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Subject: media: imon_raw: simplify and explain bit operations
Author: Sean Young <s...@mess.org>
Date: Fri Aug 9 18:47:41 2019 -0300
This code needs some explanation.
Signed-off-by: Sean Young <s...@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+sams...@kernel.org>
drivers/media/rc/imon_raw.c | 43 ++++++++++++++++++++++++++++++++++---------
1 file changed, 34 insertions(+), 9 deletions(-)
---
diff --git a/drivers/media/rc/imon_raw.c b/drivers/media/rc/imon_raw.c
index 25e56c5b13c0..e6723993b466 100644
--- a/drivers/media/rc/imon_raw.c
+++ b/drivers/media/rc/imon_raw.c
@@ -14,7 +14,7 @@ struct imon {
struct device *dev;
struct urb *ir_urb;
struct rc_dev *rcdev;
- u8 ir_buf[8] __aligned(__alignof__(u64));
+ __be64 ir_buf;
char phys[64];
};
@@ -29,14 +29,35 @@ struct imon {
static void imon_ir_data(struct imon *imon)
{
struct ir_raw_event rawir = {};
- u64 d = be64_to_cpup((__be64 *)imon->ir_buf) >> 24;
+ u64 data = be64_to_cpu(imon->ir_buf);
+ u8 packet_no = data & 0xff;
int offset = 40;
int bit;
- dev_dbg(imon->dev, "data: %*ph", 8, imon->ir_buf);
+ if (packet_no == 0xff)
+ return;
+
+ dev_dbg(imon->dev, "data: %*ph", 8, &imon->ir_buf);
+
+ /*
+ * Only the first 5 bytes contain IR data. Right shift so we move
+ * the IR bits to the lower 40 bits.
+ */
+ data >>= 24;
do {
- bit = fls64(d & (BIT_ULL(offset) - 1));
+ /*
+ * Find highest set bit which is less or equal to offset
+ *
+ * offset is the bit above (base 0) where we start looking.
+ *
+ * data & (BIT_ULL(offset) - 1) masks off any unwanted bits,
+ * so we have just bits less than offset.
+ *
+ * fls will tell us the highest bit set plus 1 (or 0 if no
+ * bits are set).
+ */
+ bit = fls64(data & (BIT_ULL(offset) - 1));
if (bit < offset) {
dev_dbg(imon->dev, "pulse: %d bits", offset - bit);
rawir.pulse = true;
@@ -49,7 +70,12 @@ static void imon_ir_data(struct imon *imon)
offset = bit;
}
- bit = fls64(~d & (BIT_ULL(offset) - 1));
+ /*
+ * Find highest clear bit which is less than offset.
+ *
+ * Just invert the data and use same trick as above.
+ */
+ bit = fls64(~data & (BIT_ULL(offset) - 1));
dev_dbg(imon->dev, "space: %d bits", offset - bit);
rawir.pulse = false;
@@ -59,7 +85,7 @@ static void imon_ir_data(struct imon *imon)
offset = bit;
} while (offset > 0);
- if (imon->ir_buf[7] == 0x0a) {
+ if (packet_no == 0x0a) {
ir_raw_event_set_idle(imon->rcdev, true);
ir_raw_event_handle(imon->rcdev);
}
@@ -72,8 +98,7 @@ static void imon_ir_rx(struct urb *urb)
switch (urb->status) {
case 0:
- if (imon->ir_buf[7] != 0xff)
- imon_ir_data(imon);
+ imon_ir_data(imon);
break;
case -ECONNRESET:
case -ENOENT:
@@ -129,7 +154,7 @@ static int imon_probe(struct usb_interface *intf,
imon->dev = &intf->dev;
usb_fill_int_urb(imon->ir_urb, udev,
usb_rcvintpipe(udev, ir_ep->bEndpointAddress),
- imon->ir_buf, sizeof(imon->ir_buf),
+ &imon->ir_buf, sizeof(imon->ir_buf),
imon_ir_rx, imon, ir_ep->bInterval);
rcdev = devm_rc_allocate_device(&intf->dev, RC_DRIVER_IR_RAW);
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