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[82.37.195.13]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-493e0078d49sm47904175e9.0.2026.07.07.02.48.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 07 Jul 2026 02:48:52 -0700 (PDT) Date: Tue, 7 Jul 2026 10:48:50 +0100 From: Daniel Thompson To: Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Maxime Coquelin , Alexandre Torgue , Alexei Starovoitov , Daniel Borkmann , Jesper Dangaard Brouer , John Fastabend , Stanislav Fomichev Cc: Alex Elder , netdev@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org Subject: Re: [PATCH] net: stmmac: Avoid freeing and re-requesting IRQ during XDP set prog Message-ID: References: <20260706-tc956x-stmmac-no_irq_teardown-v1-1-df009d0272bf@riscstar.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260706-tc956x-stmmac-no_irq_teardown-v1-1-df009d0272bf@riscstar.com> On Mon, Jul 06, 2026 at 05:17:58PM +0100, Daniel Thompson wrote: > Currently stmmac will run a full cycle of IRQ tear down and setup when > setting up a new XDP program. This makes tuning TSN systems difficult > because whenever a new XDP program is installed then the irq threads will > be stopped and restarted which will undo any thread tuning. > > The problem is avoided by removing stmmac_free_irq()/stmmac_request_irq() > from stmmac_xdp_release()/stmmac_xdp_open(). > > stmmac_free_irq() implicitly synchronizes interrupts and, with that > removed, I was unable to prove that later actions in > stmmac_xdp_release() are safe when there are concurrent interrupts. To > avoid problems let's also move the code to disable DMA interrupts earlier > in the sequence and explicitly sync the interrupts handler(s). > > Signed-off-by: Daniel Thompson > > @@ -7156,10 +7201,8 @@ int stmmac_xdp_open(struct net_device *dev) > stmmac_reset_queues_param(priv); > > /* DMA CSR Channel configuration */ > - for (chan = 0; chan < dma_csr_ch; chan++) { > + for (chan = 0; chan < dma_csr_ch; chan++) > stmmac_init_chan(priv, priv->ioaddr, priv->plat->dma_cfg, chan); > - stmmac_disable_dma_irq(priv, priv->ioaddr, chan, 1, 1); > - } Sashiko picked up that stmmac_init_chan() has the effect of enabling DMA irqs, making this code unsafe. Given stmmac_xdp_open() can only be called on a running interface (and that stmmac_xdp_open() explicitly sets sph) then re-initializing with stmmac_init_chan() should have no effect and we can drop that as well. I'll double check with a code review across all the dwmac versions before pushing out a v2! Daniel.