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 X-Spam-Level: X-Spam-Status: No, score=-3.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D5FE2C433E7 for ; Fri, 9 Oct 2020 08:36:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 70B5D22269 for ; Fri, 9 Oct 2020 08:36:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732710AbgJIIgI (ORCPT ); Fri, 9 Oct 2020 04:36:08 -0400 Received: from mx2.suse.de ([195.135.220.15]:58156 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732613AbgJIIgI (ORCPT ); Fri, 9 Oct 2020 04:36:08 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 2F7D6AC7D; Fri, 9 Oct 2020 08:36:06 +0000 (UTC) Message-ID: <513833810c15b5efeab7c3cbae1963a78c71a79f.camel@suse.de> Subject: Re: [PATCH 1/4] of/fdt: Update zone_dma_bits when running in bcm2711 From: Nicolas Saenz Julienne To: Ard Biesheuvel , Christoph Hellwig Cc: "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , Frank Rowand , Catalin Marinas , Linux Kernel Mailing List , Linux Memory Management List , iommu@lists.linux-foundation.org, Rob Herring , linux-rpi-kernel@lists.infradead.org, Will Deacon , Linux ARM , Robin Murphy Date: Fri, 09 Oct 2020 10:36:02 +0200 In-Reply-To: References: <20201001161740.29064-1-nsaenzjulienne@suse.de> <20201001161740.29064-2-nsaenzjulienne@suse.de> <20201001171500.GN21544@gaia> <20201001172320.GQ21544@gaia> <20201002115541.GC7034@gaia> <12f33d487eabd626db4c07ded5a1447795eed355.camel@suse.de> <20201009071013.GA12208@lst.de> Content-Type: multipart/signed; micalg="pgp-sha256"; protocol="application/pgp-signature"; boundary="=-HZps7YTW5opz4O9P41Ik" User-Agent: Evolution 3.36.5 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org --=-HZps7YTW5opz4O9P41Ik Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Fri, 2020-10-09 at 09:37 +0200, Ard Biesheuvel wrote: > On Fri, 9 Oct 2020 at 09:11, Christoph Hellwig wrote: > > On Thu, Oct 08, 2020 at 12:05:25PM +0200, Nicolas Saenz Julienne wrote: > > > Sadly I just realised that the series is incomplete, we have RPi4 use= rs that > > > want to boot unsing ACPI, and this series would break things for them= . I'll > > > have a word with them to see what we can do for their use-case. > >=20 > > Stupid question: why do these users insist on a totally unsuitable > > interface? And why would we as Linux developers care to support such > > a aims? > > The point is really whether we want to revert changes in Linux that > made both DT and ACPI boot work without quirks on RPi4. Well, and broke a big amount of devices that were otherwise fine. > Having to check the RPi4 compatible string or OEM id in core init code is > awful, regardless of whether you boot via ACPI or via DT. > > The problem with this hardware is that it uses a DMA mask which is > narrower than 32, and the arm64 kernel is simply not set up to deal > with that at all. On DT, we have DMA ranges properties and the likes > to describe such limitations, on ACPI we have _DMA methods as well as > DMA range attributes in the IORT, both of which are now handled > correctly. So all the information is there, we just have to figure out > how to consume it early on. Is it worth the effort just for a single board? I don't know about ACPI but parsing dma-ranges that early at boot time is not trivial. My intuition tel= ls me that it'd be even harder for ACPI, being a more complex data structure. > Interestingly, this limitation always existed in the SoC, but it > wasn't until they started shipping it with more than 1 GB of DRAM that > it became a problem. This means issues like this could resurface in > the future with existing SoCs when they get shipped with more memory, > and so I would prefer fixing this in a generic way. Actually what I proposed here is pretty generic. Specially from arm64's perspective. We call early_init_dt_scan(), which sets up zone_dma_bits base= d on whatever it finds in DT. Both those operations are architecture independent= . arm64 arch code doesn't care about the logic involved in ascertaining zone_dma_bits. I get that the last step isn't generic. But it's all setup s= o as to make it as such whenever it's worth the effort. > Also, I assume papering over the issue like this does not fix the > kdump issue fundamentally, it just works around it, and so we might > run into this again in the future. Any ideas? The way I understand it the kdump issue is just a shortcoming of the memory zones design. Regards, Nicolas --=-HZps7YTW5opz4O9P41Ik Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- iQEzBAABCAAdFiEErOkkGDHCg2EbPcGjlfZmHno8x/4FAl+AIPIACgkQlfZmHno8 x/7ixwgArMPUc2i51aFQ1Vewm9MoFEcZuXJtOXO+kufsCRa58yp7GAAVBhH6IBHb QfxFIDcQrHnSeOcYjCYeFjT1fH8Hg0NusddHoN+1A0dcFJltSmn6We+abDhmHj8M xtBmhNjGmlvNqZrJdhqqhvT421GIj0cSZZX9ZVfGmFVLb8ALsmRiNaNAzmhkitzI QMcbZEoCn9M76MC+EsRI6pwpTQsXkuN3XWKqNE8hXVtqXQEBkGqZgZcc6I3OY4MX mj6kolVLJ/mr785/1E/8qehLDT6J1lg/lH0G6GtMCBagDRfU4cKj/LXr8L/UXtIm lRJY0eAY18TiA9o655u+JyGxXFqeuQ== =shiA -----END PGP SIGNATURE----- --=-HZps7YTW5opz4O9P41Ik--