On Wed, Feb 17, 2016 at 12:14 PM, Sergei Shtylyov <sergei.shtylyov@xxxxxxxxxxxxxxxxxx> wrote: > On 02/16/2016 11:05 PM, Rob Herring wrote: > >>>>> + - mentor,power : Specifies the maximum current in milliamperes the >>>>> controller can >>>>> + supply in host mode. >>>> >>>> >>>> Still a no for me. Looks like this just sets hcd->power_budget. This >>>> property may not be a regulator, but ultimately the value depends on >>>> some regulator supplying Vbus. Also, given this has nothing to do with >>>> MUSB h/w, however this is described should be generic. >>> >>> >>> >>> I understand your point that the description should be generic. >>> However the USB 2.0 specification does not define any relation between >>> the >>> bMaxPower provided by the device and the actual power control. >>> As far as I understand the value just serves the purpose to raise a flag >>> to >>> the user if the attached device would draw too much power, and not to >>> enable >>> it at all. >> >> >> That won't really work given devices lie. My bus powered USB disk >> enclosure reports something like 10mA. That's pretty good considering >> I have a 5W drive in it. > > >>> Further, the value used by the protocol is not necessarily related to the >>> real current that can be supported. The maximum current supported by the >>> protocol is 510mA. >>> >>> For instance on my development board the real maximum current is limited >>> only by the mains power-supply used. >>> So it cannot even be modelled in the DT as a regulator because the >>> power-supply is not part of the HW and >>> everybody can take a different one. >> >> >> Not part of which h/w? Different for everyone is exactly why Vbus >> supply should be described in DT. > > > I'm afraid you're misunderstanding the nature of VBUS regulator still. > It's a voltage regulator with some maximum value of the current that can be > sourced from it when it's powered (+5 V). The power chip can typically > detect and report the over-current condition inj which case VBUS will be > turned off). Yes, I understand that exactly. I've seen and reviewed a USB circuit or two. You're describing a regulator, I'm saying describe the regulator in DT and Petr is saying that's too complex. >>> So defining a regulator just to store this arbitrary USB 2.0 value is a >>> bit >>> overkill for me. >> >> >> If it is just arbitrary, then put it into the driver. I would do 500mA > > > You clearly misunderstand things. The regulator used depends on the board > design, the driver (or glue in this case) doesn't, it's just SoC specific. > That's why this power budget thing ended up in the platform data in the > first place... The driver needs to be able to query the supply and get the current limit. We have the technology. > >> and be done with it. I'd guess there is nothing real behind the >> current default of 250mA. > > > 500 mA actually, it's multiplied by 2. Ok. For 2 ports? In any case, if there is effectively no limit (Vbus comes from the wall), then yes a regulator is probably an overkill. So make the case with no Vbus regulator (or regulator with no limit set) in DT be the max current. However, if the controller has a signal to turn on/off Vbus, then that should be modeled as a regulator. Rob -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
