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=-3.8 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 3170AC433E0 for ; Tue, 16 Feb 2021 08:06:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D403F64D9E for ; Tue, 16 Feb 2021 08:06:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229710AbhBPIGW (ORCPT ); Tue, 16 Feb 2021 03:06:22 -0500 Received: from mail-oi1-f173.google.com ([209.85.167.173]:41934 "EHLO mail-oi1-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229635AbhBPIGV (ORCPT ); Tue, 16 Feb 2021 03:06:21 -0500 Received: by mail-oi1-f173.google.com with SMTP id v193so10377161oie.8; Tue, 16 Feb 2021 00:06:05 -0800 (PST) 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=83BrpC0oQ/cmeAj/lHKeDzK9StSyqlfuwywAdDjNejw=; b=QBgBUBqgx1FN/5KM3VfFOpGjnuJqRT6RfKbqnFNNIUKXAxvOKKb6hhQNp6UoY2//d9 gH9b4zjKmunB8jgDTzJnHj5UkJ22QmdHCTgfoV4ubdn3MknMyfMZNmfTcLgyCH/mVZwz wDgFAs0Uc89WRqE84ReBUia2b1YfWdQ2dHnmDfUbtXn2i71MQcgPyPEGmFwE09AwbpVn moQ3RkGaBjggWRWfEZUeGiRSoqyPP2qKIVBAhFnOGtuIr4RvvBhVgSjpT84b5B0GXUXE 5e8BdVdVAxcJMt/Cz526LpfeyJA9AwH96YbaSfigvhtbwTe9Ql5Qa1RrBlepYly2ILPF PKww== X-Gm-Message-State: AOAM533sr8FRE/LxLo2YI9f/zHqLnNj/hkQmACmwQPh1dC/tDUXsPSnY zIyAN8KUIYNJ+vE+mSXdU8J2RS8R4Or1uz5LcrA= X-Google-Smtp-Source: ABdhPJzz+NpULZTIa3tjUW8686AiYK7eX+4Ie30gH/r1xHcs0vWPfv5qgwYUJGkxQKm1FzqrQsvfEXHLJ4R55M5RltI= X-Received: by 2002:aca:d8c6:: with SMTP id p189mr1857071oig.54.1613462740012; Tue, 16 Feb 2021 00:05:40 -0800 (PST) MIME-Version: 1.0 References: <20210205222644.2357303-1-saravanak@google.com> In-Reply-To: From: Geert Uytterhoeven Date: Tue, 16 Feb 2021 09:05:28 +0100 Message-ID: Subject: Re: [PATCH v4 0/8] Make fw_devlink=on more forgiving To: Saravana Kannan Cc: Jonathan Corbet , Greg Kroah-Hartman , "Rafael J. Wysocki" , Kevin Hilman , Ulf Hansson , Len Brown , Len Brown , Pavel Machek , Michael Turquette , Stephen Boyd , Rob Herring , Frank Rowand , Marc Zyngier , Thomas Gleixner , "open list:DOCUMENTATION" , Linux Kernel Mailing List , Linux PM list , linux-clk , "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , ACPI Devel Maling List , Marek Szyprowski , Android Kernel Team , Linux-Renesas Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-acpi@vger.kernel.org Hi Saravana, On Mon, Feb 15, 2021 at 10:27 PM Saravana Kannan wrote: > On Mon, Feb 15, 2021 at 4:38 AM Geert Uytterhoeven wrote: > > On Fri, Feb 12, 2021 at 4:00 AM Saravana Kannan wrote: > > > On Thu, Feb 11, 2021 at 5:00 AM Geert Uytterhoeven wrote: > > > > - I2C on R-Car Gen3 does not seem to use DMA, according to > > > > /sys/kernel/debug/dmaengine/summary: > > > > > > > > -dma4chan0 | e66d8000.i2c:tx > > > > -dma4chan1 | e66d8000.i2c:rx > > > > -dma5chan0 | e6510000.i2c:tx > > > > > > I think I need more context on the problem before I can try to fix it. > > > I'm also very unfamiliar with that file. With fw_devlink=permissive, > > > I2C was using DMA? If so, the next step is to see if the I2C relative > > > probe order with DMA is getting changed and if so, why. > > > > More detailed log: > > > > platform e66d8000.i2c: Linked as a consumer to e6150000.clock-controller > > platform e66d8000.i2c: Linked as a sync state only consumer to e6055400.gpio > > > > Why is e66d8000.i2c not linked as a consumer to e6700000.dma-controller? > > Because fw_devlink.strict=1 is not set and dma/iommu is considered an > "optional"/"driver decides" dependency. Oh, I thought dma/iommu were considered mandatory initially, but dropped as dependencies in the late boot process? > > > platform e6700000.dma-controller: Linked as a consumer to > > e6150000.clock-controller > > Is this the only supplier of dma-controller? No, e6180000.system-controller is also a supplier. > > platform e66d8000.i2c: Added to deferred list > > platform e6700000.dma-controller: Added to deferred list > > > > bus: 'platform': driver_probe_device: matched device > > e6700000.dma-controller with driver rcar-dmac > > bus: 'platform': really_probe: probing driver rcar-dmac with > > device e6700000.dma-controller > > platform e6700000.dma-controller: Driver rcar-dmac requests probe deferral > > > > bus: 'platform': driver_probe_device: matched device e66d8000.i2c > > with driver i2c-rcar > > bus: 'platform': really_probe: probing driver i2c-rcar with device > > e66d8000.i2c > > > > I2C becomes available... > > > > i2c-rcar e66d8000.i2c: request_channel failed for tx (-517) > > [...] > > > > but DMA is not available yet, so the driver falls back to PIO. > > > > driver: 'i2c-rcar': driver_bound: bound to device 'e66d8000.i2c' > > bus: 'platform': really_probe: bound device e66d8000.i2c to driver i2c-rcar > > > > platform e6700000.dma-controller: Retrying from deferred list > > bus: 'platform': driver_probe_device: matched device > > e6700000.dma-controller with driver rcar-dmac > > bus: 'platform': really_probe: probing driver rcar-dmac with > > device e6700000.dma-controller > > platform e6700000.dma-controller: Driver rcar-dmac requests probe deferral > > platform e6700000.dma-controller: Added to deferred list > > platform e6700000.dma-controller: Retrying from deferred list > > bus: 'platform': driver_probe_device: matched device > > e6700000.dma-controller with driver rcar-dmac > > bus: 'platform': really_probe: probing driver rcar-dmac with > > device e6700000.dma-controller > > driver: 'rcar-dmac': driver_bound: bound to device 'e6700000.dma-controller' > > bus: 'platform': really_probe: bound device > > e6700000.dma-controller to driver rcar-dmac > > > > DMA becomes available. > > > > Here userspace is entered. /sys/kernel/debug/dmaengine/summary shows > > that the I2C controllers do not have DMA channels allocated, as the > > kernel has performed no more I2C transfers after DMA became available. > > > > Using i2cdetect shows that DMA is used, which is good: > > > > i2c-rcar e66d8000.i2c: got DMA channel for rx > > > > With permissive devlinks, the clock controller consumers are not added > > to the deferred probing list, and probe order is slightly different. > > The I2C controllers are still probed before the DMA controllers. > > But DMA becomes available a bit earlier, before the probing of the last > > I2C slave driver. > > This seems like a race? I'm guessing it's two different threads > probing those two devices? And it just happens to work for > "permissive" assuming the boot timing doesn't change? > > > Hence /sys/kernel/debug/dmaengine/summary shows that > > some I2C transfers did use DMA. > > > > So the real issue is that e66d8000.i2c not linked as a consumer to > > e6700000.dma-controller. > > That's because fw_devlink.strict=1 isn't set. If you need DMA to be > treated as a mandatory supplier, you'll need to set the flag. > > Is fw_devlink=on really breaking anything here? It just seems like > "permissive" got lucky with the timing and it could break at any point > in the future. Thought? I don't think there is a race. fw_devlinks calling driver_deferred_probe_add() on all consumers has a big impact on probe order. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds