From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D49DCD1036C for ; Tue, 25 Nov 2025 23:46:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=FesFCToQspFq4tboaTqpc09nhNIi95vNt6BcM6NYbRs=; b=l/BX4l+RJCgVO9Ilcp41BYvSil Ysof6tZGTUSdcvLqTgYXoR/y6s1/Aw5tAIxTDGvRMP/O1T3w7d/092Xktx/PahYaz4pFAr1ig2HIw 7X6W2IocpO5sQaP81wsRDAUDEjkIZnGTG3NtVcKnG5Yt8VGvGTMym+2h7900JWhqSxu8uU7qtG4bz 0Ww06LZECzQBbhWxqLKgqoznxbVFHZBW4l0DG1F+uPMY5GmqkaurO5oCJoN+RKY0+NS0oA9ZxY1Xh tz3abSCfUuPlVkecBwdZW+cxKlDMMeslqvVMysJnkn8F6hT4tTZVgF7MOhCKt0YRJpWEZPrScVTGa hd77C55g==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vO2jt-0000000E5Nz-2kKI; Tue, 25 Nov 2025 23:46:29 +0000 Received: from pandora.armlinux.org.uk ([2001:4d48:ad52:32c8:5054:ff:fe00:142]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1vO2jp-0000000E5NW-2nyy for linux-arm-kernel@lists.infradead.org; Tue, 25 Nov 2025 23:46:26 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=armlinux.org.uk; s=pandora-2019; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=FesFCToQspFq4tboaTqpc09nhNIi95vNt6BcM6NYbRs=; b=JM4HoprP8viQFMd9g0NmwQ7Z+m P6KgwuM1w2Xv6t0AvfTeIFpxQTgS0JCfDlUY/iEDwfBs47gjc4nIgo7+Z5C8OVZOniW9X6uf9vi+O Plb3ePl2i25w9iKdUkQD1ts9YtaCNRW+I+Lc3mqvvWXY4zeU3Z8Y8KkhZq/8OVgtDGF54X1Su2Z8P 3pnWpArvQR0FsAaz6y5ib5oCd1m6DZlSBiz7TDUSo/oY3o9CCvCtk5JGuorLvkF3CsQuE57TM86Zr gdMe5sHAGAbp8ittT6Ba+z1ZPE3P0W8lMMIcM4DoILl7fBrgVMAIno3unY3eTN9bt/TEEOAumgnw4 1wrLg4hg==; Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:40256) by pandora.armlinux.org.uk with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.98.2) (envelope-from ) id 1vO2jf-000000003Ju-1d1K; Tue, 25 Nov 2025 23:46:15 +0000 Received: from linux by shell.armlinux.org.uk with local (Exim 4.98.2) (envelope-from ) id 1vO2jc-000000001BP-2gpy; Tue, 25 Nov 2025 23:46:12 +0000 Date: Tue, 25 Nov 2025 23:46:12 +0000 From: "Russell King (Oracle)" To: rohan.g.thomas@altera.com Cc: Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Maxime Coquelin , Alexandre Torgue , Maxime Chevallier , netdev@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Matthew Gerlach Subject: Re: [PATCH net-next] net: stmmac: dwmac: Disable flushing frames on Rx Buffer Unavailable Message-ID: References: <20251126-a10_ext_fix-v1-1-d163507f646f@altera.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251126-a10_ext_fix-v1-1-d163507f646f@altera.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251125_154625_727570_76590901 X-CRM114-Status: GOOD ( 16.63 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Nov 26, 2025 at 12:37:12AM +0800, Rohan G Thomas via B4 Relay wrote: > From: Rohan G Thomas > > In Store and Forward mode, flushing frames when the receive buffer is > unavailable, can cause the MTL Rx FIFO to go out of sync. This results > in buffering of a few frames in the FIFO without triggering Rx DMA > from transferring the data to the system memory until another packet > is received. Once the issue happens, for a ping request, the packet is > forwarded to the system memory only after we receive another packet > and hece we observe a latency equivalent to the ping interval. > > 64 bytes from 192.168.2.100: seq=1 ttl=64 time=1000.344 ms > > Also, we can observe constant gmacgrp_debug register value of > 0x00000120, which indicates "Reading frame data". > > The issue is not reproducible after disabling frame flushing when Rx > buffer is unavailable. But in that case, the Rx DMA enters a suspend > state due to buffer unavailability. To resume operation, software > must write to the receive_poll_demand register after adding new > descriptors, which reactivates the Rx DMA. This seems like a sensible writeup, which all seems to make sense, even though the databook I have seems vague on the effect of the DFF bit. > This issue is observed in the socfpga platforms which has dwmac1000 IP > like Arria 10, Cyclone V and Agilex 7. Issue is reproducible after > running iperf3 server at the DUT for UDP lower packet sizes. > > Signed-off-by: Rohan G Thomas > Reviewed-by: Matthew Gerlach Given the above, that Maxime has also tested it which shows a net benefit, and I've looked through this, even though I can't positively say it's correct due to the databook vagueness: Reviewed-by: Russell King (Oracle) Thanks! -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!