From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [PATCH v2 1/5] ethernet: add sun8i-emac driver Date: Fri, 29 Jul 2016 11:26:57 +0200 Message-ID: <4552489.XcKoxjnXeP@wuerfel> References: <1469001800-11615-1-git-send-email-clabbe.montjoie@gmail.com> <4697175.RMdFEWr9V5@wuerfel> <20160728131826.GA7582@Red> Reply-To: arnd-r2nGTMty4D4@public.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Return-path: Sender: linux-sunxi-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org In-Reply-To: <20160728131826.GA7582@Red> List-Post: , List-Help: , List-Archive: , List-Unsubscribe: , To: LABBE Corentin Cc: linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, mark.rutland-5wv7dgnIgG8@public.gmane.org, maxime.ripard-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org, wens-jdAy2FN1RRM@public.gmane.org, linux-I+IVW8TIWO2tmTQ+vhA3Yw@public.gmane.org, davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-sunxi-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org List-Id: devicetree@vger.kernel.org On Thursday, July 28, 2016 3:18:26 PM CEST LABBE Corentin wrote: > > I will reworked locking and it seems that no locking is necessary. > I have added the following comment about the locking strategy: > > /* Locking strategy: > * RX queue does not need any lock since only sun8i_emac_poll() access it. > * (All other RX modifiers (ringparam/ndo_stop) disable NAPI and so sun8i_emac_poll()) > * TX queue is handled by sun8i_emac_xmit(), sun8i_emac_complete_xmit() and sun8i_emac_tx_timeout() > * (All other RX modifiers (ringparam/ndo_stop) disable NAPI and stop queue) > * > * sun8i_emac_xmit() could fire only once (netif_tx_lock) > * sun8i_emac_complete_xmit() could fire only once (called from NAPI) > * sun8i_emac_tx_timeout() could fire only once (netif_tx_lock) and couldnt > * race with sun8i_emac_xmit (due to netif_tx_lock) and with sun8i_emac_complete_xmit which disable NAPI. > * > * So only sun8i_emac_xmit and sun8i_emac_complete_xmit could fire at the same time. > * But they never could modify the same descriptors: > * - sun8i_emac_complete_xmit() will modify only descriptors with empty status > * - sun8i_emac_xmit() will modify only descriptors set to DCLEAN > * Proper memory barriers ensure that descriptor set to DCLEAN could not be > * modified latter by sun8i_emac_complete_xmit(). > * */ Sounds good, the comment is certainly very helpful here. Arnd