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

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Date:	Tue, 17 Jun 2014 13:42:47 +0900
From:	Jongsung Kim <neidhard.kim@....com>
To:	Sören Brinkmann <soren.brinkmann@...inx.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 06/17/2014 12:50 PM, Sören Brinkmann wrote:
> 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.
> 
> 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.

I agree. But I removed it because I think stepping the same procedure
regardless of the "gem_irq_clear_read" implementation is better than
implementation-specific optimization.

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

Good point. I'll add it when I resend v2.

Jongsung
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