Hello, On 9/17/20 3:56 PM, Du Huanpeng wrote: > Hi, this patch should not intoduce any regression to existing boards, > because: > > 1. pass divisor by DEBUG_LL_UART_DIVISOR > > #define DEBUG_LL_UART_DIVISOR NUMBER > > which the ``NUMBER'' is not ``0'' (zero). In this case, this patch > has no effect and this line of code will be removed by preprocessor, > before compile :) > move t1, a0 > > 2. Pass divisor by a0 > > #define DEBUG_LL_UART_DIVISOR 0 > > recalculate the divisor is needed when the pll/div setting is changed > outside of barebox. e.g. ejtag. and load barebox and run in ram. > > Because 0 maybe an invalid value for a divisor, so I take this value for > a hint to pass a0 as divisor. this will not conflict with other boards > which pass divisor by defining DEBUG_LL_UART_DIVISOR with a valied value. I guess we can agree that debug_ll_ns16550_init( #if DEBUG_LL_UART_DIVISOR int a0 #endif ); is not the best way to go about it, so why do its equivalent in assembly? >> you should migrate all users of this function all at once to supply a valid divisor >> (probably `move a0, DEBUG_LL_UART_DIVISOR`). > > MIPS use ``li'' load immediate, and move to copy inter registers. > so, maybe change my patch to: > > #if DEBUG_LL_UART_DIVISOR > li t1, DEBUG_LL_UART_DIVISOR > #else > move t1, a0 > #endif I'd prefer you keep it as move t1, a0 without an ifdef and move the argument passing out of debug_ll_ns16550_init. Cheers Ahmad > > - - - > or even do a bit tricky: > > --- a/arch/mips/include/asm/debug_ll_ns16550.h > +++ b/arch/mips/include/asm/debug_ll_ns16550.h > @@ -65,7 +65,7 @@ static inline void PUTC_LL(char ch) > li t1, UART_LCR_DLAB /* DLAB on */ > sb t1, UART_LCR(t0) /* Write it out */ > > - li t1, DEBUG_LL_UART_DIVISOR > + add t1, zero, DEBUG_LL_UART_DIVISOR > sb t1, UART_DLL(t0) /* write low order byte */ > srl t1, t1, 8 > sb t1, UART_DLM(t0) /* write high order byte */ > -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | _______________________________________________ barebox mailing list barebox@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/barebox
