dmaengine: ioatdma: support latency tolerance report (LTR) for v3.4

IOATDMA 3.4 supports PCIe LTR mechanism. The registers are non-standard
PCIe LTR support. This needs to be setup in order to not suffer performance
impact and provide proper power management. The channel is set to active
when it is allocated, and to passive when it's freed.
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Vinod Koul <vkoul@kernel.org>

drivers/dma/ioat/init.c

@@ -638,6 +638,11 @@ static void ioat_free_chan_resources(struct dma_chan *c)
 	ioat_stop(ioat_chan);
 	ioat_reset_hw(ioat_chan);
 
+	/* Put LTR to idle */
+	if (ioat_dma->version >= IOAT_VER_3_4)
+		writeb(IOAT_CHAN_LTR_SWSEL_IDLE,
+			ioat_chan->reg_base + IOAT_CHAN_LTR_SWSEL_OFFSET);
+
 	spin_lock_bh(&ioat_chan->cleanup_lock);
 	spin_lock_bh(&ioat_chan->prep_lock);
 	descs = ioat_ring_space(ioat_chan);
@@ -727,6 +732,28 @@ static int ioat_alloc_chan_resources(struct dma_chan *c)
 	spin_unlock_bh(&ioat_chan->prep_lock);
 	spin_unlock_bh(&ioat_chan->cleanup_lock);
 
+	/* Setting up LTR values for 3.4 or later */
+	if (ioat_chan->ioat_dma->version >= IOAT_VER_3_4) {
+		u32 lat_val;
+
+		lat_val = IOAT_CHAN_LTR_ACTIVE_SNVAL |
+			IOAT_CHAN_LTR_ACTIVE_SNLATSCALE |
+			IOAT_CHAN_LTR_ACTIVE_SNREQMNT;
+		writel(lat_val, ioat_chan->reg_base +
+				IOAT_CHAN_LTR_ACTIVE_OFFSET);
+
+		lat_val = IOAT_CHAN_LTR_IDLE_SNVAL |
+			  IOAT_CHAN_LTR_IDLE_SNLATSCALE |
+			  IOAT_CHAN_LTR_IDLE_SNREQMNT;
+		writel(lat_val, ioat_chan->reg_base +
+				IOAT_CHAN_LTR_IDLE_OFFSET);
+
+		/* Select to active */
+		writeb(IOAT_CHAN_LTR_SWSEL_ACTIVE,
+		       ioat_chan->reg_base +
+		       IOAT_CHAN_LTR_SWSEL_OFFSET);
+	}
+
 	ioat_start_null_desc(ioat_chan);
 
 	/* check that we got off the ground */

drivers/dma/ioat/registers.h

@@ -253,4 +253,18 @@
 #define IOAT_CHAN_DRS_EN			0x0100
 #define IOAT_CHAN_DRS_AUTOWRAP			0x0200
 
+#define IOAT_CHAN_LTR_SWSEL_OFFSET		0xBC
+#define IOAT_CHAN_LTR_SWSEL_ACTIVE		0x0
+#define IOAT_CHAN_LTR_SWSEL_IDLE		0x1
+
+#define IOAT_CHAN_LTR_ACTIVE_OFFSET		0xC0
+#define IOAT_CHAN_LTR_ACTIVE_SNVAL		0x0000	/* 0 us */
+#define IOAT_CHAN_LTR_ACTIVE_SNLATSCALE		0x0800	/* 1us scale */
+#define IOAT_CHAN_LTR_ACTIVE_SNREQMNT		0x8000	/* snoop req enable */
+
+#define IOAT_CHAN_LTR_IDLE_OFFSET		0xC4
+#define IOAT_CHAN_LTR_IDLE_SNVAL		0x0258	/* 600 us */
+#define IOAT_CHAN_LTR_IDLE_SNLATSCALE		0x0800	/* 1us scale */
+#define IOAT_CHAN_LTR_IDLE_SNREQMNT		0x8000	/* snoop req enable */
+
 #endif /* _IOAT_REGISTERS_H_ */