RE: [PATCH 2/2] pinctrl: pinctrl-imx: do not assume mux 0 is gpio

["A.S. Dong" <aisheng.dong@xxxxxxx>]

Hi Stefan,

> -----Original Message-----
> From: A.S. Dong
> Sent: Thursday, May 18, 2017 3:00 PM
> To: 'Stefan Agner'
> Cc: linux-gpio@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx;
> linus.walleij@xxxxxxxxxx; shawnguo@xxxxxxxxxx; Jacky Bai; Andy Duan;
> kernel@xxxxxxxxxxxxxx; Alexandre Courbot
> Subject: RE: [PATCH 2/2] pinctrl: pinctrl-imx: do not assume mux 0 is gpio
> 
> > -----Original Message-----
> > From: Stefan Agner [mailto:stefan@xxxxxxxx]
> > Sent: Thursday, May 18, 2017 2:16 AM
> > To: A.S. Dong
> > Cc: linux-gpio@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx;
> > linus.walleij@xxxxxxxxxx; shawnguo@xxxxxxxxxx; Jacky Bai; Andy Duan;
> > kernel@xxxxxxxxxxxxxx; Alexandre Courbot
> > Subject: Re: [PATCH 2/2] pinctrl: pinctrl-imx: do not assume mux 0 is
> > gpio
> >
> > On 2017-05-17 00:18, A.S. Dong wrote:
> > >> -----Original Message-----
> > >> From: Stefan Agner [mailto:stefan@xxxxxxxx]
> > >> Sent: Tuesday, May 16, 2017 1:27 AM
> > >> To: A.S. Dong
> > >> Cc: linux-gpio@xxxxxxxxxxxxxxx;
> > >> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx;
> > >> linus.walleij@xxxxxxxxxx; shawnguo@xxxxxxxxxx; Jacky Bai; Andy
> > >> Duan; kernel@xxxxxxxxxxxxxx; Alexandre Courbot
> > >> Subject: Re: [PATCH 2/2] pinctrl: pinctrl-imx: do not assume mux 0
> > >> is gpio
> > >>
> > >> On 2017-05-14 23:48, Dong Aisheng wrote:
> > >> > Do not assume MUX 0 is GPIO function in core driver as a
> > >> > different SoC may have different value. e.g. MX7ULP Mux 1 is GPIO.
> > >> >
> > >> > Cc: Linus Walleij <linus.walleij@xxxxxxxxxx>
> > >> > Cc: Alexandre Courbot <gnurou@xxxxxxxxx>
> > >> > Cc: Shawn Guo <shawnguo@xxxxxxxxxx>
> > >> > Cc: Stefan Agner <stefan@xxxxxxxx>
> > >> > Cc: Fugang Duan <fugang.duan@xxxxxxx>
> > >> > Cc: Bai Ping <ping.bai@xxxxxxx>
> > >> > Signed-off-by: Dong Aisheng <aisheng.dong@xxxxxxx>
> > >> > ---
> > >> >  drivers/pinctrl/freescale/pinctrl-imx.c | 3 ++-
> > >> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > >> >
> > >> > diff --git a/drivers/pinctrl/freescale/pinctrl-imx.c
> > >> > b/drivers/pinctrl/freescale/pinctrl-imx.c
> > >> > index 0d6aaca..ed8ea32 100644
> > >> > --- a/drivers/pinctrl/freescale/pinctrl-imx.c
> > >> > +++ b/drivers/pinctrl/freescale/pinctrl-imx.c
> > >> > @@ -281,7 +281,7 @@ static int imx_pmx_gpio_request_enable(struct
> > >> > pinctrl_dev *pctldev,
> > >> >  			continue;
> > >> >  		for (pin = 0; pin < grp->num_pins; pin++) {
> > >> >  			imx_pin = &((struct imx_pin *)(grp->data))[pin];
> > >> > -			if (imx_pin->pin == offset && !imx_pin->mux_mode)
> > >> > +			if (imx_pin->pin == offset)
> > >> >  				goto mux_pin;
> > >>
> > >> The reason I added that check was to make sure we pick a mux option
> > >> which is GPIO... With this change, any pinmux might be picked...
> > >>
> > >
> > > First of all, this seems to be wrong to me that GPIO mux mode is SoC
> > > Dependant and should not be put in pinctrl-imx core driver.
> >
> > Hm, agree, we should consider to move
> > imx_pmx_gpio_request_enable/disable_free and
> > imx_pmx_gpio_set_direction into pinctrl-vf610.c
> >
> 
> IMX7ULP may want to use imx_pmx_gpio_set_direction as well to support
> dynamically change GPIO from output to input.
> 
> > >
> > > Secondly, I think we may be over worried and it's not quite
> > > necessary As we did not do the sanity check for both raw config and
> > > mux data read From Device tree, why only do it for GPIO?
> > >
> > > We may trust the data in device tree.
> >
> > In Vybrid, there is no need to explicitly assign a pinmux to use a pin
> > as GPIO. So the pinmux could be anything... The implemented semantics
> > for Vyrbid is really different than i.MX, see below.
> >
> 
> Strange, I do see Vybrid assigning pinmux to GPIO in device tree.
> e.g.
> arch/arm/boot/dts/vf-colibri.dtsi
> pinctrl_esdhc1: esdhc1grp {
>         fsl,pins = <
>                 VF610_PAD_PTA24__ESDHC1_CLK     0x31ef
>                 VF610_PAD_PTA25__ESDHC1_CMD     0x31ef
>                 VF610_PAD_PTA26__ESDHC1_DAT0    0x31ef
>                 VF610_PAD_PTA27__ESDHC1_DAT1    0x31ef
>                 VF610_PAD_PTA28__ESDHC1_DATA2   0x31ef
>                 VF610_PAD_PTA29__ESDHC1_DAT3    0x31ef
>                 VF610_PAD_PTB20__GPIO_42        0x219d
>         >;
> };
> 
> > >
> > >> >  		}
> > >> >  	}
> > >> > @@ -292,6 +292,7 @@ static int imx_pmx_gpio_request_enable(struct
> > >> > pinctrl_dev *pctldev,
> > >> >  	reg = readl(ipctl->base + pin_reg->mux_reg);
> > >> >  	reg &= ~info->mux_mask;
> > >> >  	reg |= imx_pin->config;
> > >> > +	reg |= imx_pin->mux_mode << info->mux_shift;
> > >>
> > >> ... and muxed...
> > >>
> > >> Not sure if we want that.
> > >>
> > >> I had to control GPIO output/input through pinctrl since Vybrid
> > >> does not allow to control that from the GPIO block.
> > >>
> > >> However, according to your GPIO patchset, the i.MX 7ULP has a new
> > >> register GPIO_PDDR to control output from the GPIO block. Is
> > >> controlling the output driver from IOMUXC still required?
> > >
> > > Yes, it's still required.
> > >
> >
> > That sounds weird, what is the GPIO_PDDR for then? Sure I  need to
> > enable the output driver to drive the pin, but can I disable output
> > just using GPIO_PDDR?
> 
> No, to fully disable a output, you must disable OBE as well.
> 
> >
> > Maybe we have a miss understanding here:
> >
> > Lets assume we want to switch a GPIO between output and input:
> >
> > echo "output" > /sys/class/gpio/gpioN/direction ..
> > echo "input" > /sys/class/gpio/gpioN/direction
> >
> > Do I need to disable the output driver in the IOMUXC or can we just
> > disable GPIO_PDDR and use the pin as input?
> >
> 
> OBE should also be disabled. Otherwise the input may not function well.
> 
> > If we can disable the output driver just using GPIO_PDDR, we can avoid
> > the gpio_set_direction cross call.
> >
> >
> > >> If not, I really would just not use all that "find pinctrl config"
> > >> hackery... e.g. add a new flag, USE_IOMUXC_FOR_GPIO_OUTPUT, and set
> > >> that only for Vybrid.
> > >>
> > >> This would also align much better with the other i.MX devices,
> > >> where pinmuxing and GPIO is completely orthogonal.
> > >>
> > >
> > > Actually this patch came only because to make the exist code not
> > > break MX7ULP.
> > >
> > > Actually I'm wondering why we need implement
> > > imx_pmx_gpio_request_enable function?
> > >
> > > Per my understanding, IMX binding already set GPIO mux by Parsing
> > > MUX mode from device tree, so why need gpio_request_enable which
> > > looks like is duplicated.
> > >
> > > Can you help explain it?
> >
> > I suggest to read this clarification email wrt to pinctrl/gpio from
> > Linus
> > Walleij:
> > https://lkml.org/lkml/2016/10/10/87
> >
> > To summarize: We have different semantics in Vybrid: The GPIO
> > subsystem automatically mux the GPIO for you. So in Vybrid, you do not
> > have to mux a GPIO (but a valid entry in your device tree is needed,
> > but does not assigned to any node).
> 
> Okay, Clearer now.
> 
> But I do see the users of GPIO pads in Vybrid dts.
> Above is an example which make me confuse at first.
> 
> >
> > Is what the driver is doing for Vybrid wrong? It is different from
> > i.MX, but afaik, it is not really wrong... Its a valid implementation
> > according to the currently defined semantics...  Due to the *need* to
> > touch pinctrl for direction, I had to implement cross calls anyway, so
> > I thought I might as well go full mile and also mux the GPIO on
> request...
> >
> 
> It's not strickly wrong.
> Just a bit confuse that gpio_request_enable seems not quite necessary As
> we actually already and must define GPIO mux in device tree according To
> standard IMX binding format.
> e.g. VF610_PAD_PTB20__GPIO_42 in above sd pad group.
> That means pinctrl already does the GPIO mux when enable sd function.
> 
> > So the question is, what semantic do we want for i.MX 7ULP? Since it
> > is a i.MX device, we probably want the same semantics as i.MX 6/7 is
> > already using for the sake of consistency. So in this case the
> > gpio_request_enable/disable callbacks are not needed...
> >
> > This is how I hope we can do the implementation for i.MX 7ULP:
> > - Do not use gpio_request_enable/disable
> 
> Yes, we do want that.
> 
> > - Do not use gpio_set_direction either
> 
> Not, ULP needs it to support GPIO direction switch.
> 
> > - Users using a GPIO should enable output driver in IOMUXC (just use a
> > pin configuration where output driver is enabled)
> 
> Users still need configure OBE/IBE in devicetree for statically assignment.
> 
> > - The GPIO driver only enables/disables the output driver using its
> > GPIO_PDDR register depending on GPIO direction
> 
> No, same reason as the second question.
> 
> 
> So, finnaly, I think the solution may be:
> 1. If Vybrid does not use gpio_request_enable/disable, we can simply
> remove it. Both driver keeps using pinctrl gpio_set_direction.
> 
> Or.
> 
> 2. Make gpio_request_enable/disable and gpio_set_direction As pinctrl-imx
> core driver callbacks. And only assign gpio_set_direction For IMX7ULP
> platform driver while assign both for Vybrid.
> 
> Which one would you prefer?
> 

Any answer about it?

Regards
Dong Aisheng
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