On 4/6/21 2:09 PM, Konstantin Aladyshev wrote: > Thanks for the answer! > Sorry for the confusion, by the "CPU is off" I meant "CPU is present, > but currently it is in the powered off state". > Therefore it is not possible to put these checks only in a probe > function. And I don't know either if it is a good idea to cache > config/min/max values. > > I use this driver on an OpenBMC system, which uses other software > rather than lm-sensors utility. I guess that is why my priorities are > shifted. > > By the way, I've noticed that the mutex check is absent in a > SBTSI_REG_CONFIG read call both in the original driver version and in > my patch, is this an error? > What do you mean with "mutex check" ? Thanks, Guenter > Best regards, > Konstantin Aladyshev > > > On Tue, Apr 6, 2021 at 11:09 PM Guenter Roeck <linux@xxxxxxxxxxxx> wrote: >> >> On 4/6/21 12:20 PM, Konstantin Aladyshev wrote: >>> Thanks for the comment. >>> Yes, you are correct, this patch adds an extra 'i2c_smbus_read_byte_data' call for the temp_max/temp_min reads. >>> I guess I did that intentionally because I just wanted to keep the restructured code concise. After all I thought, 'temp_input' generally is read more often than 'temp_max/temp_min'. >>> As I understand now, it seems like it is not acceptable. Therefore could you point me in the right direction about what I should do? >>> Should I just stick with the original driver version and simply add two more i2c call checks for the first operations for min/max? >>> >> >> Correct, it is not acceptable. A normal use case for hwmon devices is to use the "sensors" >> command which _will_ read all attributes. i2c reads are expensive, and unnecessary read >> operations should be avoided. >> >> There are several ways to solve the problem. Checking return values after each >> read is the simple option. There are other possibilities, such as reading the limits >> and the read order only once during probe, but I don't know enough about the >> hardware to suggest a more sophisticated solution. For example, I don't know >> what "CPU is off" means. Offline ? Not present ? If it means "not present", >> or if the status is permanent, the condition should be handled in the is_visible >> function (or the driver should not be instantiated in the first place). >> Otherwise, the code should possibly return -ENODATA instead of -ETIMEDOUT >> on error. But, again, I can not really suggest a better solution since >> I don't know enough (nothing, actually) about the hardware (and the public >> part of the SBTSI specification doesn't say anything about expected behavior >> for offline CPUs or CPU cores). >> >> What I did find, though, is that the driver does not implement temperature >> offset support, and it that doesn't support reporting alerts. I'd have assumed >> this to be more important than optimizing error handling, but that is just >> my personal opinion. >> >> Thanks, >> Guenter >> >>> Best regards, >>> Konstantin Aladyshev >>> >>> >>> On Tue, Apr 6, 2021 at 9:42 PM Guenter Roeck <linux@xxxxxxxxxxxx <mailto:linux@xxxxxxxxxxxx>> wrote: >>> >>> On 4/6/21 11:16 AM, Konstantin Aladyshev wrote: >>> > SBTSI sensors don't work when the CPU is off. >>> > In this case every 'i2c_smbus_read_byte_data' function would fail >>> > by a timeout. >>> > Currently temp1_max/temp1_min file reads can cause two such timeouts >>> > for every read. >>> > Restructure code so there will be no more than one timeout for every >>> > read operation. >>> > >>> > Signed-off-by: Konstantin Aladyshev <aladyshev22@xxxxxxxxx <mailto:aladyshev22@xxxxxxxxx>> >>> > --- >>> > Changes in v2: >>> > - Fix typo in a commit message >>> > - Don't swap temp_int/temp_dec checks at the end of the 'sbtsi_read' function >>> > >>> >>> This doesn't explain the reason for the extra read operation for >>> limits. Preventing a second read in error cases is not an argument >>> for adding an extra read for non-error cases. >>> >>> Guenter >>> >>> > drivers/hwmon/sbtsi_temp.c | 55 +++++++++++++++++++------------------- >>> > 1 file changed, 27 insertions(+), 28 deletions(-) >>> > >>> > diff --git a/drivers/hwmon/sbtsi_temp.c b/drivers/hwmon/sbtsi_temp.c >>> > index e35357c48b8e..4ae48635bb31 100644 >>> > --- a/drivers/hwmon/sbtsi_temp.c >>> > +++ b/drivers/hwmon/sbtsi_temp.c >>> > @@ -74,48 +74,47 @@ static int sbtsi_read(struct device *dev, enum hwmon_sensor_types type, >>> > u32 attr, int channel, long *val) >>> > { >>> > struct sbtsi_data *data = dev_get_drvdata(dev); >>> > + u8 temp_int_reg, temp_dec_reg; >>> > s32 temp_int, temp_dec; >>> > int err; >>> > >>> > switch (attr) { >>> > case hwmon_temp_input: >>> > - /* >>> > - * ReadOrder bit specifies the reading order of integer and >>> > - * decimal part of CPU temp for atomic reads. If bit == 0, >>> > - * reading integer part triggers latching of the decimal part, >>> > - * so integer part should be read first. If bit == 1, read >>> > - * order should be reversed. >>> > - */ >>> > - err = i2c_smbus_read_byte_data(data->client, SBTSI_REG_CONFIG); >>> > - if (err < 0) >>> > - return err; >>> > - >>> > - mutex_lock(&data->lock); >>> > - if (err & BIT(SBTSI_CONFIG_READ_ORDER_SHIFT)) { >>> > - temp_dec = i2c_smbus_read_byte_data(data->client, SBTSI_REG_TEMP_DEC); >>> > - temp_int = i2c_smbus_read_byte_data(data->client, SBTSI_REG_TEMP_INT); >>> > - } else { >>> > - temp_int = i2c_smbus_read_byte_data(data->client, SBTSI_REG_TEMP_INT); >>> > - temp_dec = i2c_smbus_read_byte_data(data->client, SBTSI_REG_TEMP_DEC); >>> > - } >>> > - mutex_unlock(&data->lock); >>> > + temp_int_reg = SBTSI_REG_TEMP_INT; >>> > + temp_dec_reg = SBTSI_REG_TEMP_DEC; >>> > break; >>> > case hwmon_temp_max: >>> > - mutex_lock(&data->lock); >>> > - temp_int = i2c_smbus_read_byte_data(data->client, SBTSI_REG_TEMP_HIGH_INT); >>> > - temp_dec = i2c_smbus_read_byte_data(data->client, SBTSI_REG_TEMP_HIGH_DEC); >>> > - mutex_unlock(&data->lock); >>> > + temp_int_reg = SBTSI_REG_TEMP_HIGH_INT; >>> > + temp_dec_reg = SBTSI_REG_TEMP_HIGH_DEC; >>> > break; >>> > case hwmon_temp_min: >>> > - mutex_lock(&data->lock); >>> > - temp_int = i2c_smbus_read_byte_data(data->client, SBTSI_REG_TEMP_LOW_INT); >>> > - temp_dec = i2c_smbus_read_byte_data(data->client, SBTSI_REG_TEMP_LOW_DEC); >>> > - mutex_unlock(&data->lock); >>> > + temp_int_reg = SBTSI_REG_TEMP_LOW_INT; >>> > + temp_dec_reg = SBTSI_REG_TEMP_LOW_DEC; >>> > break; >>> > default: >>> > return -EINVAL; >>> > } >>> > >>> > + /* >>> > + * ReadOrder bit specifies the reading order of integer and >>> > + * decimal part of CPU temp for atomic reads. If bit == 0, >>> > + * reading integer part triggers latching of the decimal part, >>> > + * so integer part should be read first. If bit == 1, read >>> > + * order should be reversed. >>> > + */ >>> > + err = i2c_smbus_read_byte_data(data->client, SBTSI_REG_CONFIG); >>> > + if (err < 0) >>> > + return err; >>> > + >>> > + mutex_lock(&data->lock); >>> > + if (err & BIT(SBTSI_CONFIG_READ_ORDER_SHIFT)) { >>> > + temp_dec = i2c_smbus_read_byte_data(data->client, temp_dec_reg); >>> > + temp_int = i2c_smbus_read_byte_data(data->client, temp_int_reg); >>> > + } else { >>> > + temp_int = i2c_smbus_read_byte_data(data->client, temp_int_reg); >>> > + temp_dec = i2c_smbus_read_byte_data(data->client, temp_dec_reg); >>> > + } >>> > + mutex_unlock(&data->lock); >>> > >>> > if (temp_int < 0) >>> > return temp_int; >>> > >>> >>
