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From: Ahmad Fatoum <a.fatoum@pengutronix.de>
To: Du Huanpeng <u74147@gmail.com>, barebox@lists.infradead.org
Subject: Re: [PATCH] MIPS: DEBUG_LL_UART_DIVISOR is 0, use a0 instead
Date: Fri, 11 Sep 2020 16:07:43 +0200	[thread overview]
Message-ID: <c56b316a-1fba-3e2e-530f-da5d9c810d1a@pengutronix.de> (raw)
In-Reply-To: <1599827638-15320-2-git-send-email-u74147@gmail.com>

On 9/11/20 2:33 PM, Du Huanpeng wrote:
> this make it possiable pass a0 as divisor to calculate uart baudrate
> in run time on boot.

This is not Ok. Your last commit has your board pass the divisor in a0 now, but other
boards, like the netgear-wg102, don't. Your change might break their UART because the
code there doesn't expect that a0 needs to have a valid value. If you want to do this,
you should migrate all users of this function all at once to supply a valid divisor
(probably `move a0, DEBUG_LL_UART_DIVISOR`).

It's same thing in C. You don't add a new parameter to a function without checking
that all callsites handle this correctly.

> 
> Signed-off-by: Du Huanpeng <u74147@gmail.com>
> ---
>  arch/mips/include/asm/debug_ll_ns16550.h | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/mips/include/asm/debug_ll_ns16550.h b/arch/mips/include/asm/debug_ll_ns16550.h
> index df58c4c..a33587a 100644
> --- a/arch/mips/include/asm/debug_ll_ns16550.h
> +++ b/arch/mips/include/asm/debug_ll_ns16550.h
> @@ -66,6 +66,9 @@ static inline void PUTC_LL(char ch)
>  	sb	t1, UART_LCR(t0)		/* Write it out */
>  
>  	li	t1, DEBUG_LL_UART_DIVISOR
> +#if DEBUG_LL_UART_DIVISOR == 0
> +	move	t1, a0
> +#endif
>  	sb	t1, UART_DLL(t0)		/* write low order byte */
>  	srl	t1, t1, 8
>  	sb	t1, UART_DLM(t0)		/* write high order byte */
> 

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  reply	other threads:[~2020-09-11 14:07 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-11 12:33 [PATCH] MIPS: loongson1: enable to run from spi flash Du Huanpeng
2020-09-11 12:33 ` [PATCH] MIPS: DEBUG_LL_UART_DIVISOR is 0, use a0 instead Du Huanpeng
2020-09-11 14:07   ` Ahmad Fatoum [this message]
2020-09-17 13:56     ` Du Huanpeng
2020-09-17 17:42       ` Ahmad Fatoum
2020-09-25 16:42         ` Du Huanpeng
2020-09-25 17:54           ` Ahmad Fatoum

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