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Commit e70d13f7 authored by Sean Young's avatar Sean Young Committed by Mauro Carvalho Chehab
Browse files

media: imon_raw: simplify and explain bit operations 



This code needs some explanation.

Signed-off-by: default avatarSean Young <sean@mess.org>
Signed-off-by: default avatarMauro Carvalho Chehab <mchehab+samsung@kernel.org>
parent 1b09a2af

drivers/media/rc/imon_raw.c

+34 −9
Original line number Diff line number Diff line
@@ -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);

	}
@@ -72,7 +98,6 @@ static void imon_ir_rx(struct urb *urb) 


	switch (urb->status) {

	case 0:

		if (imon->ir_buf[7] != 0xff)

		imon_ir_data(imon);

		break;

	case -ECONNRESET:
@@ -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);