -1220,6 +1233,10 @@ int do_dma_probe(struct dw_dma_chip *chip)
 			     BIT(DMA_MEM_TO_MEM);
 	dw->dma.residue_granularity = DMA_RESIDUE_GRANULARITY_BURST;
 
+	/* Block size corresponds to the maximum sg size */
+	dw->dma.dev->dma_parms = &dw->dma_parms;
+	dma_set_max_seg_size(dw->dma.dev, block_size);
+
 	err = dma_async_device_register(&dw->dma);
 	if (err)
 		goto err_dma_register;
diff --git a/drivers/dma/dw/regs.h b/drivers/dma/dw/regs.h
index 3fce66ecee7a..20037d64f961 100644
--- a/drivers/dma/dw/regs.h
+++ b/drivers/dma/dw/regs.h
@@ -8,6 +8,7 @@
  */
 
 #include <linux/bitops.h>
+#include <linux/device.h>
 #include <linux/interrupt.h>
 #include <linux/dmaengine.h>
 
@@ -308,16 +309,17 @@ static inline struct dw_dma_chan *to_dw_dma_chan(struct dma_chan *chan)
 }
 
 struct dw_dma {
-	struct dma_device	dma;
-	char			name[20];
-	void __iomem		*regs;
-	struct dma_pool		*desc_pool;
-	struct tasklet_struct	tasklet;
+	struct dma_device		dma;
+	struct device_dma_parameters	dma_parms;
+	char				name[20];
+	void __iomem			*regs;
+	struct dma_pool			*desc_pool;
+	struct tasklet_struct		tasklet;
 
 	/* channels */
-	struct dw_dma_chan	*chan;
-	u8			all_chan_mask;
-	u8			in_use;
+	struct dw_dma_chan		*chan;
+	u8				all_chan_mask;
+	u8				in_use;
 
 	/* Channel operations */
 	void	(*initialize_chan)(struct dw_dma_chan *dwc);
-- 
2.25.1