From: Johan Hovold <johan@kernel.org>
To: Manivannan Sadhasivam <mani@kernel.org>
Cc: Johan Hovold <johan@kernel.org>,
gregkh@linuxfoundation.org, linux-usb@vger.kernel.org,
linux-kernel@vger.kernel.org, patong.mxl@gmail.com,
Linus Walleij <linus.walleij@linaro.org>,
linux-gpio@vger.kernel.org
Subject: Re: [PATCH v3 2/2] usb: serial: xr_serial: Add gpiochip support
Date: Fri, 29 May 2020 11:00:43 +0200 [thread overview]
Message-ID: <20200529090043.GB19480@localhost> (raw)
In-Reply-To: <20200527030959.GA6129@Mani-XPS-13-9360>
On Wed, May 27, 2020 at 08:39:59AM +0530, Manivannan Sadhasivam wrote:
> Hi,
>
> On Tue, May 19, 2020 at 03:07:40PM +0200, Johan Hovold wrote:
> > On Fri, May 01, 2020 at 12:19:24AM +0530, mani@kernel.org wrote:
> > > From: Manivannan Sadhasivam <mani@kernel.org>
> > >
> > > Add gpiochip support for Maxlinear/Exar USB to serial converter
> > > for controlling the available gpios.
> > > +static int xr21v141x_gpio_init(struct usb_serial_port *port)
> > > +{
> > > + struct xr_port_private *port_priv = usb_get_serial_port_data(port);
> > > + int ret;
> > > + u8 gpio_mode;
> > > +
> > > + port_priv->gc.ngpio = 6;
> > > +
> > > + ret = xr_get_reg(port, XR21V141X_UART_REG_BLOCK,
> > > + port_priv->regs->gpio_mode, &gpio_mode);
> > > + if (ret)
> > > + return ret;
> > > +
> > > + /* Mark all pins which are not in GPIO mode */
> > > + if (gpio_mode & UART_MODE_RTS_CTS)
> > > + port_priv->gpio_altfunc |= (BIT(4) | BIT(5));
> > > + else if (gpio_mode & UART_MODE_DTR_DSR)
> > > + port_priv->gpio_altfunc |= (BIT(2) | BIT(3));
> > > + else if (gpio_mode & UART_MODE_RS485)
> > > + port_priv->gpio_altfunc |= BIT(5);
> > > + else if (gpio_mode & UART_MODE_RS485_ADDR)
> > > + port_priv->gpio_altfunc |= BIT(5);
> > > + else
> > > + port_priv->gpio_altfunc = 0; /* All GPIOs are available */
> >
> > So this clearly isn't sufficient as the serial driver updates the
> > gpio-mode settings at runtime, which means you may have the two drivers
> > interfering with each other.
>
> Agree. I was not sure earlier on how to handle this.
>
> > You probably need to reserve at least CTS/RTS (gpio 4 and 5) for use
> > by the serial driver. But suddenly driving the DSR, RI and CD inputs
> > probably isn't a good idea either.
> >
> > How would you even what know what these pins are used for generally?
> >
> > Perhaps refusing all gpio requests while the port is open and making
> > sure that the serial driver never touches a requested pin could work
> > (including indirectly through hardware flow control, etc).
>
> Is there an API or recommended way to check if the port is open? I
> just see a helper for tty...
You're gonna need to add your own flag and locking as you're
coordinating two distinct drivers.
Johan
next prev parent reply other threads:[~2020-05-29 9:00 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-30 18:49 [PATCH v3 0/2] Add support for MaxLinear/Exar USB to serial converters mani
2020-04-30 18:49 ` [PATCH v3 1/2] usb: serial: Add MaxLinear/Exar USB to Serial driver mani
2020-05-18 6:07 ` Greg KH
2020-05-19 12:33 ` Johan Hovold
2020-06-06 18:45 ` Manivannan Sadhasivam
2020-04-30 18:49 ` [PATCH v3 2/2] usb: serial: xr_serial: Add gpiochip support mani
2020-05-19 13:07 ` Johan Hovold
2020-05-27 3:09 ` Manivannan Sadhasivam
2020-05-29 9:00 ` Johan Hovold [this message]
2020-05-16 7:06 ` [PATCH v3 0/2] Add support for MaxLinear/Exar USB to serial converters Manivannan Sadhasivam
2020-06-05 11:13 ` Mauro Carvalho Chehab
2020-06-06 12:27 ` Manivannan Sadhasivam
2020-06-05 12:40 ` Mauro Carvalho Chehab
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200529090043.GB19480@localhost \
--to=johan@kernel.org \
--cc=gregkh@linuxfoundation.org \
--cc=linus.walleij@linaro.org \
--cc=linux-gpio@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-usb@vger.kernel.org \
--cc=mani@kernel.org \
--cc=patong.mxl@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).