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

From: Lech Perczak
Date: Fri May 19 2023 - 09:01:27 EST

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.
> + 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.
> }
>
> #ifdef CONFIG_GPIOLIB
> --
> 2.30.2
>
>
--
Pozdrawiam/With kind regards,
Lech Perczak

Sr. Software Engineer
Camlin Technologies Poland Limited Sp. z o.o.
Strzegomska 54,
53-611 Wroclaw
Tel: (+48) 71 75 000 16
Email: lech.perczak@xxxxxxxxxxxxxxx
Website: http://www.camlingroup.com