usb: renesas_usbhs: Revise the binding document about the dma-names

Since the DT should describe the hardware (not the driver limitation),
This patch revises the binding document about the dma-names to change
simple numbering as "ch%d" instead of "tx<n>" and "rx<n>".

Also this patch fixes the actual code of renesas_usbhs driver to handle
the new dma-names.
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Felipe Balbi <balbi@ti.com>

Documentation/devicetree/bindings/usb/renesas_usbhs.txt

@@ -15,10 +15,8 @@ Optional properties:
   - phys: phandle + phy specifier pair
   - phy-names: must be "usb"
   - dmas: Must contain a list of references to DMA specifiers.
-  - dma-names : Must contain a list of DMA names:
-   - tx0 ... tx<n>
-   - rx0 ... rx<n>
-    - This <n> means DnFIFO in USBHS module.
+  - dma-names : named "ch%d", where %d is the channel number ranging from zero
+                to the number of channels (DnFIFOs) minus one.
 
 Example:
 	usbhs: usb@e6590000 {

drivers/usb/renesas_usbhs/fifo.c

@@ -1227,15 +1227,21 @@ static void usbhsf_dma_init_dt(struct device *dev, struct usbhs_fifo *fifo,
 {
 	char name[16];
 
-	snprintf(name, sizeof(name), "tx%d", channel);
-	fifo->tx_chan = dma_request_slave_channel_reason(dev, name);
-	if (IS_ERR(fifo->tx_chan))
-		fifo->tx_chan = NULL;
-
-	snprintf(name, sizeof(name), "rx%d", channel);
-	fifo->rx_chan = dma_request_slave_channel_reason(dev, name);
-	if (IS_ERR(fifo->rx_chan))
-		fifo->rx_chan = NULL;
+	/*
+	 * To avoid complex handing for DnFIFOs, the driver uses each
+	 * DnFIFO as TX or RX direction (not bi-direction).
+	 * So, the driver uses odd channels for TX, even channels for RX.
+	 */
+	snprintf(name, sizeof(name), "ch%d", channel);
+	if (channel & 1) {
+		fifo->tx_chan = dma_request_slave_channel_reason(dev, name);
+		if (IS_ERR(fifo->tx_chan))
+			fifo->tx_chan = NULL;
+	} else {
+		fifo->rx_chan = dma_request_slave_channel_reason(dev, name);
+		if (IS_ERR(fifo->rx_chan))
+			fifo->rx_chan = NULL;
+	}
 }
 
 static void usbhsf_dma_init(struct usbhs_priv *priv, struct usbhs_fifo *fifo,