From nobody Sun Feb 8 15:23:11 2026 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DFD47C4332F for ; Wed, 8 Nov 2023 17:39:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231567AbjKHRjU (ORCPT ); Wed, 8 Nov 2023 12:39:20 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45816 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229907AbjKHRjT (ORCPT ); Wed, 8 Nov 2023 12:39:19 -0500 X-Greylist: delayed 509 seconds by postgrey-1.37 at lindbergh.monkeyblade.net; Wed, 08 Nov 2023 09:39:15 PST Received: from mail.tkos.co.il (wiki.tkos.co.il [84.110.109.230]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 76E3F1FF9 for ; Wed, 8 Nov 2023 09:39:15 -0800 (PST) Received: from tarshish.tkos.co.il (unknown [10.0.8.3]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.tkos.co.il (Postfix) with ESMTPS id CA51A440F61; Wed, 8 Nov 2023 19:29:47 +0200 (IST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=tkos.co.il; s=default; t=1699464587; bh=1yLvpECl2rEGKsiM0fBZ4N89l8tkzdS1xWi8lB8tcnY=; h=From:To:Cc:Subject:Date:From; b=WYZBm2Gg+ekQkqyy3/yQwk9KwZsuYzf7EPGZgq25AcBtEiQYIG9v79dlW0g7MFcOU Hh8ySGKTW3Fx0e3dCwYbkJIkzEE4adqj/fzuCKT6GF6OWXm5uPMvAOpJtDD/+GPcv3 l3JXWD2sDN+i+jAFXUMtdp9R2vXm+qZ9eEzNs6WN2Gi88tDjetYxnUe7poiIGEBB6c MKEPDl4oIEyrXJgKK2MLlbgsWvSW0CQgDmaorWljdQfs+XGTfY+Y+ngeQyBxp060jM 1UCzfy+cvy/JAkUjz81Nh1WfRBeb6B4pbjZJxgOgfyk3LPy+rok4L6pCKOXEC5OQDs HnR/oqxVyIfRA== From: Baruch Siach To: Catalin Marinas , Will Deacon Cc: Christoph Hellwig , Marek Szyprowski , Robin Murphy , Ramon Fried , iommu@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Baruch Siach Subject: [PATCH RFC] arm64: DMA zone above 4GB Date: Wed, 8 Nov 2023 19:30:22 +0200 Message-ID: <9af8a19c3398e7dc09cfc1fbafed98d795d9f83e.1699464622.git.baruch@tkos.co.il> X-Mailer: git-send-email 2.42.0 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" My platform RAM starts at 32GB. It has no RAM under 4GB. zone_sizes_init() puts the entire RAM in the DMA zone as follows: [ 0.000000] Zone ranges: [ 0.000000] DMA [mem 0x0000000800000000-0x00000008bfffffff] [ 0.000000] DMA32 empty [ 0.000000] Normal empty Consider a bus with this 'dma-ranges' property: #address-cells =3D <2>; #size-cells =3D <2>; dma-ranges =3D <0x00000000 0xc0000000 0x00000008 0x00000000 0x0 0x4000000= 0>; Devices under this bus can see 1GB of DMA range between 3GB-4GB. This range is mapped to CPU memory at 32GB-33GB. Current zone_sizes_init() code considers 'dma-ranges' only when it maps to RAM under 4GB, because zone_dma_bits is limited to 32. In this case 'dma-ranges' is ignored in practice, since DMA/DMA32 zones are both assumed to be located under 4GB. The result is that the stmmac driver DMA buffers allocation GFP_DMA32 flag has no effect. As a result DMA buffer allocations fail. The patch below is a crude workaround hack. It makes the DMA zone cover the 1GB memory area that is visible to stmmac DMA as follows: [ 0.000000] Zone ranges: [ 0.000000] DMA [mem 0x0000000800000000-0x000000083fffffff] [ 0.000000] DMA32 empty [ 0.000000] Normal [mem 0x0000000840000000-0x0000000bffffffff] ... [ 0.000000] software IO TLB: mapped [mem 0x000000083bfff000-0x000000083f= fff000] (64MB) With this hack the stmmac driver works on my platform with no modification. Clearly this can't be the right solutions. zone_dma_bits is now wrong for one. It probably breaks other code as well. Is there any better suggestion to make DMA buffer allocations work on this hardware? Thanks --- arch/arm64/mm/init.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c index 74c1db8ce271..5fe826ac3a5f 100644 --- a/arch/arm64/mm/init.c +++ b/arch/arm64/mm/init.c @@ -136,13 +136,13 @@ static void __init zone_sizes_init(void) unsigned long max_zone_pfns[MAX_NR_ZONES] =3D {0}; unsigned int __maybe_unused acpi_zone_dma_bits; unsigned int __maybe_unused dt_zone_dma_bits; - phys_addr_t __maybe_unused dma32_phys_limit =3D max_zone_phys(32); + phys_addr_t __maybe_unused dma32_phys_limit =3D DMA_BIT_MASK(32) + 1; =20 #ifdef CONFIG_ZONE_DMA acpi_zone_dma_bits =3D fls64(acpi_iort_dma_get_max_cpu_address()); dt_zone_dma_bits =3D fls64(of_dma_get_max_cpu_address(NULL)); zone_dma_bits =3D min3(32U, dt_zone_dma_bits, acpi_zone_dma_bits); - arm64_dma_phys_limit =3D max_zone_phys(zone_dma_bits); + arm64_dma_phys_limit =3D of_dma_get_max_cpu_address(NULL) + 1; max_zone_pfns[ZONE_DMA] =3D PFN_DOWN(arm64_dma_phys_limit); #endif #ifdef CONFIG_ZONE_DMA32 --=20 2.42.0