Messages in this thread | | | Date | Tue, 27 Jan 2015 20:06:13 -0800 | From | Guenter Roeck <> | Subject | Re: [lm-sensors] [PATCH] hwmon: (ads7828) Make sample interval configurable |
| |
On 01/27/2015 02:34 PM, Jean Delvare wrote: > On Tue, 27 Jan 2015 12:05:53 -0800, Guenter Roeck wrote: >> On Tue, Jan 27, 2015 at 08:54:34PM +0100, Robert Rosengren wrote: >>> Guenter and Jean, >>> >>> To sum up, my problems was related my kernel and hardware configuration, and it now works. Many thanks for your input! >>> >>> However, the values retrieved from hwmon sysfs is not the same as before the regmap patch. Guenter, the byte swap for the regval retrieved by regmap_read. In what order is the bits returned from that function, because it seems as if I disabled that code I get values as I expect (i.e. before the regmap patch). >>> >> Trying to understand. Are you saying everything works as expected >> if you keep byte_swap set to false ? >> >> That might well be, though it might mean that regmap has a bug >> in how it treats i2c word read operations. I'll have to look into it >> some more. > > Remember that SMBus specifies that the LSB comes first (and i2c-core > implement things that way) while real I2C devices typically send the MSB > first. This has always caused confusion. This is why a lot of drivers > need byte-swapping. >
regmap specifies "normal" i2c accesses as MSB first. When SMBus accesses are used, it specifies LSB first. I guess that means that regmap assumes the more common case of MSB first, meaning the driver would not need a byte swap since the chip reports data with MSB first.
I just hope I interpret it correctly this time.
There is also a configuration flag "val_format_endian" which can be set to REGMAP_ENDIAN_BIG or REGMAP_ENDIAN_LITTLE. Maybe that can be used as well if needed. Either case I'll wait for the samples before I send an updated version of the patch.
Guenter
| |