linux-kernel - Re: [PATCH 2/3] usb: xhci: tegra: Add runtime PM support

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Date:   Fri, 9 Mar 2018 11:13:13 +0000
From:   Jon Hunter <jonathanh@...dia.com>
To:     Thierry Reding <thierry.reding@...il.com>
CC:     Mathias Nyman <mathias.nyman@...ux.intel.com>,
        Mathias Nyman <mathias.nyman@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        <linux-usb@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] usb: xhci: tegra: Add runtime PM support


On 09/03/18 08:36, Thierry Reding wrote:
> On Thu, Mar 08, 2018 at 09:31:07PM +0000, Jon Hunter wrote:
>>
>> On 01/03/18 14:18, Mathias Nyman wrote:
>>> On 14.02.2018 18:34, Jon Hunter wrote:
>>>> Add runtime PM support to the Tegra XHCI driver and move the function
>>>> calls to enable/disable the clocks, regulators and PHY into the runtime
>>>> PM callbacks.
>>>>
>>>> Signed-off-by: Jon Hunter <jonathanh@...dia.com>
>>>> ---
>>>>   drivers/usb/host/xhci-tegra.c | 80
>>>> ++++++++++++++++++++++++++++++-------------
>>>>   1 file changed, 56 insertions(+), 24 deletions(-)
>>>>
>>>> diff --git a/drivers/usb/host/xhci-tegra.c
>>>> b/drivers/usb/host/xhci-tegra.c
>>>> index 02b0b24faa58..42aa67858b53 100644
>>>> --- a/drivers/usb/host/xhci-tegra.c
>>>> +++ b/drivers/usb/host/xhci-tegra.c
>>>> @@ -18,6 +18,7 @@
>>>>   #include <linux/phy/tegra/xusb.h>
>>>>   #include <linux/platform_device.h>
>>>>   #include <linux/pm.h>
>>>> +#include <linux/pm_runtime.h>
>>>>   #include <linux/regulator/consumer.h>
>>>>   #include <linux/reset.h>
>>>>   #include <linux/slab.h>
>>>> @@ -1067,22 +1068,12 @@ static int tegra_xusb_probe(struct
>>>> platform_device *pdev)
>>>>        */
>>>>       platform_set_drvdata(pdev, tegra);
>>>>   -    err = tegra_xusb_clk_enable(tegra);
>>>> -    if (err) {
>>>> -        dev_err(&pdev->dev, "failed to enable clocks: %d\n", err);
>>>> -        goto put_usb2;
>>>> -    }
>>>> -
>>>> -    err = regulator_bulk_enable(tegra->soc->num_supplies,
>>>> tegra->supplies);
>>>> -    if (err) {
>>>> -        dev_err(&pdev->dev, "failed to enable regulators: %d\n", err);
>>>> -        goto disable_clk;
>>>> -    }
>>>> +    pm_runtime_enable(&pdev->dev);
>>>>   -    err = tegra_xusb_phy_enable(tegra);
>>>> +    err = pm_runtime_get_sync(&pdev->dev);
>>>>       if (err < 0) {
>>>
>>> Does this mean that if runtime PM is disabled then clocks and regulator
>>> will never be enabled
>>> for Tegra xhci?
>>>
>>> How about keeping the clock and regualtor enabling in probe, and instead
>>> add something like:
>>>
>>> pm_runtime_set_active(&pdev->dev);
>>> pm_runtime_enable(&pdev->dev);
>>> pm_runtime_get_noresume(&pdev->dev);
>>
>> For 64-bit Tegra there is a dependency on CONFIG_PM, but for 32-bit
>> AFAIK there is not and so yes we should handle the case when PM_RUNTIME
>> is disabled.
>>
>> Typically we do something like ...
>>
>>     pm_runtime_enable(&pdev->dev);
>>     if (!pm_runtime_enabled(&pdev->dev))
>> 	ret = tegra_xusb_runtime_resume(&pdev->dev);
>>     else
>>         ret = pm_runtime_get_sync(&pdev->dev);
>>
>> That way we can keep the regulator and clock stuff in the handler. I
>> will update this series.
> 
> Is there any good reason why we don't depend on PM for 32-bit as well?

Not that I am aware of.

> I'm not aware of any differences in drivers that are 32-bit specific for
> Tegra, and I'm not even sure the !PM case gets any testing at all. And
> even if, do we really still want to support that?
> 
> I don't see any advantage these days for having it disabled.

It would be fine IMO.

Cheers
Jon

-- 
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