Re: [PATCH 0/3] Implement role-switch notifications from dwc3-drd to dwc3-qcom

From: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
To: Bjorn Andersson <bjorn.andersson@linaro.org>,
	Peter Chen <peter.chen@kernel.org>
Cc: balbi@kernel.org, agross@kernel.org, gregkh@linuxfoundation.org,
	jackp@codeaurora.org, wcheng@codeaurora.org,
	linux-usb@vger.kernel.org, linux-arm-msm@vger.kernel.org
Subject: Re: [PATCH 0/3] Implement role-switch notifications from dwc3-drd to dwc3-qcom
Date: Thu, 8 Jul 2021 11:17:00 +0100	[thread overview]
Message-ID: <de86a2c5-92cf-da0a-8819-2de4c3c88b3f@linaro.org> (raw)
In-Reply-To: <YOZ3CBNTXFTa+fNx@yoga>

On 08/07/2021 04:54, Bjorn Andersson wrote:
> Bryan had a previous patch where the glue layer was notified about role
> switching (iirc) and as soon as we hit a probe deferal in the core
> driver we'd dereference some pointer in the glue layer. I don't find the
> patch right now, but I suspect it might have been caused by the same
> platform_get_drvdata() as we see in qcom_dwc3_resume_irq().

Here

https://lore.kernel.org/linux-usb/20200311191501.8165-7-bryan.odonoghue@linaro.org/

and here

https://lore.kernel.org/linux-usb/20200311191501.8165-8-bryan.odonoghue@linaro.org/

one thing about that I don't think is right now in retrospect is having 
to find a DT connector in the core, meaning it incorrectly assumes you 
have a node named "connector" as a child of dwc3-core

https://lore.kernel.org/linux-usb/158463604559.152100.9219030962819234620@swboyd.mtv.corp.google.com/

Having done some work with TCPM on pm8150b silicon I see what Stephen 
was saying about that

That's one solid reason I like the USB role-switch API - because it gets 
you out of the business of trying to discern from dwc3-qcom if dwc3-core 
has role-switching turned on by iterating through its range of DT nodes 
and looking for a special one named "connector"

The initial and imperfect solution I had for that looked like this

if (dwc3_qcom_find_gpio_usb_connector(qcom->dwc3)) {}

Wesley had another iteration on that that was a little better

https://lore.kernel.org/linux-usb/20201009082843.28503-4-wcheng@codeaurora.org/

+static int dwc3_qcom_connector_check(struct fwnode_handle *fwnode)
+{
+	if (fwnode && (!fwnode_property_match_string(fwnode, "compatible",
+						     "gpio-usb-b-connector") ||
+	    !fwnode_property_match_string(fwnode, "compatible",
+					  "usb-c-connector")))
+		return 1;
+
+	return 0;
+}

All we are really doing there is replicating functionality that the 
role-switch API already provides


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bod