Re: [RFC PATCH v2 2/2] serial: sc16is7xx: fix regression with GPIO configuration

[Lech Perczak <lech.perczak@xxxxxxxxxxxxxxx>]

W dniu 19.05.2023 o 15:30, Hugo Villeneuve pisze:
> On Fri, 19 May 2023 15:00:58 +0200
> Lech Perczak <lech.perczak@xxxxxxxxxxxxxxx> wrote:
>
>> Hello Hugo,
>>
>> A couple of remarks inline.
>>
>> W dniu 18.05.2023 o 15:29, Hugo Villeneuve pisze:
>>> From: Hugo Villeneuve <hvilleneuve@xxxxxxxxxxxx>
>>>
>>> Commit 679875d1d880 ("sc16is7xx: Separate GPIOs from modem control lines")
>>> and commit 21144bab4f11 ("sc16is7xx: Handle modem status lines")
>>> changed the function of the GPIOs pins to act as modem control
>>> lines without any possibility of selecting GPIO function.
>>>
>>> As a consequence, applications that depends on GPIO lines configured
>>> by default as GPIO pins no longer work as expected.
>>>
>>> Also, the change to select modem control lines function was done only
>>> for channel A of dual UART variants (752/762). This was not documented
>>> in the log message.
>>>
>>> This new patch allows to specify GPIO or modem control line function
>>> in the device tree, and for each of the ports (A or B).
>>>
>>> This is done by using the new device-tree property named
>>> "modem-control-line-ports" (property added in separate patch).
>>>
>>> Boards that need to have GPIOS configured as modem control lines
>>> should add that property to their device tree. Here is a list of
>>> boards using the sc16is7xx driver in their device tree and that may
>>> need to be modified:
>>>     arm64/boot/dts/freescale/fsl-ls1012a-frdm.dts
>>>     mips/boot/dts/ingenic/cu1830-neo.dts
>>>     mips/boot/dts/ingenic/cu1000-neo.dts
>>>
>>> Fixes: 679875d1d880 ("sc16is7xx: Separate GPIOs from modem control lines")
>>> Fixes: 21144bab4f11 ("sc16is7xx: Handle modem status lines")
>>> Signed-off-by: Hugo Villeneuve <hvilleneuve@xxxxxxxxxxxx>
>>> ---
>>> v1 -> v2: Rebase because original patch did not apply properly
>>>           Add git base-commit
>>>
>>>  drivers/tty/serial/sc16is7xx.c | 42 ++++++++++++++++++++--------------
>>>  1 file changed, 25 insertions(+), 17 deletions(-)
>>>
>>> diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
>>> index abad091baeea..4e3d2325ef6e 100644
>>> --- a/drivers/tty/serial/sc16is7xx.c
>>> +++ b/drivers/tty/serial/sc16is7xx.c
>>> @@ -236,7 +236,8 @@
>>>
>>>  /* IOControl register bits (Only 750/760) */
>>>  #define SC16IS7XX_IOCONTROL_LATCH_BIT  (1 << 0) /* Enable input latching */
>>> -#define SC16IS7XX_IOCONTROL_MODEM_BIT  (1 << 1) /* Enable GPIO[7:4] as modem pins */
>>> +#define SC16IS7XX_IOCONTROL_MODEM_A_BIT        (1 << 1) /* Enable GPIO[7:4] as modem A pins */
>>> +#define SC16IS7XX_IOCONTROL_MODEM_B_BIT        (1 << 2) /* Enable GPIO[3:0] as modem B pins */
>>>  #define SC16IS7XX_IOCONTROL_SRESET_BIT (1 << 3) /* Software Reset */
>>>
>>>  /* EFCR register bits */
>>> @@ -306,7 +307,6 @@ struct sc16is7xx_devtype {
>>>         char    name[10];
>>>         int     nr_gpio;
>>>         int     nr_uart;
>>> -       int     has_mctrl;
>>>  };
>>>
>>>  #define SC16IS7XX_RECONF_MD            (1 << 0)
>>> @@ -447,35 +447,30 @@ static const struct sc16is7xx_devtype sc16is74x_devtype = {
>>>         .name           = "SC16IS74X",
>>>         .nr_gpio        = 0,
>>>         .nr_uart        = 1,
>>> -       .has_mctrl      = 0,
>>>  };
>>>
>>>  static const struct sc16is7xx_devtype sc16is750_devtype = {
>>>         .name           = "SC16IS750",
>>> -       .nr_gpio        = 4,
>>> +       .nr_gpio        = 8,
>>>         .nr_uart        = 1,
>>> -       .has_mctrl      = 1,
>>>  };
>>>
>>>  static const struct sc16is7xx_devtype sc16is752_devtype = {
>>>         .name           = "SC16IS752",
>>> -       .nr_gpio        = 0,
>>> +       .nr_gpio        = 8,
>>>         .nr_uart        = 2,
>>> -       .has_mctrl      = 1,
>>>  };
>>>
>>>  static const struct sc16is7xx_devtype sc16is760_devtype = {
>>>         .name           = "SC16IS760",
>>> -       .nr_gpio        = 4,
>>> +       .nr_gpio        = 8,
>>>         .nr_uart        = 1,
>>> -       .has_mctrl      = 1,
>>>  };
>>>
>>>  static const struct sc16is7xx_devtype sc16is762_devtype = {
>>>         .name           = "SC16IS762",
>>> -       .nr_gpio        = 0,
>>> +       .nr_gpio        = 8,
>>>         .nr_uart        = 2,
>>> -       .has_mctrl      = 1,
>>>  };
>>>
>>>  static bool sc16is7xx_regmap_volatile(struct device *dev, unsigned int reg)
>>> @@ -1456,12 +1451,6 @@ static int sc16is7xx_probe(struct device *dev,
>>>                                      SC16IS7XX_EFCR_RXDISABLE_BIT |
>>>                                      SC16IS7XX_EFCR_TXDISABLE_BIT);
>>>
>>> -               /* Use GPIO lines as modem status registers */
>>> -               if (devtype->has_mctrl)
>>> -                       sc16is7xx_port_write(&s->p[i].port,
>>> -                                            SC16IS7XX_IOCONTROL_REG,
>>> -                                            SC16IS7XX_IOCONTROL_MODEM_BIT);
>>> -
>>>                 /* Initialize kthread work structs */
>>>                 kthread_init_work(&s->p[i].tx_work, sc16is7xx_tx_proc);
>>>                 kthread_init_work(&s->p[i].reg_work, sc16is7xx_reg_proc);
>>> @@ -1497,6 +1486,25 @@ static int sc16is7xx_probe(struct device *dev,
>>>                                          prop, p, u)
>>>                         if (u < devtype->nr_uart)
>>>                                 s->p[u].irda_mode = true;
>>> +
>>> +               val = 0;
>>> +
>>> +               of_property_for_each_u32(dev->of_node, "nxp,modem-control-line-ports",
>>> +                                        prop, p, u)
>> The general idea looks solid to me.
>> I think, that with this property set, we should also reduce number of GPIOs exported by gpiochip.
> OK, I will look into that.
>
>>> +                       if (u < devtype->nr_uart) {
>>> +                               /* Use GPIO lines as modem control lines */
>>> +                               if (u == 0)
>>> +                                       val |= SC16IS7XX_IOCONTROL_MODEM_A_BIT;
>>> +                               else if (u == 1)
>>> +                                       val |= SC16IS7XX_IOCONTROL_MODEM_B_BIT;
>>> +                       }
>>> +
>>> +               if (val)
>>> +                       regmap_update_bits(
>>> +                               s->regmap,
>>> +                               SC16IS7XX_IOCONTROL_REG << SC16IS7XX_REG_SHIFT,
>>> +                               SC16IS7XX_IOCONTROL_MODEM_A_BIT |
>>> +                               SC16IS7XX_IOCONTROL_MODEM_B_BIT, val);
>> I just had a chance to test this on my hardware (with SC16IS760), and something still doesn't work.
>> When looking into /sys/kernel/debug/regmap/<device>/registers,
>> it seems like the proper bits are set, also taking the regmap shift into account.
>> For reference - I did my test basing on v6.4-rc2.
>>
>> I used a loopback plug and statserial to perform the test.
>> Without your patch, when DTR is set, all other pins (DCD, DSR, RI) are set. With it - they are cleared, according to statserial.
> It is strange, because the only conceptual change is the moment in time when we set the IOControl register. Before, IOControl was set within the for/loop for initializing each port. Now it is done after.
>
> Maybe you could try to put the section that reads the DT property just after resetting the device.
>
> While suggesting this, I just noticed that when the device is reset, we do not wait before initiating communication with the device. Thefore, I would suggest the following change (that I will submit as a separate patch):
>
>         regmap_write(s->regmap, SC16IS7XX_IOCONTROL_REG << SC16IS7XX_REG_SHIFT,
>                         SC16IS7XX_IOCONTROL_SRESET_BIT);
>
> +       /* After reset, the host must wait at least 3us before initializing a
> +        * communication with the device: */
> +       usleep_range(3, 5);
>
> Then like I said, insert the code that read the modem-control-line-port DT property right after that to see if it helps.
>
> Hugo.

Hello,

I tried those suggestions, together with the patch you mentioned in the other email - all to no avail.
I added a debug print to confirm, that the property is detected, and regmap access is executed - and it is. This is so strange.
Maybe the offsets in regmap are still wrong, for some reason?
I also double checked if it was possible to alter and check GPIO states through GPIO subsystem - it is.

-- 
Pozdrawiam/With kind regards,
Lech Perczak

Sr. Software Engineer
Camlin Technologies Poland Limited Sp. z o.o.
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Email:   lech.perczak@xxxxxxxxxxxxxxx
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