usb: dwc3: Support EBC feature of DWC_usb31

Support configuration and use of bulk endpoints in the so-called EBC
mode described in the DBC_usb31 databook (appendix E)

Added a bit fifo_mode to usb_ep to indicate to the UDC driver that a
specific endpoint is to operate in the EBC (or equivalent) mode when
enabled

Added macros for bits 15 and 14 of DEPCFG parameter 1 to indicate EBC
mode and write back behaviour. These bits will be set to 1 when
configuring an EBC endpoint as described in the programming guide

Signed-off-by: Manan Aurora <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/dwc3/core.h

···
 /* Global HWPARAMS4 Register */
 #define DWC3_GHWPARAMS4_HIBER_SCRATCHBUFS(n)	(((n) & (0x0f << 13)) >> 13)
 #define DWC3_MAX_HIBER_SCRATCHBUFS		15
+#define DWC3_EXT_BUFF_CONTROL		BIT(21)
 
 /* Global HWPARAMS6 Register */
 #define DWC3_GHWPARAMS6_BCSUPPORT		BIT(14)

drivers/usb/dwc3/gadget.c

···
 		params.param1 |= DWC3_DEPCFG_BINTERVAL_M1(bInterval_m1);
 	}
 
+	if (dep->endpoint.fifo_mode) {
+		if (!(dwc->hwparams.hwparams4 & DWC3_EXT_BUFF_CONTROL))
+			return -EINVAL;
+		params.param1 |= DWC3_DEPCFG_EBC_HWO_NOWB | DWC3_DEPCFG_USE_EBC;
+	}
+
 	return dwc3_send_gadget_ep_cmd(dep, DWC3_DEPCMD_SETEPCONFIG, &params);
 }
 

drivers/usb/dwc3/gadget.h

···
 #define DWC3_DEPCFG_XFER_NOT_READY_EN	BIT(10)
 #define DWC3_DEPCFG_FIFO_ERROR_EN	BIT(11)
 #define DWC3_DEPCFG_STREAM_EVENT_EN	BIT(13)
+#define DWC3_DEPCFG_EBC_HWO_NOWB	BIT(14)
+#define DWC3_DEPCFG_USE_EBC		BIT(15)
 #define DWC3_DEPCFG_BINTERVAL_M1(n)	(((n) & 0xff) << 16)
 #define DWC3_DEPCFG_STREAM_CAPABLE	BIT(24)
 #define DWC3_DEPCFG_EP_NUMBER(n)	(((n) & 0x1f) << 25)

include/linux/usb/gadget.h

···
 	unsigned		max_streams:16;
 	unsigned		mult:2;
 	unsigned		maxburst:5;
+	unsigned		fifo_mode:1;
 	u8			address;
 	const struct usb_endpoint_descriptor	*desc;
 	const struct usb_ss_ep_comp_descriptor	*comp_desc;