From: Dmitry Torokhov <dmitry.torokhov@gmail.com>
To: "Leo L. Schwab" <ewhac@ewhac.org>
Cc: linux-input@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Input: spaceball - fix parsing of movement data packets
Date: Mon, 20 Dec 2021 00:59:21 -0800 [thread overview]
Message-ID: <YcBF6bnRjYRMp2Cq@google.com> (raw)
In-Reply-To: <20210727040625.2159196-1-ewhac@ewhac.org>
Hi Leo,
On Mon, Jul 26, 2021 at 09:06:24PM -0700, Leo L. Schwab wrote:
> The spaceball.c module was not properly parsing the movement reports
> coming from the device. The code read axis data as signed 16-bit
> little-endian values starting at offset 2.
>
> In fact, axis data in Spaceball movement reports are signed 16-bit
> big-endian values starting at offset 3. This was determined first by
> visually inspecting the data packets, and later verified by consulting:
> http://spacemice.org/pdf/SpaceBall_2003-3003_Protocol.pdf
>
> If this ever worked properly, it was in the time before Git...
Thank you for the patch.
>
> Signed-off-by: Leo L. Schwab <ewhac@ewhac.org>
> ---
> drivers/input/joystick/spaceball.c | 16 +++++++++++++---
> 1 file changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/input/joystick/spaceball.c b/drivers/input/joystick/spaceball.c
> index 429411c6c0a8..43bfb3d2fa8a 100644
> --- a/drivers/input/joystick/spaceball.c
> +++ b/drivers/input/joystick/spaceball.c
> @@ -74,10 +74,20 @@ static void spaceball_process_packet(struct spaceball* spaceball)
> switch (spaceball->data[0]) {
>
> case 'D': /* Ball data */
> + /*
> + * Skip first three bytes; read six axes worth of data.
> + * Axis values are signed 16-bit big-endian.
> + */
> if (spaceball->idx != 15) return;
> - for (i = 0; i < 6; i++)
> - input_report_abs(dev, spaceball_axes[i],
> - (__s16)((data[2 * i + 3] << 8) | data[2 * i + 2]));
> + data += 3;
> + for (i = 0;
> + i < ARRAY_SIZE(spaceball_axes);
> + ++i, data += sizeof(__s16)) {
> + input_report_abs(
> + dev,
> + spaceball_axes[i],
> + (__s16)((data[0] << 8) | data[1]));
> + }
Could we write
for (i == 0; i < ARRAY_SIZE(spaceball_axes); i++)
input_report_abs(dev, spaceball_axes[i],
(__s16)(get_unaligned_be16(&data[i * 2]);
instead?
Thanks!
--
Dmitry
next prev parent reply other threads:[~2021-12-20 8:59 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-27 4:06 [PATCH] Input: spaceball - fix parsing of movement data packets Leo L. Schwab
2021-12-16 8:58 ` Leo L. Schwab
2021-12-20 8:59 ` Dmitry Torokhov [this message]
2021-12-21 10:00 ` Leo L. Schwab
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