drivers: udc_ambiq: added support for double endpoint buffer

implements option to enable double endpoint buffer to improve throughtput
for non-control endpoints.

Signed-off-by: Chew Zeh Yang <zeon.chew@ambiq.com>

drivers/usb/udc/Kconfig.ambiq

@@ -56,4 +56,20 @@ config UDC_AMBIQ_PIO_MODE
 	  Select this option when cache coherency handling is to be avoided.
 endchoice
 
+config UDC_AMBIQ_DEB_ENABLE
+	hex "EP Double Buffer Enable"
+	default 0x0000
+	depends on SOC_SERIES_APOLLO5X
+	help
+	  Double Endpoint Buffer acceleration (DEB) is doubles an EP's FIFO size so
+	  that USB transfer could continue to happen while waiting for DMA/CPU to
+	  load/unload data from the EP FIFO. This hex value is a bitmap of endpoints
+	  for DEB to be enabled. BIT0-4 represents OUT_EP 1-5, while BIT16-20
+	  represents IN_EP 1-5. Take note that this feature is limited by total EP
+	  FIFO size. Proper calculation should be done before enabling DEB such that
+	  the total usage of FIFO for all endpoint doesn't exceed the FIFO available
+	  on SoC. The list of Soc with its FIFO size is listed below. The FIFO size
+	  here includes 128 bytes required by control endpoints.
+	  - Apollo510: (4096 Bytes FIFO)
+
 endif # UDC_AMBIQ

drivers/usb/udc/udc_ambiq.c

@@ -565,6 +565,29 @@ static int init_apollo5x(const struct udc_ambiq_data *priv)
 }
 #endif
 
+#if CONFIG_UDC_AMBIQ_DEB_ENABLE
+static void init_double_buffers(const struct udc_ambiq_data *priv)
+{
+	uint32_t mask;
+
+	mask = CONFIG_UDC_AMBIQ_DEB_ENABLE & 0xFFFF;
+	while (mask) {
+		uint32_t ep = find_lsb_set(mask);
+
+		am_hal_usb_enable_ep_double_buffer(priv->usb_handle, ep, AM_HAL_USB_OUT_DIR, true);
+		mask &= ~(1U << (ep - 1));
+	}
+
+	mask = (CONFIG_UDC_AMBIQ_DEB_ENABLE >> 16) & 0xFFFF;
+	while (mask) {
+		uint32_t ep = find_lsb_set(mask);
+
+		am_hal_usb_enable_ep_double_buffer(priv->usb_handle, ep, AM_HAL_USB_IN_DIR, true);
+		mask &= ~(1U << (ep - 1));
+	}
+}
+#endif
+
 static int udc_ambiq_init(const struct device *dev)
 {
 	struct udc_ambiq_data *priv = udc_get_private(dev);
@@ -599,6 +622,10 @@ static int udc_ambiq_init(const struct device *dev)
 	}
 #endif
 
+#if CONFIG_UDC_AMBIQ_DEB_ENABLE
+	init_double_buffers(priv);
+#endif
+
 	/* Set USB Speed */
 	am_hal_usb_set_dev_speed(priv->usb_handle, priv->usb_speed);
 	/* Enable USB interrupt */