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Mon, 15 Jun 2020 15:42:43 -0400 Received: from mail-pl1-x641.google.com (mail-pl1-x641.google.com [IPv6:2607:f8b0:4864:20::641]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C0286C08C5C2 for ; Mon, 15 Jun 2020 12:42:42 -0700 (PDT) Received: by mail-pl1-x641.google.com with SMTP id y18so7226511plr.4 for ; Mon, 15 Jun 2020 12:42:42 -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:in-reply-to; bh=tNVFiaYWMiO2hIPSPELA+UbwGrUr+c9/QS6tPzZlZsA=; b=Q1gomGsuoZPi4npsUFWHj1X8MZjjMEubXg7JRHxvk16FoLBYMBUvqQMm982CkHMfju kTVQPbwC0DsOCx0LE6fgPtUKSTAeU8r5AWd12DkRI0M02V8Z+b+P4J2xJcfSFVf8Wchh 6A31hSMp5TIxadWGu7+0uTJE0uXGGueo9vk6M= 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:in-reply-to; bh=tNVFiaYWMiO2hIPSPELA+UbwGrUr+c9/QS6tPzZlZsA=; 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charset=utf-8 Content-Disposition: inline In-Reply-To: <159126939154.69627.13027312816468830595@swboyd.mtv.corp.google.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.