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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 877AEC33CAD for ; Tue, 14 Jan 2020 07:21:18 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 5CD542084D for ; Tue, 14 Jan 2020 07:21:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="FBLmig+X" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5CD542084D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=chromium.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=dri-devel-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id CA5116E2CC; Tue, 14 Jan 2020 07:21:17 +0000 (UTC) Received: from mail-qt1-x841.google.com (mail-qt1-x841.google.com [IPv6:2607:f8b0:4864:20::841]) by gabe.freedesktop.org (Postfix) with ESMTPS id 96E636E2CC for ; Tue, 14 Jan 2020 07:21:16 +0000 (UTC) Received: by mail-qt1-x841.google.com with SMTP id c24so831513qtp.5 for ; Mon, 13 Jan 2020 23:21:16 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=Qu8L9/P7G3E9Yw4p+SvLP/VGjTn+xJR8yruIENAwmw8=; b=FBLmig+XuYQLjy+MeDi4VsXucyJ6x0+XdvVzpi5nWJqWnehAgKtDnYacLVqKcbPzIH UyGqW0OT0p1dWpNDMovF2Lm9I6w7iFZU/8ULTFeHFJQ9p5LA9Zgyc+J1gC6Hyp8txp+1 vMsvum9BkFPYlPeoCokHaWZR/Gb75cRTzLyB4= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=Qu8L9/P7G3E9Yw4p+SvLP/VGjTn+xJR8yruIENAwmw8=; b=j3/5jlNWy6xbGOOStp4ZELNADK6QEiXmdRYr8gj67YvnSg9Shus7fmHk71pfNLHoK8 3KcH4F1FyJlm03CgBAx8ACykxBZXY6maQfL6qUAJQDkq1VAIa6/VA8L6C08eDSkm52Hh snIbcZ/wxR1aPaVzSD9F0ZYrgBkLnb7gEfhEHqSDYPv9L0bEoNYp12HhIPW+M+Wmc0GY /eFpB3yu4/LUsTpYXc2i7SDIQ77K/mq87vM+en65aq5J9YsEXJMIQVXTVljk007P8fv8 y/LKKFHo3rK/JrfMkDdmplrHkGB+bPKUBza/dgu8Y81W8RQ/ORUoqUPO7cOxh5UjZ/5E JjNw== X-Gm-Message-State: APjAAAVmmxxySwBpfRDLfIjRHSHcPa0dODmyjZAQcv7O3RWzvGypqUGP 4QXLNYrBSIe0KfDLpyIZ+9kIfHbn6cz9ZekWBA3dig== X-Google-Smtp-Source: APXvYqy5dTRwvBZSp2Sl2oa5uqtPjgwo9dLYORqfUzS4GprMz5UdJxHfSaILw3N4vb/BqqZHf3UJ8KY/Bw2G5cK4+Kc= X-Received: by 2002:ac8:4446:: with SMTP id m6mr2448249qtn.159.1578986475520; Mon, 13 Jan 2020 23:21:15 -0800 (PST) MIME-Version: 1.0 References: <20200108052337.65916-1-drinkcat@chromium.org> <20200108052337.65916-5-drinkcat@chromium.org> <20200108132302.GA3817@sirena.org.uk> <09ddfac3-da8d-c039-92a0-d0f51dc3fea5@arm.com> <20200109162814.GB3702@sirena.org.uk> <20200109194930.GD3702@sirena.org.uk> <90993401-6896-bf95-a15a-d99c465ec12a@arm.com> In-Reply-To: <90993401-6896-bf95-a15a-d99c465ec12a@arm.com> From: Nicolas Boichat Date: Tue, 14 Jan 2020 15:21:04 +0800 Message-ID: Subject: Re: [PATCH v2 4/7] drm/panfrost: Add support for a second regulator for the GPU To: Steven Price X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Devicetree List , Tomeu Vizoso , David Airlie , lkml , dri-devel , Liam Girdwood , Rob Herring , Mark Brown , "moderated list:ARM/Mediatek SoC support" , Alyssa Rosenzweig , Hsin-Yi Wang , Matthias Brugger , linux-arm Mailing List Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Fri, Jan 10, 2020 at 7:30 PM Steven Price wrote: > > On 09/01/2020 19:49, Mark Brown wrote: > > On Thu, Jan 09, 2020 at 04:53:02PM +0000, Steven Price wrote: > >> On 09/01/2020 16:28, Mark Brown wrote: > >>> On Thu, Jan 09, 2020 at 02:14:42PM +0000, Steven Price wrote: > > > >>>> I'm not sure if it's better, but could we just encode the list of > >>>> regulators into device tree. I'm a bit worried about special casing an > >>>> "sram" regulator given that other platforms might have a similar > >>>> situation but call the second regulator a different name. > > > >>> Obviously the list of regulators bound on a given platform is encoded in > >>> the device tree but you shouldn't really be relying on that to figure > >>> out what to request in the driver - the driver should know what it's > >>> expecting. > > > >> From a driver perspective we don't expect to have to worry about power > >> domains/multiple regulators - the hardware provides a bunch of power > >> registers to turn on/off various parts of the hardware and this should be > >> linked (in hardware) to a PDC which sorts it out. The GPU/PDC handles the > >> required sequencing. So it *should* be a case of turn power/clocks on and > >> go. > > > > Ah, the well abstracted and consistent hardware with which we are all so > > fortunate to work :) . More seriously perhaps the thing to do here is > > create a driver that provides a soft PDC and then push all the special > > case handling into that? It can then get instantiated based on the > > compatible or perhaps represented directly in the device tree if that > > makes sense. > > That makes sense to me. > > >> However certain integrations may have quirks such that there are physically > >> multiple supplies. These are expected to all be turned on before using the > >> GPU. Quite how this is best represented is something I'm not sure about. > > > > If they're always on and don't ever change then that's really easy to > > represent in the DT without involving drivers, it's when you need to > > actively manage them that it's more effort. > > Sorry, I should have been more clear. They are managed as a group - so > either the entire GPU is powered off, or powered on. There's no support > in Panfrost or mali_kbase for attempting to power part of the GPU. > > >>> Bear in mind that getting regulator stuff wrong can result > >>> in physical damage to the system so it pays to be careful and to > >>> consider that platform integrators have a tendency to rely on things > >>> that just happen to work but aren't a good idea or accurate > >>> representations of the system. It's certainly *possible* to do > >>> something like that, the information is there, but I would not in any > >>> way recommend doing things that way as it's likely to not be robust. > > > >>> The possibility that the regulator setup may vary on other platforms > >>> (which I'd expect TBH) does suggest that just requesting a bunch of > >>> supply names optionally and hoping that we got all the ones that are > >>> important on a given platform is going to lead to trouble down the line. > > > >> Certainly if we miss a regulator the GPU isn't going to work properly (some > >> cores won't be able to power up successfully). However at the moment the > >> driver will happily do this if someone provides it with a DT which includes > >> regulators that it doesn't know about. So I'm not sure how adding special > >> case code for a SoC would help here. > > > > I thought this SoC neeed to vary the voltage on both rails as part of > > the power management? Things like that can lead to hardware damage if > > we go out of spec far enough for long enough - there can be requirements > > like keeping one rail a certain voltage above another or whatever. > > Yes, you are correct. My concern is that a DT which specifies a new > regulator (e.g. "sram2") would be accepted by an old kernel (because it > wouldn't know to look for the new regulator) but wouldn't know to > control the regulator. It could then create a situation which puts the > board out of spec - potentially in a damaging way. Hence I'd like to > express the regulator structure in such a way that old kernels wouldn't > "half-work". Your "soft-PDC" approach would seem to fit that requirement. FYI, I sent a v3 here: https://patchwork.kernel.org/patch/11331373/ that addresses _some_ of these concerns. I'm not quite sure how to describe the regulators in a way that we can check that the device tree does not specific extra ones (apart from doing some string matching on all properties?), and I don't think I'm best placed to implement the soft-PDC idea. See my comment on that patch. Thanks! _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel