diff options
Diffstat (limited to 'MdeModulePkg')
| -rw-r--r-- | MdeModulePkg/Bus/Pci/PciSioSerialDxe/SerialIo.c | 91 |
1 files changed, 90 insertions, 1 deletions
diff --git a/MdeModulePkg/Bus/Pci/PciSioSerialDxe/SerialIo.c b/MdeModulePkg/Bus/Pci/PciSioSerialDxe/SerialIo.c index 8377ffa13c..56c5faf5db 100644 --- a/MdeModulePkg/Bus/Pci/PciSioSerialDxe/SerialIo.c +++ b/MdeModulePkg/Bus/Pci/PciSioSerialDxe/SerialIo.c @@ -1,7 +1,7 @@ /** @file
SerialIo implementation for PCI or SIO UARTs.
-Copyright (c) 2006 - 2018, Intel Corporation. All rights reserved.<BR>
+Copyright (c) 2006 - 2020, Intel Corporation. All rights reserved.<BR>
SPDX-License-Identifier: BSD-2-Clause-Patent
**/
@@ -436,6 +436,68 @@ SerialReceiveTransmit ( return EFI_SUCCESS;
}
+/**
+ Flush the serial hardware transmit FIFO, holding register, and shift register.
+
+ @param SerialDevice The device to flush.
+
+ @retval EFI_SUCCESS The transmit FIFO is completely flushed.
+ @retval EFI_TIMEOUT A timeout occured waiting for the transmit FIFO to flush.
+**/
+EFI_STATUS
+SerialFlushTransmitFifo (
+ SERIAL_DEV *SerialDevice
+ )
+{
+ SERIAL_PORT_LSR Lsr;
+ UINTN Timeout;
+ UINTN Elapsed;
+
+ //
+ // If this is the first time the UART is being configured, then the current
+ // UART settings are not known, so compute a timeout to wait for the Tx FIFO
+ // assuming the worst case current settings.
+ //
+ // Timeout = (Max Bits per Char) * (Max Pending Chars) / (Slowest Baud Rate)
+ // Max Bits per Char = Start bit + 8 data bits + parity + 2 stop bits = 12
+ // Max Pending Chars = Largest Tx FIFO + hold + shift = 64 + 1 + 1 = 66
+ // Slowest Reasonable Baud Rate = 300 baud
+ // Timeout = 12 * 66 / 300 = 2.64 seconds = 2,640,000 uS
+ //
+ Timeout = 2640000;
+
+ //
+ // Use the largest of the computed timeout, the default timeout, and the
+ // currently set timeout.
+ //
+ Timeout = MAX (Timeout, SERIAL_PORT_DEFAULT_TIMEOUT);
+ Timeout = MAX (Timeout, SerialDevice->SerialMode.Timeout);
+
+ //
+ // Wait for the shortest time possible for the serial port to be ready making
+ // sure the transmit FIFO, holding register, and shift register are all
+ // empty. The actual wait time is expected to be very small because the
+ // number characters currently in the FIFO should be small when a
+ // configuration change is requested.
+ //
+ // NOTE: Do not use any DEBUG() or REPORT_STATUS_CODE() or any other calls
+ // in the rest of this function that may send additional characters to this
+ // UART device invalidating the flush operation.
+ //
+ Elapsed = 0;
+ Lsr.Data = READ_LSR (SerialDevice);
+ while (Lsr.Bits.Temt == 0 || Lsr.Bits.Thre == 0) {
+ if (Elapsed >= Timeout) {
+ return EFI_TIMEOUT;
+ }
+ gBS->Stall (TIMEOUT_STALL_INTERVAL);
+ Elapsed += TIMEOUT_STALL_INTERVAL;
+ Lsr.Data = READ_LSR (SerialDevice);
+ }
+
+ return EFI_SUCCESS;
+}
+
//
// Interface Functions
//
@@ -477,6 +539,15 @@ SerialReset ( Tpl = gBS->RaiseTPL (TPL_NOTIFY);
//
+ // Wait for all data to be transmitted before changing the UART configuration.
+ //
+ // NOTE: Do not use any DEBUG() or REPORT_STATUS_CODE() or any other calls
+ // that may send additional characters to this UART device until the UART
+ // configuration change is complete.
+ //
+ SerialFlushTransmitFifo (SerialDevice);
+
+ //
// Make sure DLAB is 0.
//
Lcr.Data = READ_LCR (SerialDevice);
@@ -655,6 +726,15 @@ SerialSetAttributes ( Tpl = gBS->RaiseTPL (TPL_NOTIFY);
//
+ // Wait for all data to be transmitted before changing the UART configuration.
+ //
+ // NOTE: Do not use any DEBUG() or REPORT_STATUS_CODE() or any other calls
+ // that may send additional characters to this UART device until the UART
+ // configuration change is complete.
+ //
+ SerialFlushTransmitFifo (SerialDevice);
+
+ //
// Put serial port on Divisor Latch Mode
//
Lcr.Data = READ_LCR (SerialDevice);
@@ -826,6 +906,15 @@ SerialSetControl ( Tpl = gBS->RaiseTPL (TPL_NOTIFY);
+ //
+ // Wait for all data to be transmitted before changing the UART configuration.
+ //
+ // NOTE: Do not use any DEBUG() or REPORT_STATUS_CODE() or any other calls
+ // that may send additional characters to this UART device until the UART
+ // configuration change is complete.
+ //
+ SerialFlushTransmitFifo (SerialDevice);
+
Mcr.Data = READ_MCR (SerialDevice);
Mcr.Bits.DtrC = 0;
Mcr.Bits.Rts = 0;
|