Messages in this thread | | | Date | Wed, 23 Jun 2010 19:07:44 +0200 | From | Henrik Rydberg <> | Subject | Re: [PATCH 2/5] input: Use driver hint to compute the evdev buffer size (rev3) |
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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.
Thanks, Henrik
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