From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from pandora.armlinux.org.uk (pandora.armlinux.org.uk [78.32.30.218]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7789A25CC63; Tue, 25 Nov 2025 23:46:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=78.32.30.218 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764114386; cv=none; b=TGTaCGVcRCarnk/0Zzo1Jc8+ild7JVmnQfmd0XV8/pB4miATrfgYAupguyUHWdImwDOvgIRQ4bS1ZxvBWCFLcIz89/72dLuITR8waDiHNOb7jjVj5hmhNqUG4/nQdrXd6ZCLsdsxZcAiZ1ZHuHI7MNy4azg4llRsuFKbaAvtUMU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764114386; c=relaxed/simple; bh=tDHiPPgQDE5xWH9oEyQV1NNg+Ujnwp+DjuvV0gjTwFo=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=eUd2r6loPPGCctjgsLM21PKlGAmIq50r2vi18AtKJp1rWFJjjZcIeUdWOT0kSzONIqhlV/WUn3s8W9PFbQtdQH8RJVGJp/vmWD38BMyU0BtVFhrtLWv0PtH6eVMLhdGu7j7zr+G9gV2lbmSdWEZOGB12jaquOAq6k4XVR3doe4Q= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=armlinux.org.uk; spf=none smtp.mailfrom=armlinux.org.uk; dkim=pass (2048-bit key) header.d=armlinux.org.uk header.i=@armlinux.org.uk header.b=JM4HoprP; arc=none smtp.client-ip=78.32.30.218 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=armlinux.org.uk Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=armlinux.org.uk Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=armlinux.org.uk header.i=@armlinux.org.uk header.b="JM4HoprP" 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> Precedence: bulk X-Mailing-List: netdev@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: <20251126-a10_ext_fix-v1-1-d163507f646f@altera.com> Sender: Russell King (Oracle) 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!