RE: [XEN RFC PATCH 02/40] xen/arm: Print a 64-bit number in hex from early uart

[Wei Chen <Wei.Chen@xxxxxxx>]

Hi Julien,

> -----Original Message-----
> From: Julien Grall <julien@xxxxxxx>
> Sent: 2021年8月19日 21:05
> To: Wei Chen <Wei.Chen@xxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx;
> sstabellini@xxxxxxxxxx; jbeulich@xxxxxxxx
> Cc: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>
> Subject: Re: [XEN RFC PATCH 02/40] xen/arm: Print a 64-bit number in hex
> from early uart
> 
> Hi Wei,
> 
> On 11/08/2021 11:23, Wei Chen wrote:
> > Current putn function that is using for early print
> > only can print low 32-bit of AArch64 register. This
> > will lose some important messages while debugging
> > with early console. For example:
> > (XEN) Bringing up CPU5
> > - CPU 0000000100000100 booting -
> > Will be truncated to
> > (XEN) Bringing up CPU5
> > - CPU 00000100 booting -
> >
> > In this patch, we increased the print loops and shift
> > bits to make putn print 64-bit number.
> >
> > Signed-off-by: Wei Chen <wei.chen@xxxxxxx>
> 
> Acked-by: Julien Grall <jgrall@xxxxxxxxxx>
> 
> > ---
> >   xen/arch/arm/arm64/head.S | 9 +++++----
> >   1 file changed, 5 insertions(+), 4 deletions(-)
> >
> > diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
> > index aa1f88c764..b32639d7d6 100644
> > --- a/xen/arch/arm/arm64/head.S
> > +++ b/xen/arch/arm/arm64/head.S
> > @@ -862,17 +862,18 @@ puts:
> >           ret
> >   ENDPROC(puts)
> >
> > -/* Print a 32-bit number in hex.  Specific to the PL011 UART.
> > +/* Print a 64-bit number in hex.  Specific to the PL011 UART.
> 
> As you modify the line, can you take the opportunity to write:
> 
> /*
>   * Print a 64-bit...
> 
> And also drop the second sentence as it the code has not been PL011
> specific for quite a while now.
> 

Ok, I will do it in next version

> >    * x0: Number to print.
> >    * x23: Early UART base address
> >    * Clobbers x0-x3 */
> > +#define PRINT_MASK 0xf000000000000000
> >   putn:
> >           adr   x1, hex
> > -        mov   x3, #8
> > +        mov   x3, #16
> >   1:
> >           early_uart_ready x23, 2
> > -        and   x2, x0, #0xf0000000    /* Mask off the top nybble */
> > -        lsr   x2, x2, #28
> > +        and   x2, x0, #PRINT_MASK    /* Mask off the top nybble */
> > +        lsr   x2, x2, #60
> >           ldrb  w2, [x1, x2]           /* Convert to a char */
> >           early_uart_transmit x23, w2
> >           lsl   x0, x0, #4             /* Roll it through one nybble at
> a time */
> >
> 
> Cheers,
> 
> --
> Julien Grall