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

["Bamvor Jian Zhang" <bjzhang@xxxxxxxx>]

Hi, Ian

>>>Wrote "Ian Campbell <Ian.Campbell@xxxxxxxxxx>"> On Tue
> 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?
> 
> The definitions themselves duplicate those in
> xen/drivers/char/ns16550.c, perhaps we could refactor those into a
> suitable header?
yes. it should be. meanwhile considering the shift bit and other things. 
i am not sure how to merge the headers until i got the ns16550 actual used by
arm SOC. 

Bamvor
> 
> > +
> > +#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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