linux-kernel - Re: [PATCH] usb: gadget: m66592-udc: Ignore feature requests for EP0

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Message-ID: <cca54de8-db74-4df0-abfa-7275f8f2a8ac@rowland.harvard.edu>
Date: Sun, 29 Jun 2025 09:33:32 -0400
From: Alan Stern <stern@...land.harvard.edu>
To: Seungjin Bae <eeodqql09@...il.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Kyungtae Kim <Kyungtae.Kim@...tmouth.edu>,
	Uwe Kleine-König <u.kleine-koenig@...libre.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: gadget: m66592-udc: Ignore feature requests for EP0

On Sat, Jun 28, 2025 at 10:59:53PM -0400, Seungjin Bae wrote:
> The `set_feature() and clear_feature() functions handle requests to set or clear the ENDPOINT_HALT feature.
> Currently, these requests are processed for any endpoint, including the control endpoint (EP0).
> 
> The ENDPOINT_HALT feature is not defined for control endpoints according to the USB specification 9.4.5.

Actually that's not correct.  What the spec says is:

	It is neither required nor recommended that the Halt feature be 
	implemented for the Default Control Pipe. However, devices may 
	set the Halt feature of the Default Control Pipe in order to 
	reflect a functional error condition. If the feature is set to 
	one, the device will return STALL in the Data and Status stages 
	of each standard request to the pipe except GetStatus(), 
	SetFeature(), and ClearFeature() requests. The device need not 
	return STALL for class-specific and vendor-specific requests.

Thus, it is valid for devices to support the ENDPOINT_HALT feature for 
control endpoints.

Alan Stern