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=-3.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, 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 AA0CEC433DF for ; Tue, 16 Jun 2020 20:38:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7C73820776 for ; Tue, 16 Jun 2020 20:38:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="KfKVNYLi" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729860AbgFPUiw (ORCPT ); Tue, 16 Jun 2020 16:38:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35386 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729648AbgFPUiw (ORCPT ); Tue, 16 Jun 2020 16:38:52 -0400 Received: from mail-pj1-x1041.google.com (mail-pj1-x1041.google.com [IPv6:2607:f8b0:4864:20::1041]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 79069C061573 for ; Tue, 16 Jun 2020 13:38:51 -0700 (PDT) Received: by mail-pj1-x1041.google.com with SMTP id s88so2167916pjb.5 for ; Tue, 16 Jun 2020 13:38:51 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:content-transfer-encoding:in-reply-to; bh=wpW7WQOPePDKMe4iZDKX0l11TokFWfmINzOLwuMIeCc=; b=KfKVNYLiedCg1CnE06VLMC/PwK175OV5P5PHufSzCNh0nJ7KEXIUIU4wZkS/KMerT0 AbGvvBi0Yh6Yrxp20lOX+VF9h0OFkiXx2H7Xd1XbC6EX2nRfu36kfoVOpqEKG1vXwVl8 uKWii7dd1i8zzTsxssgv8F7xVl/wDR61ycV7k= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:content-transfer-encoding :in-reply-to; bh=wpW7WQOPePDKMe4iZDKX0l11TokFWfmINzOLwuMIeCc=; b=lcbO52MKO0KQStMHj/fYOnwJBzuJfHS6l9dm76ryf4PVv9qJi+TQhSVG05HrX6T/my XGQ9Dtk9QLSoNvjTRVBNaIj09M2QiUpYvyWm2INjfuNyTtANNoTPOXpCMdxnms8z/nwX 7VHw+XU448IkRxyAWxgVml8PGaJdJ9p3Rd9XsnmGz+798m8bIQ5/HVtxOoCSbfl0JFgN Vhuv+47a9TL7t4RYQkK8ILyHcEmzXnJsvilBgJDHWJhwBrQoZHrY+c8WkZ4a6bxwofLR FTl3MuGGxBa1vviSZs0Gyab65GWrUZE/2jtZLCx2q92TRjfU+99YsyigJEaCg0S05d/T pkOQ== X-Gm-Message-State: AOAM533+TlYpXpReyKKAFwJKFiQSnmlM/qtMgN1gyGTELwnLtvXq/ghT WBzAiILvUA0HFeJFoHjbqNFrQQ== X-Google-Smtp-Source: ABdhPJwY/p64B3ltGSHrZiAknPCYjQKtsT/wlseuFxUfBLRtgL2hch0z3uFzCPdDbvEx7sCnip96AQ== X-Received: by 2002:a17:902:9f90:: with SMTP id g16mr3672533plq.146.1592339930938; Tue, 16 Jun 2020 13:38:50 -0700 (PDT) Received: from localhost ([2620:15c:202:1:4fff:7a6b:a335:8fde]) by smtp.gmail.com with ESMTPSA id t22sm3187788pjy.32.2020.06.16.13.38.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 16 Jun 2020 13:38:50 -0700 (PDT) Date: Tue, 16 Jun 2020 13:38:49 -0700 From: Matthias Kaehlcke To: "Sandeep Maheswaram (Temp)" Cc: Stephen Boyd , Andy Gross , Bjorn Andersson , Doug Anderson , Felipe Balbi , Greg Kroah-Hartman , Mark Rutland , Rob Herring , linux-arm-msm@vger.kernel.org, linux-usb@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, Manu Gautam , Chandana Kishori Chiluveru Subject: Re: [PATCH v7 2/4] usb: dwc3: qcom: Add interconnect support in dwc3 driver Message-ID: <20200616203849.GY4525@google.com> References: <1585718145-29537-1-git-send-email-sanm@codeaurora.org> <1585718145-29537-3-git-send-email-sanm@codeaurora.org> <159120577830.69627.13288547914742515702@swboyd.mtv.corp.google.com> <159126939154.69627.13027312816468830595@swboyd.mtv.corp.google.com> <20200615194239.GW4525@google.com> <3f8fcb0e-387d-e902-9f6b-1fde9d6ae404@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <3f8fcb0e-387d-e902-9f6b-1fde9d6ae404@codeaurora.org> Sender: linux-arm-msm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-arm-msm@vger.kernel.org On Tue, Jun 16, 2020 at 10:22:47AM +0530, Sandeep Maheswaram (Temp) wrote: > > On 6/16/2020 1:12 AM, Matthias Kaehlcke wrote: > > On Thu, Jun 04, 2020 at 04:16:31AM -0700, Stephen Boyd wrote: > > > Quoting Sandeep Maheswaram (Temp) (2020-06-04 02:43:09) > > > > On 6/3/2020 11:06 PM, Stephen Boyd wrote: > > > > > Quoting Sandeep Maheswaram (2020-03-31 22:15:43) > > > > > > diff --git a/drivers/usb/dwc3/dwc3-qcom.c b/drivers/usb/dwc3/dwc3-qcom.c > > > > > > index 1dfd024..d33ae86 100644 > > > > > > --- a/drivers/usb/dwc3/dwc3-qcom.c > > > > > > +++ b/drivers/usb/dwc3/dwc3-qcom.c > > > > > > @@ -285,6 +307,101 @@ static int dwc3_qcom_resume(struct dwc3_qcom *qcom) > > > > > > return 0; > > > > > > } > > > > > > + > > > > > > +/** > > > > > > + * dwc3_qcom_interconnect_init() - Get interconnect path handles > > > > > > + * @qcom: Pointer to the concerned usb core. > > > > > > + * > > > > > > + */ > > > > > > +static int dwc3_qcom_interconnect_init(struct dwc3_qcom *qcom) > > > > > > +{ > > > > > > + struct device *dev = qcom->dev; > > > > > > + int ret; > > > > > > + > > > > > > + if (!device_is_bound(&qcom->dwc3->dev)) > > > > > > + return -EPROBE_DEFER; > > > > > How is this supposed to work? I see that this was added in an earlier > > > > > revision of this patch series but there isn't any mention of why > > > > > device_is_bound() is used here. It would be great if there was a comment > > > > > detailing why this is necessary. It sounds like maximum_speed is > > > > > important? > > > > > > > > > > Furthermore, dwc3_qcom_interconnect_init() is called by > > > > > dwc3_qcom_probe() which is the function that registers the device for > > > > > qcom->dwc3->dev. If that device doesn't probe between the time it is > > > > > registered by dwc3_qcom_probe() and this function is called then we'll > > > > > fail dwc3_qcom_probe() with -EPROBE_DEFER. And that will remove the > > > > > qcom->dwc3->dev device from the platform bus because we call > > > > > of_platform_depopulate() on the error path of dwc3_qcom_probe(). > > > > > > > > > > So isn't this whole thing racy and can potentially lead us to a driver > > > > > probe loop where the wrapper (dwc3_qcom) and the core (dwc3) are probing > > > > > and we're trying to time it just right so that driver for dwc3 binds > > > > > before we setup interconnects? I don't know if dwc3 can communicate to > > > > > the wrapper but that would be more of a direct way to do this. Or maybe > > > > > the wrapper should try to read the DT property for maximum speed and > > > > > fallback to a worst case high bandwidth value if it can't figure it out > > > > > itself without help from dwc3 core. > > > > > > > > > This was added in V4 to address comments from Matthias in V3 > > > > > > > > https://patchwork.kernel.org/patch/11148587/ > > > > > > > Yes, that why I said: > > > > > > "I see that this was added in an earlier > > > revision of this patch series but there isn't any mention of why > > > device_is_bound() is used here. It would be great if there was a comment > > > detailing why this is necessary. It sounds like maximum_speed is > > > important?" > > > > > > Can you please respond to the rest of my email? > > I agree with Stephen that using device_is_bound() isn't a good option > > in this case, when I suggested it I wasn't looking at the big picture > > of how probing the core driver is triggered, sorry about that. > > > > Reading the speed from the DT with usb_get_maximum_speed() as Stephen > > suggests would be an option, the inconvenient is that we then > > essentially require the property to be defined, while the core driver > > gets a suitable value from hardware registers. Not sure if the wrapper > > driver could read from the same registers. > > > > One option could be to poll device_is_bound() for 100 ms (or so), with > > sleeps between polls. It's not elegant but would probably work if we > > don't find a better solution. > if (np) >         ret = dwc3_qcom_of_register_core(pdev); >     else >         ret = dwc3_qcom_acpi_register_core(pdev); > >     if (ret) { >         dev_err(dev, "failed to register DWC3 Core, err=%d\n", ret); >         goto depopulate; >     } > >     ret = dwc3_qcom_interconnect_init(qcom); >     if (ret) >         goto depopulate; > >     qcom->mode = usb_get_dr_mode(&qcom->dwc3->dev); > > Before calling dwc3_qcom_interconnect_init we are checking > >     if (ret) { >         dev_err(dev, "failed to register DWC3 Core, err=%d\n", ret); >         goto depopulate; >     } > > Doesn't  this condition confirm the core driver is probed? Not really: // called under the hood by of_platform_populate() static int really_probe(struct device *dev, struct device_driver *drv) { ... if (dev->bus->probe) { ret = dev->bus->probe(dev); if (ret) goto probe_failed; } else if (drv->probe) { ret = drv->probe(dev); if (ret) goto probe_failed; } ... probe_failed: ... /* * Ignore errors returned by ->probe so that the next driver can try * its luck. */ ret = 0; ... return ret; } As a result of_platform_populate() in dwc3_qcom_of_register_core() returns 0 even when probing the device failed: [ 0.244339] dwc3-qcom a6f8800.usb: DBG: populate [ 0.244772] dwc3 a600000.dwc3: DBG: dwc3_probe [ 0.245237] dwc3 a600000.dwc3: DBG: dwc3_probe err: -517 [ 0.245264] dwc3-qcom a6f8800.usb: DBG: populate (done) [ 0.245317] dwc3-qcom a6f8800.usb: DBG: dwc3_qcom_interconnect_init() failed: -517 Probe fails because the interconnect stuff isn't ready yet, otherwise it could access invalid data. A later _populate() is successful and the probing of the core is done synchronously, i.e. after _populate() the core driver is fully initialized: [ 3.898106] dwc3-qcom a6f8800.usb: DBG: populate [ 3.908356] dwc3 a600000.dwc3: DBG: dwc3_probe [ 4.205104] dwc3 a600000.dwc3: DBG: dwc3_probe (done) [ 4.210305] dwc3-qcom a6f8800.usb: DBG: populate (done) The synchronous probing in _populate() suggests that using device_is_bound() would actually be a valid option, either the core device was successfully probed or not, there should be no race. I sent a patch that adds this check to dwc3_qcom_of_register_core(), which is less confusing and makes clear that the core device is valid unless this function returns an error: https://lore.kernel.org/patchwork/patch/1257279/ It might make sense to add your "driver core:Export the symbol device_is_bound" patch, mine and this one to a single series. Thanks Matthias