linux-kernel - Re: [PATCH] serial: 8250: 8250_core: Fix irq name for 8250 serial irq

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Message-ID: <20170320123204.GI21222@n2100.armlinux.org.uk>
Date:   Mon, 20 Mar 2017 12:32:04 +0000
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Robin Murphy <robin.murphy@....com>,
        Jisheng Zhang <jszhang@...vell.com>,
        Vignesh R <vigneshr@...com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        Jiri Slaby <jslaby@...e.com>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] serial: 8250: 8250_core: Fix irq name for 8250 serial irq

On Thu, Mar 16, 2017 at 10:58:54PM +0200, Andy Shevchenko wrote:
> On Thu, Mar 16, 2017 at 4:55 PM, Robin Murphy <robin.murphy@....com> wrote:
> > On 16/03/17 13:36, Russell King - ARM Linux wrote:
> >> On Thu, Mar 16, 2017 at 05:56:53PM +0530, Vignesh R wrote:
> >>> Using dev_name() as irq name during request_irq() might be misleading in
> >>> case of serial over PCI. Therefore use a better alternative name for
> >>> identifying serial port irqs as "serial" appended with serial_index of
> >>> the port. This ensures that "serial" string is always present in irq
> >>> name while port index will help in distinguishing b/w different ports.
> >>
> >> Wouldn't it be better to use the device name (iow, ttySx) rather than
> >> "serialx" ?
> >>
> >> Maybe a helper function in serial_core.c to format the device name into
> >> a supplied string, which can be re-used elsewhere, eg, uart_report_port()
> >> and uart_suspend_port().  IOW:
> >>
> >> const char *uart_port_name(char *buf, size_t n, struct uart_driver *drv,
> >>                          struct uart_port *port)
> >> {
> >>       snprintf(buf, n, "%s%d", drv->dev_name,
> >>                drv->tty_driver->name_base + port->line);
> >>
> >>       return buf;
> >> }
> >>
> >> which means you can do this:
> >>
> >>       char name[16];
> >>
> >>       request_irq(..., uart_port_name(name, sizeof(name), driver, port), ...)
> >>
> >> which also avoids the allocation.
> >
> > ...and makes 'cat /proc/interrupts' particularly fun later:
> >
> >   8:          0          GICv2  72 Level     � �h       ����V!
> >
> > Unless a suitably long-lived string already exists somewhere else in the
> > serial core, the allocation is unavoidable, although kasprintf() (or its
> > devm_ variant) might make matters a little simpler.
> 
> What prevents us to create a field in uart_port (uart8250_port?) where
> we put the uart_port_name() for future use as long as uart_port is
> alive?

Probably a good idea - I didn't check whether request_irq() just uses
the pointer to the string or takes a copy of the string (I should've
done before making the suggestion...)

-- 
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