linux-kernel - Re: [PATCH 2/5] input: Use driver hint to compute the evdev buffer size (rev3)

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Message-ID: <20100623171206.GA11512@core.coreip.homeip.net>
Date:	Wed, 23 Jun 2010 10:12:06 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Henrik Rydberg <rydberg@...omail.se>
Cc:	Ping Cheng <pinglinux@...il.com>, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org, Jiri Kosina <jkosina@...e.cz>,
	Ping Cheng <pingc@...om.com>,
	Benjamin Tissoires <tissoire@...a.fr>,
	Chase Douglas <chase.douglas@...onical.com>,
	Rafi Rubin <rafi@...s.upenn.edu>
Subject: Re: [PATCH 2/5] input: Use driver hint to compute the evdev buffer
 size (rev3)

On Wed, Jun 23, 2010 at 07:07:44PM +0200, Henrik Rydberg wrote:
> Hi Ping,
> [...]
> >> @@ -51,7 +52,9 @@ static DEFINE_MUTEX(evdev_table_mutex);
> >>
> >>  static int evdev_compute_buffer_size(struct input_dev *dev)
> >>  {
> >> -       return EVDEV_MIN_BUFFER_SIZE;
> >> +       int nev = dev->hint_events_per_packet * EVDEV_BUF_PACKETS;
> >> +       nev = max(nev, EVDEV_MIN_BUFFER_SIZE);
> >> +       return roundup_pow_of_two(nev);
> > 
> > I think we have a backward compatibility issue here. This routine will
> > return 7 when nev falls to the default value
> > (EVDEV_MIN_BUFFER_SIZE/64).  This could happen to those drivers that
> > don't report MT events or forget/don't feel the need to set
> > hint_events_per_packet since the old BUFFER_SIZE worked perfectly for
> > them.  We need to keep the return value for those drivers as 64 so we
> > could allocate the same space as it was in [PATCH 1/5].
> 
> Are you perhaps confusing EVDEV_BUF_PACKETS and EVDEV_MIN_BUFFER_SIZE? The last
> line ensures that the value returned is a power of two (hence not 7). The
> second-to-last line ensures the value is at least equal to 64 (hence not 7). The
> default hint value for a driver that does not do anything is zero, which leads
> to a return value of 64, just as it is today.
> 

I think Ping might have confused roundup_pow_of_two() with
get_order()-type function...

Anyways, applied all 5, thanks Henrik.

-- 
Dmitry
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