[media] cx25840: Prevent device probe failure due to volume control ERANGE error [Linux 2.6.37]

This Linux kernel change "[media] cx25840: Prevent device probe failure due to volume control ERANGE error" is included in the Linux 2.6.37 release. This change is authored by Andy Walls <awalls [at] md.metrocast.net> on Sun Dec 5 19:42:30 2010 -0300. The commit for this change in Linux stable tree is f23b795 (patch).

[media] cx25840: Prevent device probe failure due to volume control ERANGE error

This patch fixes a regression that crept into 2.6.36.

The volume control scale in the cx25840 driver has an unusual mapping
from register values to v4l2 volume control values.  Enforce the mapping
limits, so that the default volume control setting does not fall out of
bounds to prevent the cx25840 module device probe from failing.

Signed-off-by: Andy Walls <[email protected]>
Cc: Hans Verkuil <[email protected]>
Signed-off-by: Mauro Carvalho Chehab <[email protected]>

There are 19 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 drivers/media/video/cx25840/cx25840-core.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/drivers/media/video/cx25840/cx25840-core.c b/drivers/media/video/cx25840/cx25840-core.c
index dfb198d..f164618 100644
--- a/drivers/media/video/cx25840/cx25840-core.c
+++ b/drivers/media/video/cx25840/cx25840-core.c
@@ -1989,8 +1989,23 @@ static int cx25840_probe(struct i2c_client *client,
    v4l2_ctrl_new_std(&state->hdl, &cx25840_ctrl_ops,
            V4L2_CID_HUE, -128, 127, 1, 0);
    if (!is_cx2583x(state)) {
-       default_volume = 228 - cx25840_read(client, 0x8d4);
-       default_volume = ((default_volume / 2) + 23) << 9;
+       default_volume = cx25840_read(client, 0x8d4);
+       /*
+        * Enforce the legacy PVR-350/MSP3400 to PVR-150/CX25843 volume
+        * scale mapping limits to avoid -ERANGE errors when
+        * initializing the volume control
+        */
+       if (default_volume > 228) {
+           /* Bottom out at -96 dB, v4l2 vol range 0x2e00-0x2fff */
+           default_volume = 228;
+           cx25840_write(client, 0x8d4, 228);
+       }
+       else if (default_volume < 20) {
+           /* Top out at + 8 dB, v4l2 vol range 0xfe00-0xffff */
+           default_volume = 20;
+           cx25840_write(client, 0x8d4, 20);
+       }
+       default_volume = (((228 - default_volume) >> 1) + 23) << 9;

        state->volume = v4l2_ctrl_new_std(&state->hdl,
            &cx25840_audio_ctrl_ops, V4L2_CID_AUDIO_VOLUME,

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