Hi Nicolin, On Wed, Sep 26, 2018 at 11:20:06AM -0700, Nicolin Chen wrote: > On Wed, Sep 26, 2018 at 05:34:53AM -0700, Guenter Roeck wrote: > > Hi Nicolin, > > > > On 09/25/2018 11:42 PM, Nicolin Chen wrote: > > > The hwmon sysfs ABI supports powerX_input and powerX_crit. This > > > can ease user space programs who care more about power in total > > > than voltage or current individually. > > > > > > So this patch adds these two sysfs nodes for INA3221 driver. > > > Ah, sorry, we can't do that. The sysfs nodes are for chips providing power > > registers, not for kernel drivers to provide calculations based on voltage > > and current measurements. > > Hmm..I saw ina2xx.c and ltc4215.c are doing similar calculations... > ina2xx.c doesn't; the chips supported by the driver do have a register reporting the power (0x03). ltc4215.c was not reviewed by a hwmon maintainer. I think I mentioned before that you can find anything you want in the Linux kernel. That doesn't make it right. > > Basic guideline is that we report what is there, not some calculation based > > on it. > > I could feel the back thoughts behind the guideline, but this does > give user space programs some trouble -- I have a few programs that > were used to read ina2xx driver which provides power nodes, but now > those programs will have to implement another function to read the > voltage and current separately to do further calculations. > > Do you know any better solution for this situation? > Userspace simply must not assume that power attributes exist and calculate it from voltage and current attributes if needed. > > This is even more true for power limits: We can not assume that the power limit > > is (max voltage * max current). or (current voltage * max_current), or anything > > else. We simply don't have the knowledge to make that assumption. > > I agree that power limit is a bit tricky here as the voltage could > change depending on the user space, Yes, I assumed that users who > set_power() should be aware of it (whether fixed or dynamical) so > as to decide to configure power limit or just current limit. > You just can not make any such assumptions, sorry. Limit attributes absolutely must be reflected in hardware. Thanks, Guenter
