Messages in this thread | | | Date | Fri, 13 May 2005 20:37:35 +0100 | From | Russell King <> | Subject | Re: tickle nmi watchdog whilst doing serial writes. |
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On Fri, May 13, 2005 at 09:14:52PM +0200, Arjan van de Ven wrote: > On Fri, 2005-05-13 at 14:48 -0400, Dave Jones wrote: > > if (up->port.flags & UPF_CONS_FLOW) { > > tmout = 1000000; > > while (--tmout && > > - ((serial_in(up, UART_MSR) & UART_MSR_CTS) == 0)) > > + ((serial_in(up, UART_MSR) & UART_MSR_CTS) == 0)) { > > udelay(1); > > + touch_nmi_watchdog(); > > + } > > } > > } > > > > > > We *could* tickle it less often, but given we're busy waiting anyway > > it probably doesnt make sense to not favour the more simple approach. > > Hmm, maybe we want a cpu_relax() in there too. opinions? > > udelay() includes cpu_relax() already so that is futile. > > However.. this is a hack. Do we really need to do busy waiting here for > this long??
Of course you do. Think about CTS flow control where the other end is also busy and has to drain its tty buffers before it can allow the remote end to proceed. (And who says its another Linux box anyway?)
However, if people are using CTS flow control, they want reliable logging. Therefore, it's even questionable whether we should even time out (but we do to keep the system "running".)
-- 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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