linux-kernel - Re: [PATCH v2 1/5] ethernet: add sun8i-emac driver

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Date:	Fri, 29 Jul 2016 11:26:57 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	LABBE Corentin <clabbe.montjoie@...il.com>
Cc:	linux-arm-kernel@...ts.infradead.org, robh+dt@...nel.org,
	mark.rutland@....com, maxime.ripard@...e-electrons.com,
	wens@...e.org, linux@...linux.org.uk, davem@...emloft.net,
	devicetree@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-sunxi@...glegroups.com
Subject: Re: [PATCH v2 1/5] ethernet: add sun8i-emac driver

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