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ArmPlatformPkg: Fix PL011 Glitches. 

This change corrects 3 problems in the PL011 driver.
1. The TRM states "The UARTLCR_H, UARTIBRD, and UARTFBRD registers must
   not be changed:...when the UART is enabled"
2. The TRM (3.3.8) describes logic requiring the UART to be disabled and
   flushed before adjusting UARTCR.
3. Several redundant calls get made to PL011UartInitializePort, where
   the characteristics do not change, but updating the registers can
   cause glitches in the output stream.

The parameters are compared to the current state and no action taken if
no change of state is required.
Where an update is required, the specified logic is followed, and the
register updates only made when the UART is disabled.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>
Signed-off-by: Evan Lloyd <evan.lloyd@arm.com>
Tested-by: Ryan Harkin <ryan.harkin@linaro.org>
Reviewed-by: Ryan Harkin <ryan.harkin@linaro.org>
This commit is contained in:
Evan Lloyd 2016-06-15 13:52:43 +01:00 committed by Ard Biesheuvel
parent 090916d8bc
commit 16146b984d
1 changed files with 22 additions and 0 deletions
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22
ArmPlatformPkg/Drivers/PL011Uart/PL011Uart.c
View File

@ -32,6 +32,8 @@ STATIC CONST UINT32 mInvalidControlBits = EFI_SERIAL_SOFTWARE_LOOPBACK_ENABLE;
/**
Initialise the serial port to the specified settings.
The serial port is re-configured only if the specified settings
are different from the current settings.
All unspecified settings will be set to the default values.
@param UartBase The base address of the serial device.
@ -191,6 +193,26 @@ PL011UartInitializePort (
Integer = Divisor >> FRACTION_PART_SIZE_IN_BITS;
Fractional = Divisor & FRACTION_PART_MASK;
}
//
// If PL011 is already initialized, check the current settings
// and re-initialize only if the settings are different.
//
if (((MmioRead32 (UartBase + UARTCR) & PL011_UARTCR_UARTEN) != 0) &&
(MmioRead32 (UartBase + UARTLCR_H) == LineControl) &&
(MmioRead32 (UartBase + UARTIBRD) == Integer) &&
(MmioRead32 (UartBase + UARTFBRD) == Fractional)) {
// Nothing to do - already initialized with correct attributes
return RETURN_SUCCESS;
}
// Wait for the end of transmission
while ((MmioRead32 (UartBase + UARTFR) & PL011_UARTFR_TXFE) == 0);
// Disable UART: "The UARTLCR_H, UARTIBRD, and UARTFBRD registers must not be changed
// when the UART is enabled"
MmioWrite32 (UartBase + UARTCR, 0);
// Set Baud Rate Registers
MmioWrite32 (UartBase + UARTIBRD, Integer);
MmioWrite32 (UartBase + UARTFBRD, Fractional);