linux/drivers/hwmon/tmp102.c

423 lines
9.8 KiB

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 157 Based on 3 normalized pattern(s): this program is free software you can redistribute it and or modify it under the terms of the gnu general public license as published by the free software foundation either version 2 of the license or at your option any later version this program is distributed in the hope that it will be useful but without any warranty without even the implied warranty of merchantability or fitness for a particular purpose see the gnu general public license for more details this program is free software you can redistribute it and or modify it under the terms of the gnu general public license as published by the free software foundation either version 2 of the license or at your option any later version [author] [kishon] [vijay] [abraham] [i] [kishon]@[ti] [com] this program is distributed in the hope that it will be useful but without any warranty without even the implied warranty of merchantability or fitness for a particular purpose see the gnu general public license for more details this program is free software you can redistribute it and or modify it under the terms of the gnu general public license as published by the free software foundation either version 2 of the license or at your option any later version [author] [graeme] [gregory] [gg]@[slimlogic] [co] [uk] [author] [kishon] [vijay] [abraham] [i] [kishon]@[ti] [com] [based] [on] [twl6030]_[usb] [c] [author] [hema] [hk] [hemahk]@[ti] [com] this program is distributed in the hope that it will be useful but without any warranty without even the implied warranty of merchantability or fitness for a particular purpose see the gnu general public license for more details extracted by the scancode license scanner the SPDX license identifier GPL-2.0-or-later has been chosen to replace the boilerplate/reference in 1105 file(s). Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Allison Randal <allison@lohutok.net> Reviewed-by: Richard Fontana <rfontana@redhat.com> Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org> Cc: linux-spdx@vger.kernel.org Link: https://lkml.kernel.org/r/20190527070033.202006027@linutronix.de Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2019-05-27 08:55:06 +02:00
hwmon: (tmp102) Force wait for conversion time for the first valid data TMP102 works based on conversions done periodically. However, as per the TMP102 data sheet[1] the first conversion is triggered immediately after we program the configuration register. The temperature data registers do not reflect proper data until the first conversion is complete (in our case HZ/4). The driver currently sets the last_update to be jiffies - HZ, just after the configuration is complete. When TMP102 driver registers with the thermal framework, it immediately tries to read the sensor temperature data. This takes place even before the conversion on the TMP102 is complete and results in an invalid temperature read. Depending on the value read, this may cause thermal framework to assume that a critical temperature event has occurred and attempts to shutdown the system. Instead of causing an invalid mid-conversion value to be read erroneously, we mark the last_update to be in-line with the current jiffies. This allows the tmp102_update_device function to skip update until the required conversion time is complete. Further, we ensure to return -EAGAIN result instead of returning spurious temperature (such as 0C) values to the caller to prevent any wrong decisions made with such values. NOTE: this allows the read functions not to be blocking and allows the callers to make the decision if they would like to block or try again later. At least the current user(thermal) seems to handle this by retrying later. A simpler alternative approach could be to sleep in the probe for the duration required, but that will result in latency that is undesirable and delay boot sequence un-necessarily. [1] http://www.ti.com/lit/ds/symlink/tmp102.pdf Cc: Eduardo Valentin <edubezval@gmail.com> Reported-by: Aparna Balasubramanian <aparnab@ti.com> Reported-by: Elvita Lobo <elvita@ti.com> Reported-by: Yan Liu <yan-liu@ti.com> Signed-off-by: Nishanth Menon <nm@ti.com> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
2015-12-01 10:10:21 -06:00
hwmon: (tmp102) Force wait for conversion time for the first valid data TMP102 works based on conversions done periodically. However, as per the TMP102 data sheet[1] the first conversion is triggered immediately after we program the configuration register. The temperature data registers do not reflect proper data until the first conversion is complete (in our case HZ/4). The driver currently sets the last_update to be jiffies - HZ, just after the configuration is complete. When TMP102 driver registers with the thermal framework, it immediately tries to read the sensor temperature data. This takes place even before the conversion on the TMP102 is complete and results in an invalid temperature read. Depending on the value read, this may cause thermal framework to assume that a critical temperature event has occurred and attempts to shutdown the system. Instead of causing an invalid mid-conversion value to be read erroneously, we mark the last_update to be in-line with the current jiffies. This allows the tmp102_update_device function to skip update until the required conversion time is complete. Further, we ensure to return -EAGAIN result instead of returning spurious temperature (such as 0C) values to the caller to prevent any wrong decisions made with such values. NOTE: this allows the read functions not to be blocking and allows the callers to make the decision if they would like to block or try again later. At least the current user(thermal) seems to handle this by retrying later. A simpler alternative approach could be to sleep in the probe for the duration required, but that will result in latency that is undesirable and delay boot sequence un-necessarily. [1] http://www.ti.com/lit/ds/symlink/tmp102.pdf Cc: Eduardo Valentin <edubezval@gmail.com> Reported-by: Aparna Balasubramanian <aparnab@ti.com> Reported-by: Elvita Lobo <elvita@ti.com> Reported-by: Yan Liu <yan-liu@ti.com> Signed-off-by: Nishanth Menon <nm@ti.com> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
2015-12-01 10:10:21 -06:00