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([39.170.101.209]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-84e5341e69esm3740869b3a.43.2026.07.27.20.44.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 27 Jul 2026 20:44:17 -0700 (PDT) From: Zxyan Zhu To: Jakub Kicinski Cc: Maxime Chevallier , Andrew Lunn , "David S . Miller" , Eric Dumazet , Paolo Abeni , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Zxyan Zhu Subject: Re: [PATCH net-next] net: stmmac: dwxgmac2: configure INTM for per-channel interrupt routing Date: Tue, 28 Jul 2026 11:43:03 +0800 Message-Id: <20260728034303.1432292-1-zxyan0222@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260727181617.19604f9c@kernel.org> References: <20260727181617.19604f9c@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit On Mon, 27 Jul 2026 18:16:17 -0700 Jakub Kicinski wrote: > On Thu, 23 Jul 2026 15:50:50 +0200 Maxime Chevallier wrote: > > Same logic as in dwmac4, this looks good to me, > > Is this a fix tho? The commit message reads like DMA irqs are > completely ignored. But neither this commit nor 6ccf12ae111e > really explain much to an outsider.. Thanks for the review. The commit message does a poor job of explaining the actual impact, so let me clarify. I've verified on hardware with XGMAC and multi-MSI enabled. The results are definitive: INTM=00 (default): - 5.4 million interrupts on the common IRQ line in 3 seconds - ~1.8 million IRQ_NONE returns per second INTM=01: - 0 interrupts on the common IRQ line - Per-channel IRQs work normally - 10G line rate works correctly The behavior is that with INTM=00, sbd_intr_o is also asserted for each DMA completion event. The common IRQ handler stmmac_mac_interrupt() only processes MAC-layer events (LPI, PMT, timestamps) and returns IRQ_NONE for DMA completion events, causing the interrupt storm. With INTM=01, sbd_intr_o is not asserted for DMA transfer completion events, which is the correct mode for per-channel interrupt routing. Regarding net vs net-next: XGMAC multi-MSI has never worked correctly since it was introduced, so this is not a regression. The same INTM=1 configuration for GMAC4 was merged via net-next (6ccf12ae111e "net: stmmac: use interrupt mode INTM=1 for multi-MSI"). I'm leaning toward net-next for consistency, but since this makes multi-MSI completely non-functional without it, I'd appreciate your opinion on whether net is more appropriate.