linux-kernel - Re: [STLinux Kernel] [PATCH 3/8] serial: st-asc: Read in all Pinctrl states

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Message-ID: <20170130142356.GA18710@griffinp-ThinkPad-X1-Carbon-2nd>
Date:   Mon, 30 Jan 2017 14:23:56 +0000
From:   Peter Griffin <peter.griffin@...aro.org>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     gregkh@...uxfoundation.org, jslaby@...e.com,
        linux-serial@...r.kernel.org, robh+dt@...nel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kernel@...inux.com
Subject: Re: [STLinux Kernel] [PATCH 3/8] serial: st-asc: Read in all Pinctrl
 states

Hi Lee,

On Fri, 27 Jan 2017, Lee Jones wrote:

> On Wed, 25 Jan 2017, Peter Griffin wrote:
> 
> > Hi Lee,
> > 
> > On Tue, 24 Jan 2017, Lee Jones wrote:
> > 
> > > There are now 2 possible separate/different Pinctrl states which can
> > > be provided from platform data.  One which encompasses the lines
> > > required for HW flow-control (CTS/RTS) and another which does not
> > > specify these lines, such that they can be used via GPIO mechanisms
> > > for manually toggling (i.e. from a request by `stty`).
> > > 
> > > Signed-off-by: Lee Jones <lee.jones@...aro.org>
> > > ---
> > >  drivers/tty/serial/st-asc.c | 28 ++++++++++++++++++++++++++++
> > >  1 file changed, 28 insertions(+)
> > > 
> > > diff --git a/drivers/tty/serial/st-asc.c b/drivers/tty/serial/st-asc.c
> > > index 397df50..03801ed 100644
> > > --- a/drivers/tty/serial/st-asc.c
> > > +++ b/drivers/tty/serial/st-asc.c
> > > @@ -37,10 +37,16 @@
> > >  #define ASC_FIFO_SIZE 16
> > >  #define ASC_MAX_PORTS 8
> > >  
> > > +/* Pinctrl states */
> > > +#define DEFAULT		0
> > > +#define MANUAL_RTS	1
> > 
> > Nit: Would be better to have them aligned.
> 
> These are aligned in code.  The patch format throws things out.
> 
> Look, same lines with the "> > +" removed:

Ah OK.

> 
> /* Pinctrl states */
> #define DEFAULT		0
> #define MANUAL_RTS	1
> 
> Try it.
> 
> > > +
> > >  struct asc_port {
> > >  	struct uart_port port;
> > >  	struct gpio_desc *rts;
> > >  	struct clk *clk;
> > > +	struct pinctrl *pinctrl;
> > > +	struct pinctrl_state *states[2];
> > >  	unsigned int hw_flow_control:1;
> > >  	unsigned int force_m1:1;
> > >  };
> > > @@ -694,6 +700,7 @@ static int asc_init_port(struct asc_port *ascport,
> > >  {
> > >  	struct uart_port *port = &ascport->port;
> > >  	struct resource *res;
> > > +	int ret;
> > >  
> > >  	port->iotype	= UPIO_MEM;
> > >  	port->flags	= UPF_BOOT_AUTOCONF;
> > > @@ -720,6 +727,27 @@ static int asc_init_port(struct asc_port *ascport,
> > >  	WARN_ON(ascport->port.uartclk == 0);
> > >  	clk_disable_unprepare(ascport->clk);
> > >  
> > > +	ascport->pinctrl = devm_pinctrl_get(&pdev->dev);
> > > +	if (IS_ERR(ascport->pinctrl)) {
> > > +		ret = PTR_ERR(ascport->pinctrl);
> > > +		dev_err(&pdev->dev, "Failed to get Pinctrl: %d\n", ret);
> > > +	}
> > > +
> > > +	ascport->states[DEFAULT] =
> > > +		pinctrl_lookup_state(ascport->pinctrl, "default");
> > > +	if (IS_ERR(ascport->states[DEFAULT])) {
> > > +		ret = PTR_ERR(ascport->states[DEFAULT]);
> > > +		dev_err(&pdev->dev,
> > > +			"Failed to look up Pinctrl state 'default': %d\n", ret);
> > > +		return ret;
> > > +	}
> > > +
> > > +	/* "manual-rts" state is optional */
> > > +	ascport->states[MANUAL_RTS] =
> > > +		pinctrl_lookup_state(ascport->pinctrl, "manual-rts");
> > > +	if (IS_ERR(ascport->states[MANUAL_RTS]))
> > > +		ascport->states[MANUAL_RTS] = NULL;
> > > +
> > 
> > The different pinctrl states looks like a neat solution to the problem.
> > 
> > My only concern here is that 'default' state is implying a hw-flow-control
> > pinmux config, and manual-rts is implying what is the current upstream
> > 'default' pinmux config.
> > 
> > Which maybe ok if you update all uarts, but currently only serial0
> > is updated. So the other uarts current 'default' is actually the same as serial0
> > 'manual-rts' grouping, which conceptually is odd.
> > 
> > Would it not be better to make 'manual-rts' the default state? As that aligns
> > to what is currently already the default for the other UARTS? And then make
> > hw-flow-control the optional state for serial0?
> > 
> > That also has the advantage that 'default' has the same meaning with older DT's.
> 
> The reason it was done is this was because none of the other UARTs
> require 2 separate Pinctrl configurations, only this one.  Moreover,
> if they support RTS/CTS then I believe that the lines should be
> defined in Pinctrl.

Yes I agree with that.

> Thus, it was my plan to update all UART's default
> Pinctrl configs to include the RTS/CTS lines.
> 

I still don't see the point in changing the meaning of 'default' group and breaking
ABI if you don't need to?

As far as I can tell if you swap the meaning of 'default' and 'maunal-rts'
groups you get all the benefits of this series whilst also maintaining backwards
compatbility with older DT's.

regards,

Peter.