linux-kernel - Re: [PATCH v5 1/2] usb: host: plat: Enable xhci plat runtime PM

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Date:   Mon, 6 Feb 2017 13:26:14 +0800
From:   Baolin Wang <baolin.wang@...aro.org>
To:     Mathias Nyman <mathias.nyman@...ux.intel.com>
Cc:     Mathias Nyman <mathias.nyman@...el.com>,
        Felipe Balbi <balbi@...nel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Mark Brown <broonie@...nel.org>,
        USB <linux-usb@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Alan Stern <stern@...land.harvard.edu>
Subject: Re: [PATCH v5 1/2] usb: host: plat: Enable xhci plat runtime PM

Hi Mathias,

On 31 January 2017 at 21:14, Mathias Nyman
<mathias.nyman@...ux.intel.com> wrote:
> On 16.01.2017 12:56, Baolin Wang wrote:
>>
>> Hi Mathias,
>
>
> Hi
>
> Sorry about the long review delay
> CC Alan in case my pm assumptions need to be corrected
>
>
>>
>> On 13 December 2016 at 15:49, Baolin Wang <baolin.wang@...aro.org> wrote:
>>>
>>> Enable the xhci plat runtime PM for parent device to suspend/resume xhci.
>>> Also call pm_runtime_get_noresume() in probe() function in case the
>>> parent
>>> device doesn't call suspend/resume callback by runtime PM now.
>>>
>>> Signed-off-by: Baolin Wang <baolin.wang@...aro.org>
>>> ---
>>> Changes since v4:
>>>   - No updates.
>>>
>>> Changes since v3:
>>>   - Fix kbuild error.
>>>
>>> Changes since v2:
>>>   - Add pm_runtime_get_noresume() in probe() function.
>>>   - Add pm_runtime_set_suspended()/pm_runtime_put_noidle() in remove()
>>> function.
>>>
>>> Changes since v1:
>>>   - No updates.
>>> ---
>>
>>
>> Do you have any comments about this patch? Thanks.
>>
>>>   drivers/usb/host/xhci-plat.c |   41
>>> ++++++++++++++++++++++++++++++++++++-----
>>>   1 file changed, 36 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/drivers/usb/host/xhci-plat.c b/drivers/usb/host/xhci-plat.c
>>> index ed56bf9..5805c6a 100644
>>> --- a/drivers/usb/host/xhci-plat.c
>>> +++ b/drivers/usb/host/xhci-plat.c
>>> @@ -246,6 +246,10 @@ static int xhci_plat_probe(struct platform_device
>>> *pdev)
>>>          if (ret)
>>>                  goto dealloc_usb2_hcd;
>>>
>>> +       pm_runtime_get_noresume(&pdev->dev);
>>> +       pm_runtime_set_active(&pdev->dev);
>>> +       pm_runtime_enable(&pdev->dev);
>>> +
>>>          return 0;
>>>
>>>
>
> To me this looks like we are not really enabling runtime pm for xhci, we
> increment the
> usage count in probe, and keep it until remove is called.
>
> This would normally prevent parent dwc3 from runtime suspending, but I see
> that in patch 2/2 adds
> pm_suspend_ignore_children(dev, true) to dwc3, and, that dwc3 actually
> controls xhci runtime
> pm by calling pm_runtime_get/put for xhci in its own dwc3
> runtime_suspend/resume callbacks.
>
> Looks a bit upside down to me, what's the reason for this?
>
> what prevents calling pm_runtime_put_* before leaving probe in xhci and let
> pm code handle
> the runtime suspend and parent/child relationships?

When dwc3 controller is working on host mode, which will create and
add the USB hcd for host side. Then if we want to suspend dwc3
controller as host mode, the USB device (bus) of host side will
runtime suspend automatically if there are no slave attached (by
usb_runtime_suspend()--->usb_suspend_both()--->usb_suspend_interface()--->usb_suspend_device()--->generic_suspend()--->hcd_bus_suspend()--->xhci_bus_suspend()),
but we should not suspend xHCI device (issuing xhci_suspend()) now,
since some other  controllers did not implement the runtime PM to
control xHCI device's runtime state, which will cause other
controllers can not resume xHCI device (issuing xhci_resume()) if the
xHCI device suspend automatically by its child device. Thus we should
get the runtime count for xHCI device in xhci_plat_probe() in case
xHCI device will also suspend automatically by its child device.
According to that, for xHCI device's parent: dwc3 device, we should
put the xHCI device's runtime count to suspend xHCI device manually.

-- 
Baolin.wang
Best Regards