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

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Date:   Thu, 17 Jan 2019 17:09:44 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     Balakrishna Godavarthi <bgodavar@...eaurora.org>,
        Johan Hovold <johan@...nel.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 Tue, Jan 15, 2019 at 03:46:28PM -0800, Matthias Kaehlcke wrote:

> Using RTS seems|ed like a nice solutions, since it's the native way to
> prevent the controller from sending data, instead of doing some custom
> hack. However Johan seems to be fairly convinced that flow control and
> manual toggling of RTS can be problematic, and we have seen that
> disabling flow control has its own problems. Maybe it's time to
> consider other solutions like the DISCARD_RX flag we discussed
> earlier. Not that I really liked this custom solution, but in the end
> it might be a more robust way to address the issue.
> 
> Johan/Marcel/others: Do you have any further ideas or input on this?

I don't see why deasserting RTS wouldn't work, well at least as long as
the RTS signal is wired correctly.

My point was simply that calling serdev_device_set_rts() will generally
not work unless you first disable automatic (i.e. hw-managed) flow
control using serdev_device_set_flow_control(). The exact behaviour is
serial-controller dependent, but I assume the driver needs to be
platform agnostic.

Johan