linux-kernel - Re: [PATCH 0/2] Add software flow control support for STM32 UART

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Message-ID: <20200416173710.GA4548@Mani-XPS-13-9360>
Date:   Thu, 16 Apr 2020 23:07:10 +0530
From:   Manivannan Sadhasivam <mani@...nel.org>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre TORGUE <alexandre.torgue@...com>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/2] Add software flow control support for STM32 UART

Hi Andy,

On Mon, Apr 13, 2020 at 12:17:21PM +0300, Andy Shevchenko wrote:
> On Mon, Apr 13, 2020 at 7:06 AM <mani@...nel.org> wrote:
> >
> > From: Manivannan Sadhasivam <mani@...nel.org>
> >
> > Hello,
> >
> > This patchset adds software flow control support for STM32 UART controller.
> > This is necessary for the upcoming STM32MP1 based board called Stinger96
> > IoT-Box. On that board, a bluetooth chip is connected to one of the UART
> > controller but the CTS/RTS lines got swapped mistakenly. So in order to
> > workaround that hardware bug and also to support the usecase of using only
> > Tx/Rx pins, this patchset adds software flow control support.
> >
> > This patchset has been validated w/ Stinger96 IoT-Box connected to Murata
> > WiFi-BT combo chip.
> >
> 
> I think it's a mix of terminology or so. Looking into the patches I
> found that it's required to have GPIOs for SW flow control.
> No, SW flow control does not require any additional signals, except RxD/TxD.
> 

Yikes. Yes I got it wrong. 'st,hw-flow-ctrl' property confused me :)

> On top of that, it seems you adding mctrl-gpio functionality. Why
> can't you use that one? And thus no bindings needs to be updated.
> 

Sure. This looks feasible. Will submit a follow up patch.

Thanks,
Mani

> > Thanks,
> > Mani
> >
> > Manivannan Sadhasivam (2):
> >   dt-bindings: serial: Add binding for software flow control in STM32
> >     UART
> >   tty: serial: Add software flow control support for STM32 USART
> >
> >  .../bindings/serial/st,stm32-uart.yaml        |  15 +-
> >  drivers/tty/serial/stm32-usart.c              | 143 +++++++++++++++++-
> >  drivers/tty/serial/stm32-usart.h              |   4 +
> >  3 files changed, 155 insertions(+), 7 deletions(-)
> >
> > --
> > 2.17.1
> >
> 
> 
> -- 
> With Best Regards,
> Andy Shevchenko