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Re: [Xen-devel] [PATCH] xen: more robust serial port driver

To: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-devel] [PATCH] xen: more robust serial port driver
From: Christoph Egger <Christoph.Egger@xxxxxxx>
Date: Tue, 28 Jul 2009 16:47:36 +0200
Cc: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
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On Tuesday 28 July 2009 16:15:42 Keir Fraser wrote:
> On 28/07/2009 15:07, "Christoph Egger" <Christoph.Egger@xxxxxxx> wrote:
> > Attached patch adds a check if the fifo is usable before we
> > actually use it.
> I count that at least the first two chunks and the initialisation of
> tx_fifo_size are unnecessary.

First hunk:

    It looks suspicious returning a value of type void.

Second hunk and initialization of tx_fifo_size:

    If you are sure these initializations are duplicates, then they are

> Might this be the case for the udelay(100) as 
> well?

No. This ensures, that the write takes effect before the read happens.

> And what kinds of systems have these broken UARTs that half-advertise 
> a broken/non-existent FIFO?

The original ns16550 has a broken FIFO. The ns16450 has no FIFO.
There are simulators which simulate those old things instead of a ns16550a.


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