Messages in this thread | | | Subject | Re: [PATCH v2] hwmon: ina2xx: allow for actual measurement bandwidth above 160 Hz | From | Marc Titinger <> | Date | Tue, 20 Oct 2015 15:17:33 +0200 |
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On 20/10/2015 14:54, Guenter Roeck wrote: > On 10/20/2015 01:20 AM, Marc Titinger wrote: >> With the current implementation, the driver will prevent a readout at a >> pace faster than the default conversion time (2ms) times the averaging >> setting, min AVG being 1:1. >> >> Any sysfs "show" read access from the client app faster than 500 Hz >> will be >> 'cached' by the driver, but actually since do_update reads all 8 >> registers, >> the best achievable measurement rate is roughly 8*800 us (for the time >> spent in i2c-core) i.e. <= 156Hz with Beagle Bone Black. >> >> This change set uses a register mask to allow for the readout of a single >> i2c register at a time. Furthermore, performing subsequent reads on the >> same register will make use of the ability of the i2c chip to retain the >> last reg offset, hence use a shorter i2c message (roughly 400us >> instead of >> 800us spent in i2c-core.c). >> > That doesn't work. There could be accesses from other sources (such as > through > i2c-dev, or in multi-master systems) between two reads.
Re-setting the register address with each read transaction will not prevent another master to change the configuration in your back, in this case. That sounds like a general issue of concurrent clients for one device, this is beyond just reading one register IMO.
> >> The best readout rate for a single measurement is now around 2kHz. And >> for >> four measurements around (1/(4*800us) = 312 Hz. Since for any readout >> rate >> faster than 160 Hz the interval is set by the i2c transactions >> completion, >> the 'last-update' anti-flooding code will not have a limiting effect in >> practice. Hence I also remove the elapsed time checking in the hwmon >> driver >> for ina2xx. >> >> To summarize, the patch provides a max bandwidth improvement with hwmon >> client apps from ~160 Hz to ~320 Hz, and better in single-channel >> polling mode. >> > Overall your patch pretty much re-implements regmap. Since you drop > caching, > it is also unnecessary to read all registers at a time, so you can just use > a function to read _one_ register and returns its value (with retries). > Or use regmap. Either case, do_update() and ina2xx_update_device() are no > longer needed. Agreed.
> > If you want to convert the driver to regmap, just look for 'regmap' in > drivers/hwmon for examples.
Fair enough, but based on your comments, I may look into an iio driver instead for this device, given our application, rather than 'twisting' the hwmon interface.
Cheers, Marc.
> > Guenter >
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