Re: [PATCH] MdeModulePkg/Library/BaseSerialPortLib16550: Ensure FIFO Polled Mode

["Zeng, Star" <star.zeng@intel.com>]

Hi Leo,

I am ok with the code change.
I was just curious about the motivation for the change.
1. No real issue met, but just to follow the doc 8.4.2 ?
2. Real issue met, then what is the issue ?
3. What is the default value of IER for your case ?

If the information are valuable, then they can be added into the commit message for further easy maintenance.

-----Original Message-----
From: Duran, Leo [mailto:leo.duran@amd.com] 
Sent: Wednesday, June 6, 2018 9:05 AM
To: Zeng, Star <star.zeng@intel.com>; Dong, Eric <eric.dong@intel.com>
Cc: edk2-devel@lists.01.org
Subject: RE: [edk2] [PATCH] MdeModulePkg/Library/BaseSerialPortLib16550: Ensure FIFO Polled Mode

Hi Star,

I came across a 16550 model (simulation) which required clearing IER, and it seems that's allowed in the 16650 spec, as noted here:
http://www.ti.com/lit/ds/symlink/pc16550d.pdf

8.4.2 FIFO Polled Mode Operation
With FCR0=1 resetting IER0, IER1, IER2, IER3 or all to zero puts the UART in the FIFO Polled Mode of operation.

Thanks,
Leo.

> -----Original Message-----
> From: Zeng, Star [mailto:star.zeng@intel.com]
> Sent: Tuesday, June 05, 2018 7:43 PM
> To: Duran, Leo <leo.duran@amd.com>; Dong, Eric <eric.dong@intel.com>
> Cc: edk2-devel@lists.01.org; Zeng, Star <star.zeng@intel.com>
> Subject: RE: [edk2] [PATCH] MdeModulePkg/Library/BaseSerialPortLib16550:
> Ensure FIFO Polled Mode
> 
> It will be better to have the information that may could be added into 
> the commit message.
> 
> 1. Did you meet real issue without this patch?
> 2. what is the default value of IER in your case?
> 
> 
> Thanks,
> Star
> -----Original Message-----
> From: Duran, Leo [mailto:leo.duran@amd.com]
> Sent: Wednesday, June 6, 2018 5:21 AM
> To: Zeng, Star <star.zeng@intel.com>; Dong, Eric <eric.dong@intel.com>
> Cc: edk2-devel@lists.01.org
> Subject: RE: [edk2] [PATCH] MdeModulePkg/Library/BaseSerialPortLib16550:
> Ensure FIFO Polled Mode
> 
> Any updates on this patch?
> 
> Do you require to know my "default value of IER"?
> 
> Thanks,
> Leo.
> 
> -----Original Message-----
> From: edk2-devel <edk2-devel-bounces@lists.01.org> On Behalf Of Duran, 
> Leo
> Sent: Friday, May 25, 2018 8:38 AM
> To: Zeng, Star <star.zeng@intel.com>; edk2-devel@lists.01.org
> Cc: Dong, Eric <eric.dong@intel.com>; Zeng, Star <star.zeng@intel.com>
> Subject: Re: [edk2] [PATCH] MdeModulePkg/Library/BaseSerialPortLib16550:
> Ensure FIFO Polled Mode
> 
> Don''t have access to test platform at this time.
> But will report IER value if I,m able to.
> 
> Leo
> 
> Get Outlook for iOS<https://aka.ms/o0ukef> 
> ________________________________
> From: Zeng, Star <star.zeng@intel.com>
> Sent: Friday, May 25, 2018 6:13:16 AM
> To: Duran, Leo; edk2-devel@lists.01.org
> Cc: Dong, Eric; Zeng, Star
> Subject: RE: [edk2] [PATCH] MdeModulePkg/Library/BaseSerialPortLib16550:
> Ensure FIFO Polled Mode
> 
> Reviewed-by: Star Zeng <star.zeng@intel.com>
> 
> Just a little curious about
> 1. Did you meet real issue without this patch?
> 2. what is the default value of IER in your case?
> 
> 
> Thanks,
> Star
> -----Original Message-----
> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of 
> Leo Duran
> Sent: Friday, May 25, 2018 3:08 AM
> To: edk2-devel@lists.01.org
> Cc: Dong, Eric <eric.dong@intel.com>; Zeng, Star <star.zeng@intel.com>
> Subject: [edk2] [PATCH] MdeModulePkg/Library/BaseSerialPortLib16550:
> Ensure FIFO Polled Mode
> 
> Put the UART in FIFO Polled Mode by clearing IER after setting FCR.
> Also, add comments to show DLAB state for registers 0 and 1.
> 
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Leo Duran <leo.duran@amd.com>
> Cc: Star Zeng <star.zeng@intel.com>
> CC: Eric Dong <eric.dong@intel.com>
> ---
>  .../BaseSerialPortLib16550/BaseSerialPortLib16550.c      | 16 ++++++++++++--
> --
>  1 file changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git
> a/MdeModulePkg/Library/BaseSerialPortLib16550/BaseSerialPortLib16550.c
> b/MdeModulePkg/Library/BaseSerialPortLib16550/BaseSerialPortLib16550.c
> index 0ccac96..6532c4d 100644
> ---
> a/MdeModulePkg/Library/BaseSerialPortLib16550/BaseSerialPortLib16550.c
> +++
> b/MdeModulePkg/Library/BaseSerialPortLib16550/BaseSerialPortLib16550
> +++ .c
> @@ -3,6 +3,8 @@
> 
>    (C) Copyright 2014 Hewlett-Packard Development Company, L.P.<BR>
>    Copyright (c) 2006 - 2016, Intel Corporation. All rights 
> reserved.<BR>
> +  Copyright (c) 2018, AMD Incorporated. All rights reserved.<BR>
> +
>    This program and the accompanying materials
>    are licensed and made available under the terms and conditions of 
> the BSD License
>    which accompanies this distribution.  The full text of the license 
> may be found at @@ -30,10 +32,11 @@  //  // 16550 UART register 
> offsets and bitfields  //
> -#define R_UART_RXBUF          0
> -#define R_UART_TXBUF          0
> -#define R_UART_BAUD_LOW       0
> -#define R_UART_BAUD_HIGH      1
> +#define R_UART_RXBUF          0   // LCR_DLAB = 0
> +#define R_UART_TXBUF          0   // LCR_DLAB = 0
> +#define R_UART_BAUD_LOW       0   // LCR_DLAB = 1
> +#define R_UART_BAUD_HIGH      1   // LCR_DLAB = 1
> +#define R_UART_IER            1   // LCR_DLAB = 0
>  #define R_UART_FCR            2
>  #define   B_UART_FCR_FIFOE    BIT0
>  #define   B_UART_FCR_FIFO64   BIT5
> @@ -554,6 +557,11 @@ SerialPortInitialize (
>    SerialPortWriteRegister (SerialRegisterBase, R_UART_FCR,
> (UINT8)(PcdGet8 (PcdSerialFifoControl) & (B_UART_FCR_FIFOE | 
> B_UART_FCR_FIFO64)));
> 
>    //
> +  // Set FIFO Polled Mode by clearing IER after setting FCR  // 
> + SerialPortWriteRegister (SerialRegisterBase, R_UART_IER, 0x00);
> +
> +  //
>    // Put Modem Control Register(MCR) into its reset state of 0x00.
>    //
>    SerialPortWriteRegister (SerialRegisterBase, R_UART_MCR, 0x00);
> --
> 2.7.4
> 
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