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ArmPlatformPkg: Tidy PL011 UART driver

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This cosmetic change only tidies things up in preparation for actual
updates. (This reflects responses to a previously submitted patch,
which has been split into several discrete changes.)
There are no functional changes in this commit.
Changes comprise:
  Minor corrections to comment typos.
  Minor formatting mods.
  Expansion of function comments.
  Remove OUT from UartBase parameter.
  Addition of #define for "magic mumbers".

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Evan Lloyd <evan.lloyd@arm.com>
Reviewed-by: Ryan Harkin <ryan.harkin@linaro.org>
This commit is contained in:
Evan Lloyd
2016-06-15 13:52:38 +01:00
committed by Ard Biesheuvel
parent 8f88f023fc
commit 9f08a052a3
3 changed files with 182 additions and 105 deletions
Download Patch File Download Diff File Expand all files Collapse all files

101
ArmPlatformPkg/Drivers/PL011Uart/PL011Uart.c
View File

@@ -2,7 +2,7 @@
Serial I/O Port library functions with no library constructor/destructor Serial I/O Port library functions with no library constructor/destructor
Copyright (c) 2008 - 2010, Apple Inc. All rights reserved.<BR> Copyright (c) 2008 - 2010, Apple Inc. All rights reserved.<BR>
Copyright (c) 2011 - 2014, ARM Ltd. All rights reserved.<BR> Copyright (c) 2011 - 2016, ARM Ltd. All rights reserved.<BR>
This program and the accompanying materials This program and the accompanying materials
are licensed and made available under the terms and conditions of the BSD License are licensed and made available under the terms and conditions of the BSD License
@@ -20,24 +20,49 @@
#include <Drivers/PL011Uart.h> #include <Drivers/PL011Uart.h>
#define FRACTION_PART_SIZE_IN_BITS 6
#define FRACTION_PART_MASK ((1 << FRACTION_PART_SIZE_IN_BITS) - 1)
// //
// EFI_SERIAL_SOFTWARE_LOOPBACK_ENABLE is the only // EFI_SERIAL_SOFTWARE_LOOPBACK_ENABLE is the only
// control bit that is not supported. // control bit that is not supported.
// //
STATIC CONST UINT32 mInvalidControlBits = EFI_SERIAL_SOFTWARE_LOOPBACK_ENABLE; STATIC CONST UINT32 mInvalidControlBits = EFI_SERIAL_SOFTWARE_LOOPBACK_ENABLE;
/* /**
Initialise the serial port to the specified settings. Initialise the serial port to the specified settings.
All unspecified settings will be set to the default values. All unspecified settings will be set to the default values.
@return Always return EFI_SUCCESS or EFI_INVALID_PARAMETER. @param UartBase The base address of the serial device.
@param BaudRate The baud rate of the serial device. If the
baud rate is not supported, the speed will be
reduced to the nearest supported one and the
variable's value will be updated accordingly.
@param ReceiveFifoDepth The number of characters the device will
buffer on input. Value of 0 will use the
device's default FIFO depth.
@param Parity If applicable, this is the EFI_PARITY_TYPE
that is computed or checked as each character
is transmitted or received. If the device
does not support parity, the value is the
default parity value.
@param DataBits The number of data bits in each character.
@param StopBits If applicable, the EFI_STOP_BITS_TYPE number
of stop bits per character.
If the device does not support stop bits, the
value is the default stop bit value.
@retval RETURN_SUCCESS All attributes were set correctly on the
serial device.
@retval RETURN_INVALID_PARAMETER One or more of the attributes has an
unsupported value.
**/ **/
RETURN_STATUS RETURN_STATUS
EFIAPI EFIAPI
PL011UartInitializePort ( PL011UartInitializePort (
IN OUT UINTN UartBase, IN UINTN UartBase,
IN OUT UINT64 *BaudRate, IN OUT UINT64 *BaudRate,
IN OUT UINT32 *ReceiveFifoDepth, IN OUT UINT32 *ReceiveFifoDepth,
IN OUT EFI_PARITY_TYPE *Parity, IN OUT EFI_PARITY_TYPE *Parity,
@@ -51,9 +76,10 @@ PL011UartInitializePort (
LineControl = 0; LineControl = 0;
// The PL011 supports a buffer of 1, 16 or 32 chars. Therefore we can accept // The PL011 supports a buffer of 1, 16 or 32 chars. Therefore we can accept
// 1 char buffer as the minimum fifo size. Because everything can be rounded down, // 1 char buffer as the minimum FIFO size. Because everything can be rounded
// there is no maximum fifo size. // down, there is no maximum FIFO size.
if ((*ReceiveFifoDepth == 0) || (*ReceiveFifoDepth >= 32)) { if ((*ReceiveFifoDepth == 0) || (*ReceiveFifoDepth >= 32)) {
// Enable FIFO
LineControl |= PL011_UARTLCR_H_FEN; LineControl |= PL011_UARTLCR_H_FEN;
if (PL011_UARTPID2_VER (MmioRead32 (UartBase + UARTPID2)) > PL011_VER_R1P4) if (PL011_UARTPID2_VER (MmioRead32 (UartBase + UARTPID2)) > PL011_VER_R1P4)
*ReceiveFifoDepth = 32; *ReceiveFifoDepth = 32;
@@ -61,7 +87,7 @@ PL011UartInitializePort (
*ReceiveFifoDepth = 16; *ReceiveFifoDepth = 16;
} else { } else {
ASSERT (*ReceiveFifoDepth < 32); ASSERT (*ReceiveFifoDepth < 32);
// Nothing else to do. 1 byte fifo is default. // Nothing else to do. 1 byte FIFO is default.
*ReceiveFifoDepth = 1; *ReceiveFifoDepth = 1;
} }
@@ -81,7 +107,9 @@ PL011UartInitializePort (
LineControl |= PL011_UARTLCR_H_PEN; LineControl |= PL011_UARTLCR_H_PEN;
break; break;
case MarkParity: case MarkParity:
LineControl |= (PL011_UARTLCR_H_PEN | PL011_UARTLCR_H_SPS | PL011_UARTLCR_H_EPS); LineControl |= ( PL011_UARTLCR_H_PEN \
| PL011_UARTLCR_H_SPS \
| PL011_UARTLCR_H_EPS);
break; break;
case SpaceParity: case SpaceParity:
LineControl |= (PL011_UARTLCR_H_PEN | PL011_UARTLCR_H_SPS); LineControl |= (PL011_UARTLCR_H_PEN | PL011_UARTLCR_H_SPS);
@@ -125,7 +153,7 @@ PL011UartInitializePort (
LineControl |= PL011_UARTLCR_H_STP2; LineControl |= PL011_UARTLCR_H_STP2;
break; break;
case OneFiveStopBits: case OneFiveStopBits:
// Only 1 or 2 stops bits are supported // Only 1 or 2 stop bits are supported
default: default:
return RETURN_INVALID_PARAMETER; return RETURN_INVALID_PARAMETER;
} }
@@ -139,7 +167,7 @@ PL011UartInitializePort (
// Baud Rate // Baud Rate
// //
// If PL011 Integral value has been defined then always ignore the BAUD rate // If PL011 Integer value has been defined then always ignore the BAUD rate
if (PcdGet32 (PL011UartInteger) != 0) { if (PcdGet32 (PL011UartInteger) != 0) {
MmioWrite32 (UartBase + UARTIBRD, PcdGet32 (PL011UartInteger)); MmioWrite32 (UartBase + UARTIBRD, PcdGet32 (PL011UartInteger));
MmioWrite32 (UartBase + UARTFBRD, PcdGet32 (PL011UartFractional)); MmioWrite32 (UartBase + UARTFBRD, PcdGet32 (PL011UartFractional));
@@ -151,8 +179,8 @@ PL011UartInitializePort (
} }
Divisor = (PcdGet32 (PL011UartClkInHz) * 4) / *BaudRate; Divisor = (PcdGet32 (PL011UartClkInHz) * 4) / *BaudRate;
MmioWrite32 (UartBase + UARTIBRD, Divisor >> 6); MmioWrite32 (UartBase + UARTIBRD, Divisor >> FRACTION_PART_SIZE_IN_BITS);
MmioWrite32 (UartBase + UARTFBRD, Divisor & 0x3F); MmioWrite32 (UartBase + UARTFBRD, Divisor & FRACTION_PART_MASK);
} }
// No parity, 1 stop, no fifo, 8 data bits // No parity, 1 stop, no fifo, 8 data bits
@@ -161,8 +189,9 @@ PL011UartInitializePort (
// Clear any pending errors // Clear any pending errors
MmioWrite32 (UartBase + UARTECR, 0); MmioWrite32 (UartBase + UARTECR, 0);
// Enable tx, rx, and uart overall // Enable Tx, Rx, and UART overall
MmioWrite32 (UartBase + UARTCR, PL011_UARTCR_RXE | PL011_UARTCR_TXE | PL011_UARTCR_UARTEN); MmioWrite32 (UartBase + UARTCR,
PL011_UARTCR_RXE | PL011_UARTCR_TXE | PL011_UARTCR_UARTEN);
return RETURN_SUCCESS; return RETURN_SUCCESS;
} }
@@ -190,8 +219,8 @@ PL011UartInitializePort (
disable the hardware flow control based on CTS (Clear disable the hardware flow control based on CTS (Clear
To Send) and RTS (Ready To Send) control signals. To Send) and RTS (Ready To Send) control signals.
@retval RETURN_SUCCESS The new control bits were set on the serial device. @retval RETURN_SUCCESS The new control bits were set on the device.
@retval RETURN_UNSUPPORTED The serial device does not support this operation. @retval RETURN_UNSUPPORTED The device does not support this operation.
**/ **/
RETURN_STATUS RETURN_STATUS
@@ -245,24 +274,28 @@ PL011UartSetControl (
@param[in] UartBase UART registers base address @param[in] UartBase UART registers base address
@param[out] Control Status of the control bits on a serial device : @param[out] Control Status of the control bits on a serial device :
. EFI_SERIAL_DATA_CLEAR_TO_SEND, EFI_SERIAL_DATA_SET_READY, . EFI_SERIAL_DATA_CLEAR_TO_SEND,
EFI_SERIAL_RING_INDICATE, EFI_SERIAL_CARRIER_DETECT, EFI_SERIAL_DATA_SET_READY,
EFI_SERIAL_REQUEST_TO_SEND, EFI_SERIAL_DATA_TERMINAL_READY EFI_SERIAL_RING_INDICATE,
are all related to the DTE (Data Terminal Equipment) and EFI_SERIAL_CARRIER_DETECT,
DCE (Data Communication Equipment) modes of operation of EFI_SERIAL_REQUEST_TO_SEND,
the serial device. EFI_SERIAL_DATA_TERMINAL_READY
. EFI_SERIAL_INPUT_BUFFER_EMPTY : equal to one if the receive are all related to the DTE (Data Terminal Equipment)
buffer is empty, 0 otherwise. and DCE (Data Communication Equipment) modes of
. EFI_SERIAL_OUTPUT_BUFFER_EMPTY : equal to one if the transmit operation of the serial device.
buffer is empty, 0 otherwise. . EFI_SERIAL_INPUT_BUFFER_EMPTY : equal to one if the
. EFI_SERIAL_HARDWARE_LOOPBACK_ENABLE : equal to one if the receive buffer is empty, 0 otherwise.
hardware loopback is enabled (the ouput feeds the receive . EFI_SERIAL_OUTPUT_BUFFER_EMPTY : equal to one if the
buffer), 0 otherwise. transmit buffer is empty, 0 otherwise.
. EFI_SERIAL_SOFTWARE_LOOPBACK_ENABLE : equal to one if a . EFI_SERIAL_HARDWARE_LOOPBACK_ENABLE : equal to one if
loopback is accomplished by software, 0 otherwise. the hardware loopback is enabled (the ouput feeds the
. EFI_SERIAL_HARDWARE_FLOW_CONTROL_ENABLE : equal to one if the receive buffer), 0 otherwise.
hardware flow control based on CTS (Clear To Send) and RTS . EFI_SERIAL_SOFTWARE_LOOPBACK_ENABLE : equal to one if
(Ready To Send) control signals is enabled, 0 otherwise. a loopback is accomplished by software, 0 otherwise.
. EFI_SERIAL_HARDWARE_FLOW_CONTROL_ENABLE : equal to
one if the hardware flow control based on CTS (Clear
To Send) and RTS (Ready To Send) control signals is
enabled, 0 otherwise.
@retval RETURN_SUCCESS The control bits were read from the serial device. @retval RETURN_SUCCESS The control bits were read from the serial device.

76
ArmPlatformPkg/Include/Drivers/PL011Uart.h
View File

@@ -1,6 +1,6 @@
/** @file /** @file
* *
* Copyright (c) 2011-2014, ARM Limited. All rights reserved. * Copyright (c) 2011-2016, ARM Limited. All rights reserved.
* *
* This program and the accompanying materials * This program and the accompanying materials
* are licensed and made available under the terms and conditions of the BSD License * are licensed and made available under the terms and conditions of the BSD License
@@ -91,15 +91,38 @@
/* /*
Programmed hardware of Serial port. Initialise the serial port to the specified settings.
All unspecified settings will be set to the default values.
@return Always return EFI_UNSUPPORTED. @param UartBase The base address of the serial device.
@param BaudRate The baud rate of the serial device. If the
baud rate is not supported, the speed will be
reduced to the nearest supported one and the
variable's value will be updated accordingly.
@param ReceiveFifoDepth The number of characters the device will
buffer on input. Value of 0 will use the
device's default FIFO depth.
@param Parity If applicable, this is the EFI_PARITY_TYPE
that is computed or checked as each character
is transmitted or received. If the device
does not support parity, the value is the
default parity value.
@param DataBits The number of data bits in each character.
@param StopBits If applicable, the EFI_STOP_BITS_TYPE number
of stop bits per character.
If the device does not support stop bits, the
value is the default stop bit value.
@retval RETURN_SUCCESS All attributes were set correctly on the
serial device.
@retval RETURN_INVALID_PARAMETER One or more of the attributes has an
unsupported value.
**/ **/
RETURN_STATUS RETURN_STATUS
EFIAPI EFIAPI
PL011UartInitializePort ( PL011UartInitializePort (
IN OUT UINTN UartBase, IN UINTN UartBase,
IN OUT UINT64 *BaudRate, IN OUT UINT64 *BaudRate,
IN OUT UINT32 *ReceiveFifoDepth, IN OUT UINT32 *ReceiveFifoDepth,
IN OUT EFI_PARITY_TYPE *Parity, IN OUT EFI_PARITY_TYPE *Parity,
@@ -130,8 +153,8 @@ PL011UartInitializePort (
disable the hardware flow control based on CTS (Clear disable the hardware flow control based on CTS (Clear
To Send) and RTS (Ready To Send) control signals. To Send) and RTS (Ready To Send) control signals.
@retval RETURN_SUCCESS The new control bits were set on the serial device. @retval RETURN_SUCCESS The new control bits were set on the device.
@retval RETURN_UNSUPPORTED The serial device does not support this operation. @retval RETURN_UNSUPPORTED The device does not support this operation.
**/ **/
RETURN_STATUS RETURN_STATUS
@@ -148,25 +171,28 @@ PL011UartSetControl (
@param[in] UartBase UART registers base address @param[in] UartBase UART registers base address
@param[out] Control Status of the control bits on a serial device : @param[out] Control Status of the control bits on a serial device :
. EFI_SERIAL_DATA_CLEAR_TO_SEND, EFI_SERIAL_DATA_SET_READY, . EFI_SERIAL_DATA_CLEAR_TO_SEND,
EFI_SERIAL_RING_INDICATE, EFI_SERIAL_CARRIER_DETECT, EFI_SERIAL_DATA_SET_READY,
EFI_SERIAL_REQUEST_TO_SEND, EFI_SERIAL_DATA_TERMINAL_READY EFI_SERIAL_RING_INDICATE,
are all related to the DTE (Data Terminal Equipment) and EFI_SERIAL_CARRIER_DETECT,
DCE (Data Communication Equipment) modes of operation of EFI_SERIAL_REQUEST_TO_SEND,
the serial device. EFI_SERIAL_DATA_TERMINAL_READY
. EFI_SERIAL_INPUT_BUFFER_EMPTY : equal to one if the receive are all related to the DTE (Data Terminal Equipment)
buffer is empty, 0 otherwise. and DCE (Data Communication Equipment) modes of
. EFI_SERIAL_OUTPUT_BUFFER_EMPTY : equal to one if the transmit operation of the serial device.
buffer is empty, 0 otherwise. . EFI_SERIAL_INPUT_BUFFER_EMPTY : equal to one if the
. EFI_SERIAL_HARDWARE_LOOPBACK_ENABLE : equal to one if the receive buffer is empty, 0 otherwise.
hardware loopback is enabled (the ouput feeds the receive . EFI_SERIAL_OUTPUT_BUFFER_EMPTY : equal to one if the
buffer), 0 otherwise. transmit buffer is empty, 0 otherwise.
. EFI_SERIAL_SOFTWARE_LOOPBACK_ENABLE : equal to one if a . EFI_SERIAL_HARDWARE_LOOPBACK_ENABLE : equal to one if
loopback is accomplished by software, 0 otherwise. the hardware loopback is enabled (the ouput feeds the
. EFI_SERIAL_HARDWARE_FLOW_CONTROL_ENABLE : equal to one if the receive buffer), 0 otherwise.
hardware flow control based on CTS (Clear To Send) and RTS . EFI_SERIAL_SOFTWARE_LOOPBACK_ENABLE : equal to one if
(Ready To Send) control signals is enabled, 0 otherwise. a loopback is accomplished by software, 0 otherwise.
. EFI_SERIAL_HARDWARE_FLOW_CONTROL_ENABLE : equal to
one if the hardware flow control based on CTS (Clear
To Send) and RTS (Ready To Send) control signals is
enabled, 0 otherwise.
@retval RETURN_SUCCESS The control bits were read from the serial device. @retval RETURN_SUCCESS The control bits were read from the serial device.

100
ArmPlatformPkg/Library/PL011SerialPortLib/PL011SerialPortLib.c
View File

@@ -2,7 +2,7 @@
Serial I/O Port library functions with no library constructor/destructor Serial I/O Port library functions with no library constructor/destructor
Copyright (c) 2008 - 2010, Apple Inc. All rights reserved.<BR> Copyright (c) 2008 - 2010, Apple Inc. All rights reserved.<BR>
Copyright (c) 2012 - 2014, ARM Ltd. All rights reserved.<BR> Copyright (c) 2012 - 2016, ARM Ltd. All rights reserved.<BR>
Copyright (c) 2015, Intel Corporation. All rights reserved.<BR> Copyright (c) 2015, Intel Corporation. All rights reserved.<BR>
This program and the accompanying materials This program and the accompanying materials
@@ -44,14 +44,19 @@ SerialPortInitialize (
EFI_STOP_BITS_TYPE StopBits; EFI_STOP_BITS_TYPE StopBits;
BaudRate = (UINTN)PcdGet64 (PcdUartDefaultBaudRate); BaudRate = (UINTN)PcdGet64 (PcdUartDefaultBaudRate);
ReceiveFifoDepth = 0; // Use the default value for Fifo depth ReceiveFifoDepth = 0; // Use default FIFO depth
Parity = (EFI_PARITY_TYPE)PcdGet8 (PcdUartDefaultParity); Parity = (EFI_PARITY_TYPE)PcdGet8 (PcdUartDefaultParity);
DataBits = PcdGet8 (PcdUartDefaultDataBits); DataBits = PcdGet8 (PcdUartDefaultDataBits);
StopBits = (EFI_STOP_BITS_TYPE) PcdGet8 (PcdUartDefaultStopBits); StopBits = (EFI_STOP_BITS_TYPE) PcdGet8 (PcdUartDefaultStopBits);
return PL011UartInitializePort ( return PL011UartInitializePort (
(UINTN)PcdGet64 (PcdSerialRegisterBase), (UINTN)PcdGet64 (PcdSerialRegisterBase),
&BaudRate, &ReceiveFifoDepth, &Parity, &DataBits, &StopBits); &BaudRate,
&ReceiveFifoDepth,
&Parity,
&DataBits,
&StopBits
);
} }
/** /**
@@ -113,24 +118,32 @@ SerialPortPoll (
/** /**
Set new attributes to PL011. Set new attributes to PL011.
@param BaudRate The baud rate of the serial device. If the baud rate is not supported, @param BaudRate The baud rate of the serial device. If the
the speed will be reduced down to the nearest supported one and the baud rate is not supported, the speed will
variable's value will be updated accordingly. be reduced down to the nearest supported one
@param ReceiveFifoDepth The number of characters the device will buffer on input. If the specified and the variable's value will be updated
value is not supported, the variable's value will be reduced down to the accordingly.
nearest supported one. @param ReceiveFifoDepth The number of characters the device will
@param Timeout If applicable, the number of microseconds the device will wait buffer on input. If the specified value is
before timing out a Read or a Write operation. not supported, the variable's value will
@param Parity If applicable, this is the EFI_PARITY_TYPE that is computed or checked be reduced down to the nearest supported one.
as each character is transmitted or received. If the device does not @param Timeout If applicable, the number of microseconds the
support parity, the value is the default parity value. device will wait before timing out a Read or
a Write operation.
@param Parity If applicable, this is the EFI_PARITY_TYPE
that is computed or checked as each character
is transmitted or received. If the device
does not support parity, the value is the
default parity value.
@param DataBits The number of data bits in each character @param DataBits The number of data bits in each character
@param StopBits If applicable, the EFI_STOP_BITS_TYPE number of stop bits per character. @param StopBits If applicable, the EFI_STOP_BITS_TYPE number
If the device does not support stop bits, the value is the default stop of stop bits per character. If the device
bit value. does not support stop bits, the value is the
default stop bit value.
@retval EFI_SUCCESS All attributes were set correctly on the serial device. @retval EFI_SUCCESS All attributes were set correctly.
@retval EFI_INVALID_PARAMETERS One or more of the attributes has an unsupported value. @retval EFI_INVALID_PARAMETERS One or more attributes has an unsupported
value.
**/ **/
RETURN_STATUS RETURN_STATUS
@@ -150,7 +163,8 @@ SerialPortSetAttributes (
ReceiveFifoDepth, ReceiveFifoDepth,
Parity, Parity,
DataBits, DataBits,
StopBits); StopBits
);
} }
/** /**
@@ -175,8 +189,8 @@ SerialPortSetAttributes (
disable the hardware flow control based on CTS (Clear disable the hardware flow control based on CTS (Clear
To Send) and RTS (Ready To Send) control signals. To Send) and RTS (Ready To Send) control signals.
@retval RETURN_SUCCESS The new control bits were set on the serial device. @retval RETURN_SUCCESS The new control bits were set on the device.
@retval RETURN_UNSUPPORTED The serial device does not support this operation. @retval RETURN_UNSUPPORTED The device does not support this operation.
**/ **/
RETURN_STATUS RETURN_STATUS
@@ -194,26 +208,30 @@ SerialPortSetControl (
@param[out] Control Status of the control bits on a serial device : @param[out] Control Status of the control bits on a serial device :
. EFI_SERIAL_DATA_CLEAR_TO_SEND, EFI_SERIAL_DATA_SET_READY, . EFI_SERIAL_DATA_CLEAR_TO_SEND,
EFI_SERIAL_RING_INDICATE, EFI_SERIAL_CARRIER_DETECT, EFI_SERIAL_DATA_SET_READY,
EFI_SERIAL_REQUEST_TO_SEND, EFI_SERIAL_DATA_TERMINAL_READY EFI_SERIAL_RING_INDICATE,
are all related to the DTE (Data Terminal Equipment) and EFI_SERIAL_CARRIER_DETECT,
DCE (Data Communication Equipment) modes of operation of EFI_SERIAL_REQUEST_TO_SEND,
the serial device. EFI_SERIAL_DATA_TERMINAL_READY
. EFI_SERIAL_INPUT_BUFFER_EMPTY : equal to one if the receive are all related to the DTE (Data Terminal Equipment)
buffer is empty, 0 otherwise. and DCE (Data Communication Equipment) modes of
. EFI_SERIAL_OUTPUT_BUFFER_EMPTY : equal to one if the transmit operation of the serial device.
buffer is empty, 0 otherwise. . EFI_SERIAL_INPUT_BUFFER_EMPTY : equal to one if the
. EFI_SERIAL_HARDWARE_LOOPBACK_ENABLE : equal to one if the receive buffer is empty, 0 otherwise.
hardware loopback is enabled (the output feeds the receive . EFI_SERIAL_OUTPUT_BUFFER_EMPTY : equal to one if the
buffer), 0 otherwise. transmit buffer is empty, 0 otherwise.
. EFI_SERIAL_SOFTWARE_LOOPBACK_ENABLE : equal to one if a . EFI_SERIAL_HARDWARE_LOOPBACK_ENABLE : equal to one if
loopback is accomplished by software, 0 otherwise. the hardware loopback is enabled (the output feeds
. EFI_SERIAL_HARDWARE_FLOW_CONTROL_ENABLE : equal to one if the the receive buffer), 0 otherwise.
hardware flow control based on CTS (Clear To Send) and RTS . EFI_SERIAL_SOFTWARE_LOOPBACK_ENABLE : equal to one
(Ready To Send) control signals is enabled, 0 otherwise. if a loopback is accomplished by software, else 0.
. EFI_SERIAL_HARDWARE_FLOW_CONTROL_ENABLE : equal to
one if the hardware flow control based on CTS (Clear
To Send) and RTS (Ready To Send) control signals is
enabled, 0 otherwise.
@retval RETURN_SUCCESS The control bits were read from the serial device. @retval RETURN_SUCCESS The control bits were read from the device.
**/ **/
RETURN_STATUS RETURN_STATUS