linux-kernel - Re: [PATCH v1 5/8] usb: chipidea: tegra: Support host mode

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Date:   Wed, 16 Dec 2020 12:53:38 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Peter Chen <peter.chen@....com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Felipe Balbi <balbi@...nel.org>,
        Matt Merhar <mattmerhar@...tonmail.com>,
        Nicolas Chauvet <kwizart@...il.com>,
        Peter Geis <pgwipeout@...il.com>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 5/8] usb: chipidea: tegra: Support host mode

16.12.2020 12:32, Peter Chen пишет:
>  
>>>>
>>>>  struct tegra_usb_soc_info {
>>>>  	unsigned long flags;
>>>> +	unsigned int txfifothresh;
>>>> +	enum usb_dr_mode dr_mode;
>>>> +};
>>>> +
>>>> +static const struct tegra_usb_soc_info tegra20_ehci_soc_info = {
>>>> +	.flags = CI_HDRC_REQUIRES_ALIGNED_DMA |
>>>> +		 CI_HDRC_OVERRIDE_PHY_CONTROL,
>>>> +	.dr_mode = USB_DR_MODE_HOST,
>>>> +	.txfifothresh = 10,
>>>> +};
>>>> +
>>>> +static const struct tegra_usb_soc_info tegra30_ehci_soc_info = {
>>>> +	.flags = CI_HDRC_REQUIRES_ALIGNED_DMA |
>>>> +		 CI_HDRC_OVERRIDE_PHY_CONTROL
>>>> +	.dr_mode = USB_DR_MODE_HOST,
>>>> +	.txfifothresh = 16,
>>>>  };
>>>>
>>>>  static const struct tegra_usb_soc_info tegra_udc_soc_info = {
>>>> -	.flags = CI_HDRC_REQUIRES_ALIGNED_DMA,
>>>> +	.flags = CI_HDRC_REQUIRES_ALIGNED_DMA |
>>>> +		 CI_HDRC_OVERRIDE_PHY_CONTROL,
>>>> +	.dr_mode = USB_DR_MODE_UNKNOWN,
>>>>  };
>>>
>>> What's the usage for this dr_mode? Does these three SoCs only supports
>>> single mode, it usually sets dr_mode at board dts file to indicate USB
>>> role for this board.
>>
>> All Tegra SoCs have three USB controllers.  Only one of these three controllers
>> supports peripheral / OTG modes, the other two controllers are fixed to the
>> host mode and device trees do not specify the dr_mode for the host
>> controllers.
>>
>> Hence we need to enforce the dr_mode=host for the host-mode controllers.
>>
>> For UDC the default mode is "unknown" because actual mode comes from a
>> board's device tree.
>>
> 
> You could add dr_mode property at usb node of soc.dtsi to fulfill that.

This will break older DTBs, we can't do this.

...
>>>>  static int ehci_ci_portpower(struct usb_hcd *hcd, int portnum, bool
>>>> enable)  {
>>>>  	struct ehci_hcd *ehci = hcd_to_ehci(hcd); @@ -160,14 +166,14 @@
>>>> static int host_start(struct ci_hdrc *ci)
>>>>  		pinctrl_select_state(ci->platdata->pctl,
>>>>  				     ci->platdata->pins_host);
>>>>
>>>> +	ci->hcd = hcd;
>>>> +
>>>>  	ret = usb_add_hcd(hcd, 0, 0);
>>>>  	if (ret) {
>>>>  		goto disable_reg;
>>>>  	} else {
>>>>  		struct usb_otg *otg = &ci->otg;
>>>>
>>>> -		ci->hcd = hcd;
>>>> -
>>>
>>> Why this changed?
>>
>> The ci->hcd is used by tegra_usb_notify_event() to handle reset event and the
>> reset happens once usb_add_hcd() is invoked.  Hence we need to pre-assign
>> the hcd pointer, otherwise there will be a NULL dereference.
> 
> Get it, please set ci->hcd as NULL at error path.

Ok, thanks.