linux-kernel - Re: [PATCH] atmel_serial: Split the interrupt handler

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Message-ID: <20071219141100.7384aff9@dhcp-252-066.norway.atmel.com>
Date:	Wed, 19 Dec 2007 14:11:00 +0100
From:	Haavard Skinnemoen <hskinnemoen@...el.com>
To:	"Remy Bohmer" <linux@...mer.net>
Cc:	"Andrew Victor" <linux@...im.org.za>,
	"ARM Linux Mailing List" <linux-arm-kernel@...ts.arm.linux.org.uk>,
	"Russell King - ARM Linux" <linux@....linux.org.uk>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] atmel_serial: Split the interrupt handler

On Wed, 19 Dec 2007 13:50:16 +0100
"Remy Bohmer" <linux@...mer.net> wrote:

> Hello Haavard,
> 
> > Hmm...perhaps we can eliminate the locking in the status handler
> > too...? Does anyone see a problem with this patch?  
> 
> I have not seen any problem so far, besides, I am very happy with a
> lockless interrupt handling, because this helps reducing latencies.
> 
> Tested it on top of the other 5 patches, and everything still works,
> also tested under stress conditions.
> 
> So:
> Acked-by: Remy Bohmer <linux@...mer.net>

Thanks. I think we can actually do it even simpler -- just check if any
of the relevant bits in pending are set, and schedule the tasklet if
they are.

Now, I suspect the locking is currently broken -- we need to guard
against updates to read_status_mask and ignore_status_mask, but I think
we can get away with only adding some locking to the tasklet, not the
interrupt handler.

Hrm. We probably need to lock while updating icount. That's a problem
since we do that from the tx interrupt handler...and I don't suppose we
want to move most of the atmel_tx_chars() code into the tasklet too...?

Haavard
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