linux-kernel - [RFC] Can we bypass the timeout when resetting Synaptics device?

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Message-ID: <CADjb_WTNJJpmpNCOGxdUOd1AZ8S7iEf2NnSHC=VC6TzAOTbP_w@mail.gmail.com>
Date:	Mon, 27 Jun 2016 21:04:58 +0800
From:	Yu Chen <yu.chen.surf@...il.com>
To:	linux-input@...r.kernel.org
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Benjamin Tissoires <benjamin.tissoires@...hat.com>,
	Jiri Kosina <jkosina@...e.com>,
	Dmitry Vyukov <dvyukov@...gle.com>
Subject: [RFC] Can we bypass the timeout when resetting Synaptics device?

Hi All,
Currently I'm doing some tunings on the speed of suspend/resume,
it looks like my serio driver tooks a 200ms to finish, which is
too long:

[ 1120.255783] calling  serio0+ @ 2764, parent: i8042
[ 1120.452976] call serio0+ returned 0 after 192472 usecs

So further investigation shows that the time cost is in
drivers/input/serio/libps2.c: __ps2_command

        /*
         * Some devices (Synaptics) peform the reset before
         * ACKing the reset command, and so it can take a long
         * time before the ACK arrives.
         */
        if (ps2_sendbyte(ps2dev, command & 0xff,
                         command == PS2_CMD_RESET_BAT ? 1000 : 200)) {
                serio_pause_rx(ps2dev->serio);
                goto out_reset_flags;
        }
If I understand correctly, if it is a Synaptics device, then we have to wait
at least 200ms for ATKBD_CMD_RESET_DEF, although this device has already
been reset.

So my question is, could we add flags to distinguish Synaptics device, and
if it is a Synaptics device, just do not wait that long time and
return after the command
has been sent out?


thanks,
Yu