linux-kernel - Re: [PATCH 06/18] Blackfin Serial Driver: explain why we cannot cpu

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Message-Id: <20090306143816.ed70f0e1.akpm@linux-foundation.org>
Date:	Fri, 6 Mar 2009 14:38:16 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Bryan Wu <cooloney@...nel.org>
Cc:	alan@...rguk.ukuu.org.uk, linux-kernel@...r.kernel.org,
	vapier.adi@...il.com, cooloney@...nel.org
Subject: Re: [PATCH 06/18] Blackfin Serial Driver: explain why we cannot
 cpu_relax() in early serial code

On Fri,  6 Mar 2009 14:42:48 +0800
Bryan Wu <cooloney@...nel.org> wrote:

> From: Mike Frysinger <vapier.adi@...il.com>
> 
> Signed-off-by: Mike Frysinger <vapier.adi@...il.com>
> Signed-off-by: Bryan Wu <cooloney@...nel.org>
> ---
>  drivers/serial/bfin_5xx.c |    4 ++++
>  1 files changed, 4 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/serial/bfin_5xx.c b/drivers/serial/bfin_5xx.c
> index 5a163f6..de8709d 100644
> --- a/drivers/serial/bfin_5xx.c
> +++ b/drivers/serial/bfin_5xx.c
> @@ -1190,6 +1190,10 @@ static __init void early_serial_putc(struct uart_port *port, int ch)
>  	unsigned timeout = 0xffff;
>  	struct bfin_serial_port *uart = (struct bfin_serial_port *)port;
>  
> +	/* We cannot cpu_relax() here as doing so on the BF561 relies
> +	 * on the per-cpu region being setup, and since this is early
> +	 * serial code, it may not yet be usable ...
> +	 */
>  	while ((!(UART_GET_LSR(uart) & THRE)) && --timeout)
>  		barrier();

Again: this is blackfin core breakage.
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