From 80c002ddd2e732062e4371314d40515d0b5d8415 Mon Sep 17 00:00:00 2001 From: David Fries Date: Tue, 22 Jan 2008 03:31:39 -0800 Subject: [PATCH] W1: w1_therm.c is flagging 0C etc as invalid The extra rom[0] check is flagging valid temperatures as invalid when there is already a CRC data transmission check. w1_therm_read_bin() if (rom[8] == crc && rom[0]) verdict = 1; Requiring rom[0] to be non-zero will flag as invalid temperature conversions when the low byte is zero, specifically the temperatures 0C, 16C, 32C, 48C, -16C, -32C, and -48C. The CRC check is produced on the device for the previous 8 bytes and is required to ensure the data integrity in transmission. I don't see why the extra check for rom[0] being non-zero is in there. Evgeniy Polyakov didn't know either. Just for a check I unplugged the sensor, executed a temperature conversion, and read the results. The read was all ff's, which also failed the CRC, so it doesn't need to protect against a disconnected sensor. I have more extensive patches in the work, but these two trivial ones will do for today. I would like to hear from people who use the ds2490 USB to one wire dongle. 1 if you would be willing to test the patches as I currently only have the one sensor on a short parisite powered wire, 2 if there is any cheap sources for the ds2490. Signed-off-by: David Fries Acked-by: Evgeniy Polyakov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- drivers/w1/slaves/w1_therm.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/w1/slaves/w1_therm.c b/drivers/w1/slaves/w1_therm.c index feed89e733e4..112f4ec59035 100644 --- a/drivers/w1/slaves/w1_therm.c +++ b/drivers/w1/slaves/w1_therm.c @@ -204,7 +204,7 @@ static ssize_t w1_therm_read_bin(struct kobject *kobj, crc = w1_calc_crc8(rom, 8); - if (rom[8] == crc && rom[0]) + if (rom[8] == crc) verdict = 1; } } -- 2.20.1