Re: [Xen-devel] [PATCH V2 2/2] xen: arm: implement early prink for 8250 uart

[Chen Baozi <baozich@xxxxxxxxx>]

On Jul 3, 2013, at 7:09 PM, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:

> On Tue, 2013-07-02 at 21:11 +0800, Bamvor Jian Zhang wrote:
>> diff --git a/xen/arch/arm/arm32/debug-8250.inc 
>> b/xen/arch/arm/arm32/debug-8250.inc
>> new file mode 100644
>> index 0000000..c11357d
>> --- /dev/null
>> +++ b/xen/arch/arm/arm32/debug-8250.inc
>> @@ -0,0 +1,48 @@
>> +/*
>> + * xen/arch/arm/arm32/debug-8250.inc
>> + *
>> + * 8250 specific debug code
>> + *
>> + * Bamvor Jian Zhang <bjzhang@xxxxxxxx>
>> + * Copyright (c) 2013 SUSE
>> + *
>> + * This program is free software; you can redistribute it and/or modify
>> + * it under the terms of the GNU General Public License as published by
>> + * the Free Software Foundation; either version 2 of the License, or
>> + * (at your option) any later version.
>> + *
>> + * This program is distributed in the hope that it will be useful,
>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>> + * GNU General Public License for more details.
>> + */
>> +
>> +
>> +#define UART_TX           (0x00<<2)    /* Out: Transmit buffer */
>> +#define UART_LSR          (0x05<<2)    /* In:  Line Status Register */
> 
> Is the shift 2 on Baozi's platform too? Perhaps this could be a #define
> provided in the same style as EARLY_UART_BASE_ADDRESS or via some other
> means?
Yes, mine has the shift 2 too. It is because every register's size is 4-Bytes 
on both of our platforms.

However, it seems this patch doesn't work on OMAP543 (I've modified 
EARLY_UART_BASE_ADDRESS to 0x48020000 which is the correct address). I'm 
looking for the reasons…

> 
> The definitions themselves duplicate those in
> xen/drivers/char/ns16550.c, perhaps we could refactor those into a
> suitable header?
+1

> 
>> +
>> +#define UART_LSR_THRE     0x20         /* Xmit holding register empty */
>> +
>> +/* 8250 UART wait UART to be ready to transmit
>> + * rb: register which contains the UART base address
>> + * rc: scratch register */
>> +.macro early_uart_ready rb, rc
>> +1:
>> +        ldr   \rc, [\rb, #UART_LSR]    /* <- UART_LSR (Line Status 
>> Register) */
>> +        tst   \rc, #UART_LSR_THRE      /* Check BUSY bit */
>> +        beq   1b                       /* Wait for the UART to be ready */
>> +.endm
>> +
>> +/* 8250 UART transmit character
>> + * rb: register which contains the UART base address
>> + * rt: register which contains the character to transmit */
>> +.macro early_uart_transmit rb, rt
>> +        str   \rt, [\rb, #UART_TX]     /* -> UART_TX */
>> +.endm
>> +
>> +/*
>> + * Local variables:
>> + * mode: ASM
>> + * indent-tabs-mode: nil
>> + * End:
>> + */
> 
> 


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