Hi Jonathan, On Sun, Jul 15, 2018 at 10:10:36AM +0100, Jonathan Cameron wrote: > On Sat, 14 Jul 2018 13:03:42 +0530 > Himanshu Jha <himanshujha199...@gmail.com> wrote: > > > Hi David, > > > > On Fri, Jul 13, 2018 at 01:42:35PM -0700, David Frey wrote: > > > Hi Himanshu Jha, > > > > > > First a bit of background. I'm working on a device which will contain a > > > bme680 sensor. A colleague of mine started work on a Linux kernel driver > > > for the chip a little while ago. The (WIP) driver can be found here: > > > https://github.com/mangOH/mangOH/tree/master/linux_kernel_modules/bme680 > > > > Great! > > > > > This driver is written targeting an older kernel (3.18.x) because that's > > > the > > > kernel we're stuck on for now. Rather than writing the driver from > > > scratch, > > > what we did was write the Linux kernel driver as a wrapper around the > > > Bosch > > > code. My theory at the time was that Bosch made the chip, so they > > > probably > > > know what they're doing when it comes to writing a driver library. After > > > having looked at the code in more detail, I'm less confident that our > > > approach was the best one. I'm not attempting to upstream the driver > > > built > > > by my colleague and I'm not trying to request review of this code either. > > > I > > > simply want to make you aware of it so that you can look at it to get some > > > ideas. > > > > Thanks for taking your time to review. > > > > > I have included a number of comments on your driver below. Keep up the > > > good > > > work! > > > > > > >+++ b/drivers/iio/chemical/bme680.h > > > >@@ -0,0 +1,99 @@ > > > >+/* SPDX-License-Identifier: GPL-2.0 */ > > > >+#ifndef BME680_H_ > > > >+#define BME680_H_ > > > >+ > > > >+#define BME680_REG_CHIP_I2C_ID 0xD0 > > > >+#define BME680_REG_CHIP_SPI_ID 0x50 > > > >+#define BME680_CHIP_ID_VAL 0x61 > > > Try to be consistent with the indenting of the defines. I think this > > > would > > > be clearest: > > > #define BME680_REG_X 0x00 > > > #define BME680_X_FOO_EN_MASK BIT(0) > > > #define BME680_X_BAR_MASK GENMASK(3, 1) > > > #define BME680_BAR_VAL1 3 > > > #define BME680_BAR_VAL2 7 > > > > > > This way the register, field definition and field values are all visually > > > distinctive. > > > > I have used this pattern everywhere where applicable. But not applied > > for *_VAL, would definitely follow this up. > > > > > >+#define BME680_REG_SOFT_RESET 0xE0 > > > The datasheet says that the soft reset register differs for I2C and SPI. > > > For I2C it is 0xE0 and for SPI it is 0x60 when page 0 is selected. > > > > That's really a stupid mistake :( > > I have exported these individual initialization code in the I2C & SPI > > drivers respectively but it slipped my mind somehow. This device has > > peculiar characteristics in register addressing. > > > > I will correct this in next version. > > > > > >+#define BME680_CMD_SOFTRESET 0xB6 > > > >+#define BME680_REG_STATUS 0x73 > > > >+#define BME680_SPI_MEM_PAGE_BIT BIT(4) > > > >+#define BME680_SPI_MEM_PAGE_1_VAL 1 > > > >+ > > > >+#define BME680_OSRS_TEMP_X(osrs_t) ((osrs_t) << 5) > > > >+#define BME680_OSRS_PRESS_X(osrs_p) ((osrs_p) << 2) > > > >+#define BME680_OSRS_HUMID_X(osrs_h) ((osrs_h) << 0) > > > You could use the FIELD_PREP macro from <linux/bitfield.h> to eliminate > > > the > > > need for these macros. For example: > > > ctrl_meas_reg = FIELD_PREP(BME680_OSRS_TEMP_MASK, temp_val) | > > > FIELD_PREP(BME680_OSRS_PRESS_MASK, press_val) | > > > FIELD_PREP(BME880_MODE_MASK, mode_val); > > > > Ah, yes! I didn't knew about these magic macros. It will remove some > > log2() computation hacks from my code. > > > > > >+ > > > >+#define BME680_REG_TEMP_MSB 0x22 > > > >+#define BME680_REG_PRESS_MSB 0x1F > > > >+#define BM6880_REG_HUMIDITY_MSB 0x25 > > > >+#define BME680_REG_GAS_MSB 0x2A > > > >+#define BME680_REG_GAS_R_LSB 0x2B > > > >+#define BME680_GAS_STAB_BIT BIT(4) > > > >+ > > > >+#define BME680_REG_CTRL_HUMIDITY 0x72 > > > >+#define BME680_OSRS_HUMIDITY_MASK GENMASK(2, 0) > > > >+ > > > >+#define BME680_REG_CTRL_MEAS 0x74 > > > >+#define BME680_OSRS_TEMP_MASK GENMASK(7, 5) > > > >+#define BME680_OSRS_PRESS_MASK GENMASK(4, 2) > > > >+#define BME680_MODE_MASK GENMASK(1, 0) > > > >+ > > > >+#define BME680_MODE_FORCED BIT(0) > > > >+#define BME680_MODE_SLEEP 0 > > > This should be: > > > #define BME680_MODE_SLEEP 0 > > > #define BME680_MODE_FORCED 1 > > > > Yes, this is much clearer and removes ambiguity. > > > > > >+/* Taken from Bosch BME680 API */ > > > > > > I think there should be a link to the Bosch code > > > (https://github.com/BoschSensortec/BME680_driver/) somewhere within the > > > comments of this file. Maybe it belongs at the top of this file? > > > > I planned to add: > > https://github.com/BoschSensortec/BME680_driver/blob/63bb5336db4659519860832be2738c685133aa33/bme680.c#L876 > > to here and likewise to other compensate functions. > > But these links may change(if somehow they plan to migrate to Gitlab), > > long lines are not welcomed. > > Looks like github does the same trick kernel.org does in allowing shortened > hashes.
$ git log --abbrev-commit ... > I think > > https://github.com/BoschSensortec/BME680_driver/blob/63bb5336/bme680.c#L876 > Is the same thing and under 80 chars (just) :) Ah, yes :) Perfect! > > You could also notice that I haven't included datasheet link at the top > > of this file. Well, most of the companies change the links when releasing > > the new Revision(Rev. A,B,...) so it is likely that the link would be > > dead/old lying at the top of source. > > Even though this happens, it's better to have something than nothing > perhaps. Sure! Will add both links in next version. > > Yes, we can do that but, for a while, I am following my GSoC proposal > > timeline. And I have planned these check_bits function later, but since > > this check_bits function was imperative in gas sensing, therefore I > > included them now. > > > > My plan in incremental changes and this patch is kindof minimal. I have > > tested the sensor several times and found no errors in readings for > > T P H G readings so far. > > > > The problem arises that this sensor is made to work in a T->P->H->G > > fashion and every channel is mostly dependent on the other. And IIO > > driver design pattern isn't the best choice it. You can't just take a > > single channel readings by running Bosch Code because it is not designed > > like that. > > > > For instance: we need t_fine values for pressure/humidity compensation > > functions which we only get when reading temperature. So, you need to > > run the temperaure cycle if you need pressure/humidity values. And this > > is what I did by doing a dummy read_temp(data, NULL, NULL) to get the t_fine > > value. > > This pattern isn't that unusual in devices. Normally you do it pretty > much the way you have. The sysfs interface in IIO is just interested > in data presentation, we don't care what you have to do to get it ;) OK. I agree, but will create a new thread for some clarification/rectification of IIO core. > This will fit much better when doing buffered interfaces anyway which > naturally grab sets of channels. Yes, I think so it work better in that way. Also, for industrial use I think buffered interface is a better option. > > Thanks you so much for the feedback, David! :) > > > > And if at some point I have said something stupid, then please forgive me. > > > > I am a 3rd year undergrad student and started with IIO few months back, and > > not a Bosch driver developer ;) > > > Going well so far ;) Thanks Jonathan again :) Well it is better to hint developers that you're a student, else I had a discussion in the past where some senior developer was explaining me about CPU profiling (I don't remember exactly) and it didn't even hit me for the next two weeks ;) But I would like David to review the patches in the next version too. -- Himanshu Jha Undergraduate Student Department of Electronics & Communication Guru Tegh Bahadur Institute of Technology
