linux-kernel - Re: [PATCH] serial: 8250 check iir rdi in interrupt

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Message-ID: <CAJ0e-Fqzq6s6H=9CMpqJKug2=oR89_qw_52Yz-ihJd-8Bc-_+Q@mail.gmail.com>
Date:	Fri, 26 Oct 2012 14:57:31 -0700
From:	Min Zhang <mzhang@...sta.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	gregkh@...uxfoundation.org, linux-serial@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] serial: 8250 check iir rdi in interrupt

On Fri, Oct 26, 2012 at 7:19 AM, Alan Cox <alan@...rguk.ukuu.org.uk> wrote:

> So we only need to check this in serial8250_handle_irq when IIR indicates
> a data timeout interrupt ?
>
> Can we do
>
>         if ((iir & 0x0F) == 0x0C) {
>                 /* Expensive RDI check */
>         }
>
>
>
> Alan

Checking data timeout interrupt is only for "too much work for irq"
problem. There is another console freeze problem which is caused by
reading receive FIFO when there is no RDI interrupt, such as during
THRI transmit interrupt, so no timeout interrupt. This time one has to
check two both IIR and LSR. After all these checking, it becomes the
original patch anyway.

I am posting another simpler revision to exclude timer handler from
this workaround, and make this workaround default off and inline.
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