On Tue, Jun 13, 2017 at 8:12 PM, Mathias Nyman <mathias.nyman@xxxxxxxxxxxxxxx> wrote: > On 06.06.2017 09:33, Thang Q. Nguyen wrote: >> >> On Mon, Jun 5, 2017 at 9:33 PM, Mathias Nyman <mathias.nyman@xxxxxxxxx> >> wrote: >>> >>> On 05.06.2017 15:57, Thang Q. Nguyen wrote: >>>> >>>> >>>> On Mon, Jun 5, 2017 at 6:14 PM, Mathias Nyman >>>> <mathias.nyman@xxxxxxxxxxxxxxx> wrote: >>>>> >>>>> >>>>> On 20.05.2017 10:24, Thang Q. Nguyen wrote: >>>>>> >>>>>> >>>>>> >>>>>> XHCI specification 1.1 does not require xHCI 1.0 compliant controllers >>>>>> to always enable hardware USB2 LPM. >>>>>> However, the current xHCI driver always enable it by setting HLE=1 >>>>>> when >>>>>> seeing HLC=1. This makes certain xHCI controllers that have broken >>>>>> USB2 >>>>>> HW LPM fail to work as there is no way to disable this feature. >>>>>> This patch adds support to control disabling USB2 Hardware LPM via >>>>>> DT/ACPI attribute. >>>>>> >>>>> >>>>> Wouldn't it be better to just keep xhci->hw_lpm_support = 0 if the >>>>> host >>>>> doesn't support Hardware LPM Capability, (HLC)? >>>>> >>>>> This should prevent all those extra steps getting here just to do >>>>> nothing. >>>> >>>> >>>> No, HLC = 0 means the host doesn't support Hardware LPM. >>>> The problem here is the host support Hardware LPM but there is a bug >>>> in host controller that make the LPM fail to work. >>>> >>> >>> So the host support hw LPM, and has its HLC capability bit set, >>> but in the end it just doesn't work at all, and should be prevented. >>> >>>> When debugging the host controller, we detect there are some holes in >>>> the current usb specifications which can can result in inter-operating >>>> problems between USB Host Controller and USB PHY. To be more specific, >>>> the specs have not clarified the resume recovery timing after the port >>>> has just waken up from L1. This can lead to different interpretations >>>> of the specs by Host Controller and PHY. What happened in our case is >>>> that a Host controller cannot work with a PHY right after resuming >>>> from L1 because these two Vendors have different views of the specs >>>> regarding LPM timing after L1. These views are contradictory and >>>> cannot work together. >>>> >>>> If Host Controller and PHY are from the same vendor, they might have >>>> some "internal handshake mechanisms" to avoid these holes of the USB >>>> specs. However, these mechanisms are not standardized in USB specs; >>>> and not all vendors follow these mechanisms. In fact, we have observed >>>> this kind of "internal handshake mechanism" in HOST Controller and PHY >>>> from SYNOPSYS DWC. So, we can say that if users use Host Controller >>>> and PHY from different Vendors, the inteopering problems after waking >>>> up from L1 are more likely to occur. >>> >>> >>> >>> Can you explain the reason why you prefer preventing hw lpm inside the >>> xhci_set_usb2_hardware_lpm() function instead of preventing hw lpm usage >>> all together for this platform -i.e. by not setting xhci->hw_lpm_support >> >> The reason I don't change in the xhci_add_in_port() function inside >> xhci-mem.c is because of the description for xhci->hw_lpm_support in >> the drivers/usb/host/xhci.h header file: support xHCI 1.0 spec USB2 >> hardware LPM. Per my understanding, this attribute is used to indicate >> if the host supports HW LPM and this can be checked via HLC. >> My intension is to support an option for user to disable the HW LPM >> because of some reasons (in my case because HW LPM is broken). > > > I think we should keep supporting new options separate from workarounds > for broken HW. So, I will continue to use usb2-lpm-disable to let kernel know that we want to disable USB2 HW LPM. > >>> >>> >>> Again, something like: >>> if (temp & XHCI_HLC && !(xhci->quirks & XHCI_HW_LPM_BROKEN)) >>> xhci->hw_lpm_support = 1; >> >> This should work too. But the DT/ACPI attribute should change to >> "usb2-lpm-broken". > > > This would be more clear for future developers and prevent them from > enabling hw lpm for this host to gain some powersaving. > > A new feature allowing optional host hw lpm disabling can then be written > separately, > preferable without using the quirk bits. How's about adding a new attribute such as sw_lpm_disable to the xhci_hcd struct to indicate that we will disable USB2 HW LPM by software? > > -Mathias -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
