linux-kernel - Re: [PATCH v5 2/5] Bluetooth: hci_qca: Deassert RTS while baudrate change command

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Message-ID: <20190122213936.GH261387@google.com>
Date:   Tue, 22 Jan 2019 13:39:36 -0800
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Johan Hovold <johan@...nel.org>
Cc:     Balakrishna Godavarthi <bgodavar@...eaurora.org>,
        marcel@...tmann.org, johan.hedberg@...il.com,
        linux-kernel@...r.kernel.org, linux-bluetooth@...r.kernel.org,
        hemantg@...eaurora.org, linux-arm-msm@...r.kernel.org,
        Johan Hovold <jhovold@...il.com>
Subject: Re: [PATCH v5 2/5] Bluetooth: hci_qca: Deassert RTS while baudrate
 change command

On Mon, Jan 21, 2019 at 09:56:13AM +0100, Johan Hovold wrote:
> On Fri, Jan 18, 2019 at 04:31:09PM -0800, Matthias Kaehlcke wrote:
> > On Fri, Jan 18, 2019 at 10:44:16AM +0100, Johan Hovold wrote:
> > > On Thu, Jan 17, 2019 at 09:21:09AM -0800, Matthias Kaehlcke wrote:
> > > 
> > > > I observed that the qcom_geni_serial driver doesn't raise RTS with
> > > > flow control disabled. It seems we have to investigate why that's the
> > > > case. I agree that the driver should be platform agnostic.
> > > 
> > > Sounds like a driver bug, unless the hardware is just "odd". The
> > > driver implementation of this looks very non-standard judging from a
> > > quick peek.
> > > 
> > > In fact, qcom_geni_serial_get_mctrl() is currently a no-op if hardware
> > > flow control is not enabled:
> > > 
> > > 	if (uart_console(uport) || !uart_cts_enabled(uport))
> > > 		return;
> > > 
> > > Perhaps dropping the !uart_cts_enabled() test is sufficient.
> > 
> > Thanks for taking a look Johan, that was indeed the problem (also
> > in set_mctrl()). I posted a fix: https://lore.kernel.org/patchwork/patch/1033611/
> 
> Nice (I did mean set_mctrl() above, as I think you noticed).
> 
> > Balakrishna, the following (applied on top of your patch) works for me
> > with the UART patch above:
> > 
> > diff --git a/drivers/bluetooth/hci_qca.c b/drivers/bluetooth/hci_qca.c
> > index 9d5e41f159c78f..60bfdf01f72841 100644
> > --- a/drivers/bluetooth/hci_qca.c
> > +++ b/drivers/bluetooth/hci_qca.c
> > @@ -1080,7 +1080,7 @@ static int qca_set_speed(struct hci_uart *hu, enum qca_speed_type speed_type)
> >  {
> >  	unsigned int speed, qca_baudrate;
> >  	struct qca_serdev *qcadev;
> > -	int ret;
> > +	int ret = 0;
> >  
> >  	if (speed_type == QCA_INIT_SPEED) {
> >  		speed = qca_get_speed(hu, QCA_INIT_SPEED);
> > @@ -1097,22 +1097,27 @@ static int qca_set_speed(struct hci_uart *hu, enum qca_speed_type speed_type)
> >  		 * the old speed.
> >  		 */
> >  		qcadev = serdev_device_get_drvdata(hu->serdev);
> > -		if (qcadev->btsoc_type == QCA_WCN3990)
> > +		if (qcadev->btsoc_type == QCA_WCN3990) {
> > +			hci_uart_set_flow_control(hu, true);
> 
> Wow, yeah, this parameter inversion is indeed confusing...
> 
> >  			serdev_device_set_rts(hu->serdev, false);
> > +		}
> 
> But looking at hci_uart_set_flow_control() now, it actually also
> deasserts RTS. So all you need here is the hci_uart_set_flow_control()
> call.  

Great, thanks for pointing that out!

> And that makes the inversion make a bit more sense too, even if the
> naming is a bit unfortunate with respect to
> serdev_device_set_flow_control() at least.