linux-kernel - Re: [RFC PATCH 05/22] thunderbolt: Add helper macros to iterate over switch ports

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Message-ID: <20191006121536.6u7noudvfiri5h3s@wunner.de>
Date:   Sun, 6 Oct 2019 14:15:36 +0200
From:   Lukas Wunner <lukas@...ner.de>
To:     Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:     Oliver Neukum <oneukum@...e.com>, linux-usb@...r.kernel.org,
        Anthony Wong <anthony.wong@...onical.com>,
        Mario.Limonciello@...l.com,
        Andreas Noever <andreas.noever@...il.com>,
        Yehezkel Bernat <YehezkelShB@...il.com>,
        Michael Jamet <michael.jamet@...el.com>,
        Rajmohan Mani <rajmohan.mani@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Nicholas Johnson <nicholas.johnson-opensource@...look.com.au>,
        Alan Stern <stern@...land.harvard.edu>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 05/22] thunderbolt: Add helper macros to iterate over
 switch ports

On Wed, Oct 02, 2019 at 05:28:59PM +0300, Mika Westerberg wrote:
> On Wed, Oct 02, 2019 at 04:17:54PM +0200, Oliver Neukum wrote:
> > Am Dienstag, den 01.10.2019, 14:38 +0300 schrieb Mika Westerberg:
> > > @@ -1975,10 +1972,8 @@ void tb_switch_suspend(struct tb_switch *sw)
> > >         if (err)
> > >                 return;
> > >  
> > > -       for (i = 1; i <= sw->config.max_port_number; i++) {
> > > -               if (tb_port_has_remote(&sw->ports[i]))
> > > -                       tb_switch_suspend(sw->ports[i].remote->sw);
> > > -       }
> > > +       tb_switch_for_each_remote_port(sw, i)
> > > +               tb_switch_suspend(sw->ports[i].remote->sw);
> > 
> > This macro looks a bit prone to misunderstanding.
> > I guess the function would be better if the test could be seen.
> 
> The macro does not really save too many lines so I think I can just drop
> this patch for now and keep these open-coded.

Introducing a macro is fine.

However instead of using an index "i" as iterator, I'd suggest using a
pointer to struct tb_port.  This reduces the horizontal width of the
code because you can replace the "sw->ports[i]" with just "port".

In most of the loops this also saves 1 line for an assignment:
"struct tb_port *port = &sw->ports[i];"

In fact, I've already proposed such a macro more than a year ago
but it never got merged:

https://lore.kernel.org/patchwork/patch/983863/ 

/**
 * tb_sw_for_each_port() - iterate over ports on a switch
 * @switch: pointer to struct tb_switch over whose ports shall be iterated
 * @port: pointer to struct tb_port which shall be used as the iterator
 *
 * Excludes port 0, which is the switch itself and therefore irrelevant for
 * most iterations.
 */
#define tb_sw_for_each_port(switch, port)				 \
	for (port = &(switch)->ports[1];				 \
	     port <= &(switch)->ports[(switch)->config.max_port_number]; \
	     port++)

Thanks,

Lukas