linux-kernel - Re: [PATCH] net/cadence/macb: clear interrupts simply and correctly

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Date:	Mon, 16 Jun 2014 20:50:17 -0700
From:	Sören Brinkmann <soren.brinkmann@...inx.com>
To:	Jongsung Kim <neidhard.kim@....com>
CC:	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	"David S. Miller" <davem@...emloft.net>,
	Hayun Hwang <hwang.hayun@....com>,
	Youngkyu Choi <youngkyu7.choi@....com>
Subject: Re: [PATCH] net/cadence/macb: clear interrupts simply and correctly

On Tue, 2014-06-17 at 11:38AM +0900, Jongsung Kim wrote:
> On 06/16/2014 11:56 PM, Sören Brinkmann wrote:
> > On Mon, 2014-06-16 at 02:00PM +0900, Jongsung Kim wrote:
> >> On 06/13/2014 12:44 AM, Sören Brinkmann wrote:
> >>> This is now clearing all IRQ flags which is probably not what we want
> >>> here. This is handling RX only. We still want the non-RX interrupts to go to
> >>> the actual interrupt service routing.
> >>
> >> The ISR(Interrupt Status Register) is read only in the interrupt service
> >> routine, macb_interrupt. But is partially cleared here and there. Further
> >> handler-functions decide jobs to be done by reading/checking other status
> >> registers. (e.g., TSR, RSR) So, clearing the ISR after reading looks not
> >> a bad idea.
> >
> > But you are clearing _all_ interrupt flags in the RX NAPI handler.
> > Doesn't that mean we might miss certain events?
> 
> Please inspect my patch again. What I did in the macb_poll is removing
> statements clearing the Rx-complete interrupt, not clearing all the
> interrupts.

Oh, you're right. I misread the patch, sorry. The call to macb_read_isr was
already a different hunk.
Why is clearing those bits removed? It's probably not a big hit, but it might
result in a pointless interrupt which could be avoided. But it should
probably clear all RX interrupts - MACB_RX_INT_FLAGS - instead of just RCOMP.
For clear-on-read implementations it shouldn't make a difference.

And in the if-condition in that new helper, I'd add '&& status' to
avoid writing back zeros.

	Thanks,
	Sören
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