linux-kernel - Re: [PATCH v2 10/10] usb: chipidea: tegra: Add USB_TEGRA

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Date:   Sun, 5 Jan 2020 03:42:50 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Michał Mirosław <mirq-linux@...e.qmqm.pl>
Cc:     Peter Chen <peter.chen@....com>, Rob Herring <robh+dt@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Felipe Balbi <balbi@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 10/10] usb: chipidea: tegra: Add USB_TEGRA_PHY module
 to driver's dependencies

04.01.2020 14:01, Michał Mirosław пишет:
> On Sat, Jan 04, 2020 at 02:19:01AM +0300, Dmitry Osipenko wrote:
>> 03.01.2020 10:25, Michał Mirosław пишет:
>>> On Thu, Jan 02, 2020 at 06:17:47PM +0300, Dmitry Osipenko wrote:
>>>> 31.12.2019 00:02, Michał Mirosław пишет:
>>>>> On Tue, Dec 24, 2019 at 07:21:05AM +0300, Dmitry Osipenko wrote:
>>>>>> 24.12.2019 00:32, Michał Mirosław пишет:
>>>>>>> On Fri, Dec 20, 2019 at 07:31:08AM +0300, Dmitry Osipenko wrote:
>>>>>>>> 20.12.2019 06:56, Peter Chen пишет:
>>>>>>>>> On 19-12-20 04:52:38, Dmitry Osipenko wrote:
>>>>>>> [...]
>>>>>>>>>> --- a/drivers/usb/chipidea/ci_hdrc_tegra.c
>>>>>>>>>> +++ b/drivers/usb/chipidea/ci_hdrc_tegra.c
>>>>>>>>>> @@ -53,6 +53,12 @@ static int tegra_udc_probe(struct platform_device *pdev)
>>>>>>>>>>  	struct tegra_udc *udc;
>>>>>>>>>>  	int err;
>>>>>>>>>>  
>>>>>>>>>> +	if (IS_MODULE(CONFIG_USB_TEGRA_PHY)) {
>>>>>>>>>> +		err = request_module("phy_tegra_usb");
>>>>>>>>>> +		if (err)
>>>>>>>>>> +			return err;
>>>>>>>>>> +	}
>>>>>>>>>> +
>>>>>>>>>
>>>>>>>>> Why you do this dependency, if this controller driver can't
>>>>>>>>> get USB PHY, it should return error. What's the return value
>>>>>>>>> after calling below:
>>>>>>>>>
>>>>>>>>> 	udc->phy = devm_usb_get_phy_by_phandle(&pdev->dev, "nvidia,phy", 0);
>>>>>>>>
>>>>>>>> It returns -EPROBE_DEFER when phy_tegra_usb isn't loaded.
>>>>>>>
>>>>>>> How are other driver modules autoloaded? Isn't there an appropriate
>>>>>>> MODALIAS or MODULE_DEVICE_TABLE in there?
>>>>>>
>>>>>> Hello Michał,
>>>>>>
>>>>>> The phy_tegra_usb module is fine by itself, it's getting autoloaded.
>>>>>>
>>>>>> The problem is that ci_hdrc_tegra module depends on the phy_tegra_usb
>>>>>> module and thus the PHY module should be loaded before the CI module,
>>>>>> otherwise CI driver fails with the EPROBE_DEFER.
>>>>>
>>>>> Why, then, is CI driver not being probed again after PHY driver loads?
>>>>> EPROBE_DEFER is what should cause driver core to re-probe a device after
>>>>> other devices appear (PHY in this case).
>>>>
>>>> CI driver is getting re-probed just fine if PHY's driver module is
>>>> loaded manually after loading the CI's module. This patch removes this
>>>> necessity to manually load PHY's module.
>>>>
>>>> This is just a minor convenience change that brings the CI's driver
>>>> loading behaviour on par with the behaviour of loading Tegra's EHCI
>>>> driver module.
>>>
>>> I fully understand the goal, but what I'm missing is that why this
>>> doesn't work out of the box? If the PHY module is autoloaded, and so is
>>> CI driver, and (as I understand) the driver's probe() correctly returns
>>> EPROBE_DEFER when PHY is not probed yet, then I guess that means bug
>>> somewhere else and the patch just covers it up.
>>
>> It works out of the box, but it also could work a bit better in a case
>> of manually reloading modules. Perhaps it should be possible to derive
>> module dependencies from the Kconfig dependencies, apparently kernel
>> doesn't support it yet or maybe there is some reason why it can't be done.
> 
> Kconfig change I'm ok with as it simplifies kernel configuration.
> The request_module() is something I would advise against, because if I
> do manual module loading, I usually don't want modules loaded
> automatically.

Okay, I'll drop the request_module since it raises a bit too many
questions and since it's an optional change that won't be needed once
Tegra EHCI driver will be squashed into CI.