From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Jeffrey Hugo <jeffrey.l.hugo@gmail.com>
Cc: Andy Gross <agross@kernel.org>,
Bjorn Andersson <bjorn.andersson@linaro.org>,
jslaby@suse.com, MSM <linux-arm-msm@vger.kernel.org>,
linux-serial@vger.kernel.org, lkml <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2] tty: serial: msm_serial: Fix flow control
Date: Mon, 4 Nov 2019 17:41:23 +0100 [thread overview]
Message-ID: <20191104164123.GA2256087@kroah.com> (raw)
In-Reply-To: <CAOCk7Nptm=Cz17FFKKvsgVxXRgJ-m9zK4RKysqhjb4cwPweSXg@mail.gmail.com>
On Sun, Nov 03, 2019 at 02:51:17PM -0700, Jeffrey Hugo wrote:
> On Sat, Oct 26, 2019 at 11:55 PM Andy Gross <agross@kernel.org> wrote:
> >
> > On Mon, Oct 21, 2019 at 08:46:16AM -0700, Jeffrey Hugo wrote:
> > > hci_qca interfaces to the wcn3990 via a uart_dm on the msm8998 mtp and
> > > Lenovo Miix 630 laptop. As part of initializing the wcn3990, hci_qca
> > > disables flow, configures the uart baudrate, and then reenables flow - at
> > > which point an event is expected to be received over the uart from the
> > > wcn3990. It is observed that this event comes after the baudrate change
> > > but before hci_qca re-enables flow. This is unexpected, and is a result of
> > > msm_reset() being broken.
> > >
> > > According to the uart_dm hardware documentation, it is recommended that
> > > automatic hardware flow control be enabled by setting RX_RDY_CTL. Auto
> > > hw flow control will manage RFR based on the configured watermark. When
> > > there is space to receive data, the hw will assert RFR. When the watermark
> > > is hit, the hw will de-assert RFR.
> > >
> > > The hardware documentation indicates that RFR can me manually managed via
> > > CR when RX_RDY_CTL is not set. SET_RFR asserts RFR, and RESET_RFR
> > > de-asserts RFR.
> > >
> > > msm_reset() is broken because after resetting the hardware, it
> > > unconditionally asserts RFR via SET_RFR. This enables flow regardless of
> > > the current configuration, and would undo a previous flow disable
> > > operation. It should instead de-assert RFR via RESET_RFR to block flow
> > > until the hardware is reconfigured. msm_serial should rely on the client
> > > to specify that flow should be enabled, either via mctrl() or the termios
> > > structure, and only assert RFR in response to those triggers.
> > >
> > > Fixes: 04896a77a97b ("msm_serial: serial driver for MSM7K onboard serial peripheral.")
> > > Signed-off-by: Jeffrey Hugo <jeffrey.l.hugo@gmail.com>
> > > ---
> >
> > Reviewed-by: Andy Gross <agross@kernel.org>
> >
> > Greg, can you pick this one up?
> >
> > Thanks,
> > Andy
>
> Greg, will this be queued for 5.5?
Yes, catching up now...
next prev parent reply other threads:[~2019-11-04 16:41 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-21 15:46 [PATCH v2] tty: serial: msm_serial: Fix flow control Jeffrey Hugo
2019-10-21 16:26 ` Bjorn Andersson
2019-10-27 5:55 ` Andy Gross
2019-11-03 21:51 ` Jeffrey Hugo
2019-11-04 16:41 ` Greg Kroah-Hartman [this message]
2019-11-04 21:13 ` Jeffrey Hugo
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20191104164123.GA2256087@kroah.com \
--to=gregkh@linuxfoundation.org \
--cc=agross@kernel.org \
--cc=bjorn.andersson@linaro.org \
--cc=jeffrey.l.hugo@gmail.com \
--cc=jslaby@suse.com \
--cc=linux-arm-msm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-serial@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).