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=-13.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_IN_DEF_DKIM_WL 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 7E4DCC433E0 for ; Tue, 16 Feb 2021 18:50:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4CEAF64E28 for ; Tue, 16 Feb 2021 18:50:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230073AbhBPSuP (ORCPT ); Tue, 16 Feb 2021 13:50:15 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51042 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230210AbhBPSuM (ORCPT ); Tue, 16 Feb 2021 13:50:12 -0500 Received: from mail-yb1-xb36.google.com (mail-yb1-xb36.google.com [IPv6:2607:f8b0:4864:20::b36]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3CF72C06178A for ; Tue, 16 Feb 2021 10:49:07 -0800 (PST) Received: by mail-yb1-xb36.google.com with SMTP id p186so11453921ybg.2 for ; Tue, 16 Feb 2021 10:49:07 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=ulqwXrQZpRrYT3IHT4CJ8bN5l6f9WiL4VvK05t2vkhU=; b=GFVUZyY2+36xaWQOsBNcWeZvX9dgErqzir1orOVD41NTZeSKMP3B4a8JAZpGfpZNzN 7bXyMp1VBKh/kAFxyiGVdzGSA28wFoRfpMTz2roVpux4P7yqn6bWrY2qK82Ppkov5uAu QUDkguqttvIFR+d3KCw1u52ojhCNVVQmY4DxpG/8ts2opf5bn67o4y7luRYhIOq2Pvlw IvqSqfN5YIBG35KA0rfgWvZir4VWpbMA8m7NKzrc+hEQ4W99fQF8YRU4P7ukvmPeARfm S0fkAUw88oh53rPVhsngwpmb43ayPtF8/Jb5qc2PUkdNqhbSgYiCedPXLmVT5cQJ805u S1+w== 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=ulqwXrQZpRrYT3IHT4CJ8bN5l6f9WiL4VvK05t2vkhU=; b=jFogOSz6X9bKfcYeO7uFuXiQhz6dRz6+fDysE4fjlNJMk6CR/lgfCO24xwwc2oNjYg d/8ba+c5bey12ZkOAqibuQcUM6j87+0qh0vRwlEI3m1+PRIYENhwmEl35MIa6jCQYhZg Rfy294R6SwVJ5qfARUVdVW9QBJPeA7+eI7BavLkxI4PxLP3RTo6euMwf5JvOW0TfmKMn bhRhGNmhyYMeC40WYQvJ2dQRyl8uxuP7N1HcaaEQwhyt6CberrnLnpxceyRBrURSRDEe i4oqo0c9Um3RCi3DLs4YTcYQHVfIUtVPI3FtHUnc4EICHbStiMUaUxD6ytxfTP2YW1ox fVBA== X-Gm-Message-State: AOAM532qgblVT+sFDh8DsQ0j5vLRcjdNLfXgM3Txi6lLQlznpD3duB5b ocDd2blLWSifMlVIbcR1/mOa8SE5FrWEjTYS+nkF7w== X-Google-Smtp-Source: ABdhPJy/W97Gt0DiNuOozzUVmxZ1k867IJaF8h5dqBDAKdPQOmZJZO6WvC505FeNpD/Kj6p1JVZxSHxHAj6xXqAAWDU= X-Received: by 2002:a05:6902:1025:: with SMTP id x5mr31500894ybt.96.1613501346147; Tue, 16 Feb 2021 10:49:06 -0800 (PST) MIME-Version: 1.0 References: <20210205222644.2357303-1-saravanak@google.com> In-Reply-To: From: Saravana Kannan Date: Tue, 16 Feb 2021 10:48:30 -0800 Message-ID: Subject: Re: [PATCH v4 0/8] Make fw_devlink=on more forgiving To: Geert Uytterhoeven 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-doc@vger.kernel.org On Tue, Feb 16, 2021 at 12:05 AM Geert Uytterhoeven wrote: > > 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? No, I didn't do that in case the drivers that didn't need the IOMMU/DMA were sensitive to probe order. My goal was for fw_devlink=on to not affect probe order for devices that currently don't need to defer probe. But see below... > > > > > > 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. Can you explain more please? This below makes it sound like DMA just sneaks in at the last minute. > > > 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. > fw_devlinks calling driver_deferred_probe_add() > on all consumers has a big impact on probe order. Ugh... yeah. That's the real issue. This is really a device links issue that fw_devlink is exposing. I already have a bunch of things in my TODO list to improve deferred probing and probe ordering. Since this is not causing boot issues (only DMA issue) with fw_devlink=on, can we treat this as not a blocking item for fw_devlink=on? Once I go through my TODO list, it should be fixed (by not changing probe ordering unnecessarily). And if not, I can help find out a different solution at that point. Also, if you have IOMMU drivers, then fw_devlink.strict is also another solution that's available. On a separate note (not a final fix), I was wondering if we should have a config for fw_devlink.strict default value and then have it selected when IOMMU drivers configs are enabled. -Saravana