From: Russell King <rmk+lkml@arm.linux.org.uk>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Serial: bug in 8250.c when handling PCI or other level triggers
Date: Wed, 14 Dec 2005 19:55:00 +0000 [thread overview]
Message-ID: <20051214195459.GG7124@flint.arm.linux.org.uk> (raw)
In-Reply-To: <1134587288.25663.61.camel@localhost.localdomain>
On Wed, Dec 14, 2005 at 07:08:08PM +0000, Alan Cox wrote:
> On Mer, 2005-12-14 at 16:55 +0000, Russell King wrote:
> > If we trigger this, we can assume that the port is dead anyway, or
> > we're in a situation where the host CPU can not keep up with the
> > data stream.
>
> Not actually true in some cases.
>
> - When your UART has a large FIFO and pretends to be an 8250 you can get
> a 256 byte burst triggered by the box sleeping for a moment or the BIOS
> SMI crap going to chat to the battery
In which case the receive_chars() function gobbles up to 255 characters
from the device before relinquishing to the main interrupt loop. The
main interrupt loop has two exit conditions - no further interrupts
are pending from any device, or we run this loop 256 times.
In the case where further characters are waiting, we will re-run the
receive_chars() function.
Hence, we will check the device up to 256 times and each will potentially
receive 255 characters, which gives about 64K of character reception
before the warning triggers.
Therefore, this scenario is _very_ _very_ unlikely.
> - On a virtualised system this trap can trigger because the emulations
> don't emulate the bit arrival and baud rate.
Again, only if there's more than about 64K of data waiting.
--
Russell King
Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/
maintainer of: 2.6 Serial core
prev parent reply other threads:[~2005-12-14 19:55 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-12-14 15:23 Serial: bug in 8250.c when handling PCI or other level triggers Alan Cox
2005-12-14 16:07 ` Meelis Roos
2005-12-14 17:24 ` Russell King
2005-12-14 18:43 ` Meelis Roos
2005-12-21 15:24 ` Russell King
2005-12-21 20:33 ` Meelis Roos
2005-12-21 22:15 ` Russell King
2005-12-22 10:35 ` Meelis Roos
2005-12-22 13:07 ` Russell King
2005-12-22 13:19 ` Meelis Roos
2005-12-23 9:20 ` Meelis Roos
2005-12-23 9:33 ` Russell King
2005-12-23 10:05 ` Meelis Roos
2005-12-23 10:41 ` Russell King
2005-12-27 13:54 ` Meelis Roos
2005-12-28 19:55 ` Russell King
2005-12-29 8:11 ` Meelis Roos
2006-01-08 23:24 ` Antonio Vargas
2006-01-09 8:54 ` Russell King
2005-12-14 22:29 ` Alan Cox
2005-12-15 19:00 ` Stuart MacDonald
2005-12-14 16:55 ` Russell King
2005-12-14 19:08 ` Alan Cox
2005-12-14 19:55 ` Russell King [this message]
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