Subject: Re: [PATCH] ppc32: fix cpm_uart_int() missing interrupts

From: Guillaume Autran <[email-masked]>
Date: Thu, 19 May 2005 16:36:35 -0400

One thought though, if the event register is cleared _before_  the event 
is processed (clearing the cause), will the cpm set the bit again 
(before we have time to clear the cause) ? That would generate 2 
interrupts for the same event ? Am I right ?

Guillaume Autran wrote:

> You are right, moving the event clearing statement is much easier and 
> cleaner. Let the interrupt be the loop.
> Thanks Dan !
>
>
> Dan Malek wrote:
>
>>
>> On May 19, 2005, at 3:34 PM, Guillaume Autran wrote:
>>
>>> Is it better like this ?
>>
>>
>>
>> Yes, but now I see one problem with it.  :-)
>>
>> We have to clear all events even though we may not
>> handle all of them.  Your while loop filters only the events
>> we process, but there could be others causing the interrupt
>> which will never get cleared.  In this case we end up with
>> an infinite interrupt loop where we don't process anything,
>> but we don't make the interrupt go away, either.   It may be
>> easier to forget the loop, just read/clear the event register
>> up front, then process based on the events based upon
>> what we found. It's what we tend to do in the other drivers.
>>
>> The functions called to do the rx/tx processing have loops
>> in them to process all of the data they find, so it isn't likely
>> you have left anything behind.  If you want to try to save
>> the interrupt overhead, change it to do/while, check again
>> at the end before the exit.
>>
>> Thanks.
>>
>>
>>     -- Dan
>>
>
>------------------------------------------------------------------------
>
>diff -Nru linux-2.6.12-rc4.org/drivers/serial/cpm_uart/cpm_uart_core.c linux-2.6.12-rc4.new/drivers/serial/cpm_uart/cpm_uart_core.c
>--- linux-2.6.12-rc4.org/drivers/serial/cpm_uart/cpm_uart_core.c	2005-05-07 01:20:31.000000000 -0400
>+++ linux-2.6.12-rc4.new/drivers/serial/cpm_uart/cpm_uart_core.c	2005-05-19 16:23:13.000000000 -0400
>@@ -336,22 +336,22 @@
> 
> 	if (IS_SMC(pinfo)) {
> 		events = smcp->smc_smce;
>+		smcp->smc_smce = events;
> 		if (events & SMCM_BRKE)
> 			uart_handle_break(port);
> 		if (events & SMCM_RX)
> 			cpm_uart_int_rx(port, regs);
> 		if (events & SMCM_TX)
> 			cpm_uart_int_tx(port, regs);
>-		smcp->smc_smce = events;
> 	} else {
> 		events = sccp->scc_scce;
>+		sccp->scc_scce = events;
> 		if (events & UART_SCCM_BRKE)
> 			uart_handle_break(port);
> 		if (events & UART_SCCM_RX)
> 			cpm_uart_int_rx(port, regs);
> 		if (events & UART_SCCM_TX)
> 			cpm_uart_int_tx(port, regs);
>-		sccp->scc_scce = events;
> 	}
> 	return (events) ? IRQ_HANDLED : IRQ_NONE;
> }
>  
>
>------------------------------------------------------------------------
>
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-- 
=======================================
Guillaume Autran
Senior Software Engineer
MRV Communications, Inc.
Tel: (978) 952-4932 office
E-mail: [email-masked]
=======================================