From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH 1/2] net: fec: don't ack masked interrupt events Date: Wed, 06 Dec 2017 15:47:37 -0500 (EST) Message-ID: <20171206.154737.1480687559470751883.davem@davemloft.net> References: <20171206172459.14059-1-l.stach@pengutronix.de> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: fugang.duan@nxp.com, netdev@vger.kernel.org, patchwork-lst@pengutronix.de, kernel@pengutronix.de To: l.stach@pengutronix.de Return-path: Received: from shards.monkeyblade.net ([184.105.139.130]:55100 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751711AbdLFUri (ORCPT ); Wed, 6 Dec 2017 15:47:38 -0500 In-Reply-To: <20171206172459.14059-1-l.stach@pengutronix.de> Sender: netdev-owner@vger.kernel.org List-ID: From: Lucas Stach Date: Wed, 6 Dec 2017 18:24:58 +0100 > The FEC doesn't have a real interrupt status register, that takes > into account the mask status of the IRQ. The driver reads the raw > interrupt event register, which also reports events for masked > IRQs. > > The driver needs to apply the current mask itself, to avoid acking > IRQs that are currently masked, as NAPI relies on the masking to > hide the IRQs. The current behavior of just acking all interrupts > regardless of their mask status opens the driver up the "rotting > packet" race-window, as described in the original NAPI-HOWTO, which > has been observed in the wild. > > Signed-off-by: Lucas Stach > --- > drivers/net/ethernet/freescale/fec_main.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c > index 610573855213..0b70c07eb703 100644 > --- a/drivers/net/ethernet/freescale/fec_main.c > +++ b/drivers/net/ethernet/freescale/fec_main.c > @@ -1584,7 +1584,8 @@ fec_enet_interrupt(int irq, void *dev_id) > uint int_events; > irqreturn_t ret = IRQ_NONE; > > - int_events = readl(fep->hwp + FEC_IEVENT); > + int_events = readl_relaxed(fep->hwp + FEC_IEVENT) & > + readl_relaxed(fep->hwp + FEC_IMASK); Adding a full new MMIO register read to every interrupt is going to make interrupts significantly more expensive. You should cache this mask in software in order to avoid the expensive MMIO read. Thanks.