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Date: Fri, 18 Sep 2026 22:31:01 +0200
From: Nicolai Buchwitz <nb@tipi-net.de>
To: =?UTF-8?Q?Th=C3=A9o_Lebrun?= <theo.lebrun@bootlin.com>
Cc: Conor Dooley <conor.dooley@microchip.com>, Andrew Lunn
 <andrew+netdev@lunn.ch>, "David S. Miller" <davem@davemloft.net>, Eric
 Dumazet <edumazet@google.com>, Jakub Kicinski <kuba@kernel.org>, Paolo Abeni
 <pabeni@redhat.com>, Simon Horman <horms@kernel.org>, Nicolas Ferre
 <nicolas.ferre@microchip.com>, Sean Anderson <sean.anderson@linux.dev>,
 Antoine Tenart <atenart@kernel.org>, netdev@vger.kernel.org,
 linux-kernel@vger.kernel.org, Vladimir Kondratiev
 <vladimir.kondratiev@mobileye.com>, Gregory CLEMENT
 <gregory.clement@bootlin.com>, Tawfik Bayouk <tawfik.bayouk@mobileye.com>,
 Thomas Petazzoni <thomas.petazzoni@bootlin.com>, stable@vger.kernel.org
Subject: Re: [PATCH net] net: macb: take bp->lock around NCR
 read-modify-writes
In-Reply-To: <20260918-macb-ncr-rmw-v1-1-30c3494f93cd@bootlin.com>
References: <20260918-macb-ncr-rmw-v1-1-30c3494f93cd@bootlin.com>
Message-ID: <f695ad9aa88acb08727f442307dafe9c@tipi-net.de>
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Hi Théo

On 18.9.2026 21:59, Théo Lebrun wrote:
> NCR is read-modify-written from many contexts:
> 
>  - macb_mac_link_down() clears RE|TE,
>  - macb_mac_link_up() sets RE|TE|PTPUNI,
>  - macb_hresp_error_task() clears then re-sets RE|TE,
>  - macb_start_xmit() / macb_tx_restart() / macb_tx_error_task() set
>    TSTART (already under bp->lock),
>  - macb_interrupt() might toggle RE (also under bp->lock).
> 
> The first three risk concurrent RMW with anyone from the list as they
> don't grab bp->lock.

There is a fourth, in at91ether_interrupt():

      if (intstatus & MACB_BIT(RXUBR)) {
              ctl = macb_readl(bp, NCR);
              macb_writel(bp, NCR, ctl & ~MACB_BIT(RE));
              wmb();
              macb_writel(bp, NCR, ctl | MACB_BIT(RE));
      }

I guess you have skipped this as the emac variants using this are not 
SMP?

> [...]

Reviewed-by: Nicolai Buchwitz <nb@tipi-net.de>

Regards
Nicolai