Re: 2.4.21: Sharing interrupts with serial console

From: Chris Budd (budorola_at_gmail.com)
Date: 08/04/05

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    Date:	Thu, 4 Aug 2005 07:29:06 -0700
To: Chris Budd <budorola@gmail.com>, linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org

    On 8/4/05, Russell King <rmk+lkml@arm.linux.org.uk> wrote:
    > On Wed, Aug 03, 2005 at 06:36:51PM -0700, Chris Budd wrote:
    > > 1. The rs_init function in ./linux-2.4.21/drivers/char/serial.c
    > > explicitly states "The interrupt of the serial console port can't be
    > > shared." Does this include *ALL* interrupts? The code checks for
    > > sharing only with other serial devices, not *ALL* types of devices
    > > like I2C, RTC, etc.
    <snip>
    > > 2. While the presence of the comment about not sharing was nice, it
    > > does not explain "why?"
    >
    > Connecting a level-active interrupt output to an edge-triggered
    > interrupt controller input is Bad News(tm) for missing interrupts.
    >

    Of course. I thought it was something more serious in the bowels of
    the kernel. All the comment needed was just that one adjective "The
    *edge-triggered* interrupt of the serial console port can't be
    shared." I know many programmers do not like to write comments, but
    good comments make the code more robust and stable: the code clearly
    shows *what* you did, but comments are necessary to indicate *why*.

    <snip>
    > If your Intel hardware doesn't have level triggered input capabilities,
    > please apply customer pressure to Intel to ensure that they consider it
    > for their future ARM-based designs.

    You will be happy to know that the Intel IOP80321 has level-sensitive
    interrupts.

    Thank you for the detailed explanation.
    Chris.
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