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

Peter Griffin
2017-01-30T16:10:41Z

Hi Lee,

On Mon, 30 Jan 2017, Lee Jones wrote:

> On Mon, 30 Jan 2017, Peter Griffin wrote:
>
> > 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-QSEj5FYQhm4dnm+yROfE0A@public.gmane.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.
>
> What makes you think this will break ABI?
>

I've not tried it, but an older DT defines one group, 'default' which contains
the same pin config as your new optional 'manual-rts' group.

The driver now reads like the manual-rts pin config is optional and should be stored in
ascport->states[MANUAL_RTS]. An older DT will pass that same pin config as the default
group and it will be stored in ascport->states[DEFAULT].

That seems wrong to me, and if it executes OK it wouldn't be what you
expect by reading the code.

regards,

Peter.
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