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

From: Lech Perczak
Date: Fri May 19 2023 - 12:01:17 EST


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.
Strzegomska 54,
53-611 Wroclaw
Tel: (+48) 71 75 000 16
Email: lech.perczak@xxxxxxxxxxxxxxx
Website: http://www.camlingroup.com