linux-kernel - Re: [PATCH v3] usb: dwc3: core: fix a issue about clear connect state

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Message-ID: <875z6wdq62.fsf@kernel.org>
Date:   Tue, 27 Oct 2020 10:33:09 +0200
From:   Felipe Balbi <balbi@...nel.org>
To:     Dejin Zheng <zhengdejin5@...il.com>, gregkh@...uxfoundation.org,
        linux-usb@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Dejin Zheng <zhengdejin5@...il.com>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>
Subject: Re: [PATCH v3] usb: dwc3: core: fix a issue about clear connect state

Hi,

Dejin Zheng <zhengdejin5@...il.com> writes:
> According to Synopsys Programming Guide chapter 2.2 Register Resets,
> it cannot reset the DCTL register by setting DCTL.CSFTRST for core soft
> reset, if DWC3 controller as a slave device and stay connected with a usb
> host, then, while rebooting linux, it will fail to reinitialize dwc3 as a
> slave device when the DWC3 controller did not power off. because the
> connection status is incorrect, so we also need to clear DCTL.RUN_STOP
> bit for disabling connect when doing core soft reset. There will still
> be other stale configuration in DCTL, so reset the other fields of DCTL
> to the default value 0.

This commit log is a bit hard to understand. When does this problem
actually happen? It seems like it's in the case of, perhaps, kexecing
into a new kernel, is that right?

At the time dwc3_core_soft_reset() is called, the assumption is that
we're starting with a clean core, from power up. If we have stale
configuration from a previous run, we should fix this on the exit
path. Note that if we're reaching probe with pull up connected, we
already have issues elsewhere.

I think this is not the right fix for the problem.

-- 
balbi

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