linux-kernel - Re: [PATCH] Linux always started with 9600 8N1

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Message-Id: <20070527.141622.30184020.davem@davemloft.net>
Date:	Sun, 27 May 2007 14:16:22 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	jengelh@...ux01.gwdg.de
Cc:	sparclinux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Linux always started with 9600 8N1

From: Jan Engelhardt <jengelh@...ux01.gwdg.de>
Date: Sun, 27 May 2007 18:44:18 +0200 (MEST)

> 
> On May 26 2007 15:47, David Miller wrote:
> >> I have set the OBP to run at 115200, also set agetty on ttyS0 to do the 
> >> same, and also added console=ttyS0,115200 to silo.conf (and also tried 
> >> console=ttyS0,115200n8). But! Linux still gives me 9600 8N1. The ominous 
> >> double screen blanking (why is that done anyway?) already takes place 
> >> with 9600. I smell a bug. What do you think?
> >
> >The code in drivers/serial/suncore.c:sunserial_console_termios()
> >should be parsing your OBP settings, add some tracing and see why it
> >isn't working.
> >
> >Please track the bug down for us, thanks :-)
> 
> Just why did no one get a kernel oops? After all, the code tried to
> write to constant memory.
> 
> This is the first patch of two. There is yet another section of Linux 
> code that runs in 9600-only, and I need to figure out which.

There should not be an OOPS, we don't map any section of the
kernel as read-only or execute-only or anything like that.

The kernel image is mapped with full read/write/execute permission.

So even writes to so-called 'read-only' sections of the kernel image
will work and therefore I don't understand what the bug could be other
than the compiler "optimizing" away the write to the constant string
in which case the compiler should have warned about it.
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