From mboxrd@z Thu Jan 1 00:00:00 1970 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.subspace.kernel.org (Postfix) with ESMTPS id AF321400DE8; Mon, 5 Oct 2026 08:39:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.133 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791189581; cv=none; b=joEy5IoNK9sX24VpLxKyRYlsp0os3+Q1sutdJFBFUo8BKKibBrG9cqIYcV0vdJpbmmG1SSIHSK3RvZBP78UslowNGYWDxH3VqximX84O7lQ8Y1s7JrOOiSu8pn2WzYk8SH0KLehyaTZol/19ZdZeYgbFfNSkqUMuF30n1DJcHwI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791189581; c=relaxed/simple; bh=g+Oo6kbYdXpTWrgAqiIP43Ul0a+nwIHetvB/s/2gGs4=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=f5of7RODT8SVQS+oglqx0xpLxAyMYywl4Id2lMtyG4nUKgw8KJUkqldA2pU5x/QmSc6/Y8LaPWMw1vYuRmCTeyPf4nalN0/zpd1FlF+a7gYIRazUjPkYdRkyBEHUkmnHg/lNfK2aS5l0t72vDpwu2sPjXLulv1gz2lT/CrcVgg0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=bombadil.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=Xn1etKoT; arc=none smtp.client-ip=198.137.202.133 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=bombadil.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="Xn1etKoT" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=8YAheal/bOJc18SMan7lnG9SW9YRTAdQQ//1cWA65q0=; b=Xn1etKoT/4y6enwBaTM8hDjAt7 UrW1RCRlTcUMc8P++S3bg2zlJG6tY7lWy4dOhPT5pClu8FhAQMyoSsRiQOVjArO3/u7HdwcPCvNB3 KhQyxVDEq5NXZrbbviFAjhuyeCwfSDG0m89rSgWfCV/gfppJTeREKi+QLPhlit/LlEq1Xq6k8AOBK tpUo+EWb1zLbUpzXc1ne7cEo37CQJ8LLN02BXSCS3mwYQb07WyZm+oLGZUPMdK21US5x1stqn4ks6 bRh/IK8INtSAlClWOEi/65hZyOFoe6Gl9bNgryLImAb9YkbKSr7EvKU1BKhwcXTurDALFMlaJ3+Tl 8Wht0uVQ==; Received: from hch by bombadil.infradead.org with local (Exim 4.99.1 #2 (Red Hat Linux)) id 1xDeEQ-0000000FuGG-0C32; Mon, 05 Oct 2026 08:39:34 +0000 Date: Mon, 5 Oct 2026 01:39:34 -0700 From: Christoph Hellwig To: Imre Kaloz Cc: Thomas Bogendoerfer , linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 21/38] MIPS: SGI-IP27: route XBridge and PIC DMA through the 32-bit window Message-ID: References: Precedence: bulk X-Mailing-List: linux-kernel@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: X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html On Thu, Oct 01, 2026 at 06:11:56PM +0200, Imre Kaloz wrote: > XBridge does not honour the SN0-style 64-bit direct-mapped DMA address: > commands complete but no data moves. PIC moves no data either. Route > both through the 2GB 32-bit window and cap bus_dma_limit at its top, so > SWIOTLB bounces anything above it. PIC is flagged once a following > patch enumerates it. > > Only XBridge (part 0xd002) is flagged; a Bridge (0xc002) behind a Hub > keeps the 64-bit direct map. The 64MB bounce pool comes from node 0 > whenever DRAM passes 2GB, on Hub any multi-node machine. A PIC bus in > PCI-X mode takes the window too; IRIX does not. It's been a while, but IIRC XBridge also support 64-bit direct-mapped DMA addresses, just differently. If you find a late 2.4 or early 2.6 kernel, it comes with an open source copy of the IRIX-style PCI code under arch/ia64/ that also includes the older chips never used on Altix. It might be worth to take a look at that for clues.