On Mon, Aug 29 2016, Baolin Wang wrote: > Hi Felipe, > > On 11 August 2016 at 11:14, Baolin Wang <baolin.wang@xxxxxxxxxx> wrote: >> Hi Felipe, >> >> On 1 August 2016 at 15:09, Baolin Wang <baolin.wang@xxxxxxxxxx> wrote: >>> Currently the Linux kernel does not provide any standard integration of this >>> feature that integrates the USB subsystem with the system power regulation >>> provided by PMICs meaning that either vendors must add this in their kernels >>> or USB gadget devices based on Linux (such as mobile phones) may not behave >>> as they should. Thus provide a standard framework for doing this in kernel. >>> >>> Now introduce one user with wm831x_power to support and test the usb charger, >>> which is pending testing. Moreover there may be other potential users will use >>> it in future. >> >> Could you please apply this patchset into your 'next' branch if you >> have no comments about it? Thank you. > > Since there are no other comments about this patchset for a long time, > could you please apply this patchset? Thanks. Sorry, I should have replied earlier. Tim Bird mentioned on the ksummit-discuss list that there was a frustration with this not making progress so I decided to contribute what I could now. I think this patch set is attempting to address an important problem that needs solving. However I think it gets some key aspects wrong. Maybe they can get fixed up after the patchset is upstream, maybe they should be fixed first - I have no strong opinion on that. My main complaints involve the detection and handling of the different charger types - DCP, CDP, ACA etc. The big-picture requirement here that the PHY will detect the physical properties of the cable (e.g. resistance to ground on ID) and determine the type of charger expected. This information must be communicated to the PMIC "power_supply" device so it can regulate the power being drawn through the cable. The first problem is that there are two different ways that the distinction between DCP, CDP, ACA etc can be represented in Linux. They are cable types in the 'extcon' subsystem, and they are power_supply types in the 'power_supply' subsystem. This duplication is confusing. It is not caused by your patch set, but I believe your patchset needs to work with the duplication and I think it does so poorly. In my mind, the power_supply should *not* know about this distinction at all (except possibly as an advisor attribute simiarly to the current battery technology attribute). The other types it knows of are "AC", "USB", and "BATTERY". The contrast between these is quite different From the contrast between DCP, CDP, ACA, which, from the perspective of the power supply, are almost irrelevant. Your patchset effectively examines the power_supply_type of one power_supply, and communicates it to another. It isn't clear to me how the first power_supply gets the information, or what the relationship between the two power_supplies is meant to be. It makes much more sense, to me, to utilized the knowledge of this distinction that extcon provides. A usb PHY can register an extcon, declare the sorts of cables that it can detect, and tell the extcon as cables appear or disappear. The PMIC power_supply can then register with that extcon for events and can find out when a cable is attached, and what sort of cable. Your usb-charging framework would be well placed to help the power_supply to find the correct extcon, and possibly even to handle the registration for events. Your framework does currently register with extcon, but only listens for EXTCON_USB cables. I don't think that cable type is (reliably) reported when a DCP (for example) is plugged in. Here there is another problem that is not of your making, but still needs fixing. Extcon declares a number of cable types like: /* USB external connector */ #define EXTCON_USB 1 #define EXTCON_USB_HOST 2 /* Charging external connector */ #define EXTCON_CHG_USB_SDP 5 /* Standard Downstream Port */ #define EXTCON_CHG_USB_DCP 6 /* Dedicated Charging Port */ #define EXTCON_CHG_USB_CDP 7 /* Charging Downstream Port */ #define EXTCON_CHG_USB_ACA 8 /* Accessory Charger Adapter */ #define EXTCON_CHG_USB_FAST 9 #define EXTCON_CHG_USB_SLOW 10 However it doesn't define what those mean, so we are left to guess. They each correspond to bits in a bitmap, so a cable can have multiple types. I think the best interpretation is that: EXTCON_USB means that the cable carries USB data from a host. EXTCON_USB_HOST means that that cable carries USB data to a host. EXTCON_CHG_* means that power is available as described in the standards. (what EXTCON_CHG_USB_FAST and EXTCON_CHG_USB_SLOW mean is not at all clear). There is some support for this in the code, but it is not universally acknowledged. For a USB charging framework to be genuinely useful, it must (I think) make sure this issue gets clarified, and the various cable types used properly. Once the cable/charger type has been determined, the PMIC power_supply needs to use this information. Your current patches make use of this information in ways that are wrong in two respects. Firstly, you have made the current limit associated with each cable type configurable (__usb_charger_set_cur_limit_by_type). This is nonsense. The standard (e.g. BC-1.2) declares what the current limits are. There is no reason for those not to be hard coded. Secondly, you treat each charger type as having a single "cur_limit" and utilize that limit by telling the PMIC to draw that much current. Again, this is inconsistent with the specification. BC-1.2 defines, for each charger type, a minimum and maximum current level. The minimum should always be available. Attempting to draw more than that (but less that the max) might work or might cause the charger to shut down, but you can be sure that the charger will respond to the increased load by first reducing the voltage, and will not shut down until the voltage has dropped below 2V. If you try to draw more current than the maximum, then the charger might shut down before the voltage drops below 2V. Given this understanding of the current available from the charger, there are two approaches the PMIC might take. 1/ if the PMIC is able to exercise fine control over the current it draws, and if it can monitor the voltage on the charger, then it could gradually increase the power being requested until the voltage drops below some threshold (e.g. 4.75V), and then (probably) back off a little. It should only increase at most up to the maximum, even if the voltage remains high. It should probably start at zero rather than at the minimum. This allows for lossage elsewhere. 2/ If the PMIC cannot measure voltage, or doesn't have sufficiently fine control of the current requested, then it should request only the minimum available current. Any more is not safe. So your USB charging framework should communicate the MIN and MAX as specified in the standard, and allow the PMIC to use that information as appropriate. A library routine to support the incremental increase in current drain would probably be appreciated by PMIC driver writers. A more details discussion of this problem-space can be found at https://lwn.net/Articles/693027/ and an analysis of the functionality currently available in the kernel (which adds a number of specifics to the above) can be found at https://lwn.net/Articles/694062/ NeilBrown
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