2021-12-21 10:48:06

by Leo L. Schwab

Subject: [PATCH v2] Input: spaceball - fix parsing of movement data packets

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...

Signed-off-by: Leo L. Schwab <[email protected]>
---
Changes in v2:
- Coding style changes requested by <[email protected]>.

drivers/input/joystick/spaceball.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/input/joystick/spaceball.c b/drivers/input/joystick/spaceball.c
index 429411c6c0a8..10e09c86e067 100644
--- a/drivers/input/joystick/spaceball.c
+++ b/drivers/input/joystick/spaceball.c
@@ -19,6 +19,7 @@
#include <linux/module.h>
#include <linux/input.h>
#include <linux/serio.h>
+#include <asm/unaligned.h>

#define DRIVER_DESC "SpaceTec SpaceBall 2003/3003/4000 FLX driver"

@@ -74,10 +75,16 @@ 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++)
+ data += 3;
+ for (i = 0; i < ARRAY_SIZE(spaceball_axes); ++i) {
input_report_abs(dev, spaceball_axes[i],
- (__s16)((data[2 * i + 3] << 8) | data[2 * i + 2]));
+ (__s16)get_unaligned_be16(&data[i * 2]));
+ }
break;

case 'K': /* Button data */
--
2.34.1

2021-12-31 05:10:48

by Dmitry Torokhov

Subject: Re: [PATCH v2] Input: spaceball - fix parsing of movement data packets

On Tue, Dec 21, 2021 at 02:16:31AM -0800, 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...
>
> Signed-off-by: Leo L. Schwab <[email protected]>

Applied, thank you.

--
Dmitry