Messages in this thread | | | Date | Wed, 14 Dec 2005 19:55:00 +0000 | From | Russell King <> | Subject | Re: Serial: bug in 8250.c when handling PCI or other level triggers |
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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 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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