linux-kernel - Re: [PATCH v4 7/9] serial: sc16is7xx: fix regression with GPIO configuration

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Message-Id: <20230530113649.73f28b9f6ba91f17ace1e12f@hugovil.com>
Date:   Tue, 30 May 2023 11:36:49 -0400
From:   Hugo Villeneuve <hugo@...ovil.com>
To:     andy.shevchenko@...il.com
Cc:     gregkh@...uxfoundation.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
        jirislaby@...nel.org, jringle@...dpoint.com,
        l.perczak@...lintechnologies.com, tomasz.mon@...lingroup.com,
        linux-serial@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org,
        Hugo Villeneuve <hvilleneuve@...onoff.com>
Subject: Re: [PATCH v4 7/9] serial: sc16is7xx: fix regression with GPIO
 configuration

On Tue, 30 May 2023 01:38:17 +0300
andy.shevchenko@...il.com wrote:

> Mon, May 29, 2023 at 10:07:09AM -0400, Hugo Villeneuve kirjoitti:
> > From: Hugo Villeneuve <hvilleneuve@...onoff.com>
> > 
> > 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.
> > 
> > Allow to specify GPIO or modem control line function in the device
> > tree, and for each of the ports (A or B).
> > 
> > Do so by using the new device-tree property named
> > "modem-control-line-ports" (property added in separate patch).
> > 
> > When registering GPIO chip controller, mask-out GPIO pins declared as
> > modem control lines according to this new "modem-control-line-ports"
> > DT property.
> > 
> > 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")
> 
> Don't forget to refer to the dependency patches form this series.
> (I forgot how it should be done, IIRC the documentation about stable kernel
> patches can shed a light on this.)

Hi,
I will look into it.


> ...
> 
> > +	switch (mctrl_mask) {
> > +	case 0:
> > +		s->gpio_valid_mask = 0xFF;
> 
> GENMASK()
> 
> > +		break;
> > +	case SC16IS7XX_IOCONTROL_MODEM_A_BIT:
> > +		s->gpio_valid_mask = 0x0F;
> 
> GENMASK()
> 
> > +		break;
> > +	case SC16IS7XX_IOCONTROL_MODEM_B_BIT:
> > +		s->gpio_valid_mask = 0xF0;
> 
> GENMASK()

Ok done, altough even if in general I like the bit manipulation macros because they make the code easier to read/understand, I find it less obvious by using GENMASK in this case IMMO.


> > +		break;
> > +	default:
> > +		break;
> > +	}
> 
> ...
> 
> > +		of_property_for_each_u32(dev->of_node, "nxp,modem-control-line-ports",
> > +					 prop, p, u) {
> > +			if (u >= devtype->nr_uart)
> > +				continue;
> > +
> > +			/* Use GPIO lines as modem control lines */
> > +			if (u == 0)
> > +				mctrl_mask |= SC16IS7XX_IOCONTROL_MODEM_A_BIT;
> > +			else if (u == 1)
> > +				mctrl_mask |= SC16IS7XX_IOCONTROL_MODEM_B_BIT;
> > +		}
> 
> Can we use device properties, please?

I have converted this section to use device_property_count_u32() and device_property_read_u32_array(). Is that Ok?

> If you think about backporting to the earlier kernels (w/o properties in use in
> this driver), perhaps an additional followup for that?

I am not sure what you mean by this?