linux-kernel - RE: [PATCH] usb: ohci-at91: Suspend the ports while USB suspending

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Message-ID: <B256D81BAE5131468A838E5D7A243641018CCD040F@penmbx01>
Date:	Thu, 4 Aug 2016 03:39:53 +0000
From:	"Yang, Wenyou" <Wenyou.Yang@...el.com>
To:	Alan Stern <stern@...land.harvard.edu>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Ferre, Nicolas" <Nicolas.FERRE@...el.com>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: RE: [PATCH] usb: ohci-at91: Suspend the ports while USB suspending

Hi Alan,
________________________________________
From: Alan Stern [stern@...land.harvard.edu]
Sent: Friday, May 13, 2016 2:11
To: Yang, Wenyou
Cc: Greg Kroah-Hartman; Ferre, Nicolas; linux-usb@...r.kernel.org; linux-kernel@...r.kernel.org; linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] usb: ohci-at91: Suspend the ports while USB suspending

On Thu, 12 May 2016, Wenyou Yang wrote:

> In order to get lower consumption, as a workaround, suspend
> the USB PORTA/B/C via set the SUSPEND_A/B/C bits of OHCI Interrupt
> Configuration Register while OHCI USB suspending.

What does this mean?  What does suspending a port do?  Is it the same
as a normal USB port suspend?

If it is the same, why doesn't the USB_PORT_FEAT_SUSPEND subcase of the
SetPortFeature case in ohci_hub_control() already take care of this?

Yes, you are right. 

We can use  the USB_PORT_FEAT_SUSPEND subcase of the
SetPortFeature case to take care this.

I will send a new patch, please help review it. Thanks a lot.

> This suspend operation must be done before stopping the USB clock,
> resume after the USB clock enabled.
>
> Signed-off-by: Wenyou Yang <wenyou.yang@...el.com>
> ---

> @@ -132,6 +135,17 @@ static void at91_stop_hc(struct platform_device *pdev)
>
>  /*-------------------------------------------------------------------------*/
>
> +struct regmap *at91_dt_syscon_sfr(void)
> +{
> +     struct regmap *regmap;
> +
> +     regmap = syscon_regmap_lookup_by_compatible("atmel,sama5d2-sfr");
> +     if (IS_ERR(regmap))
> +             return NULL;

If you get an error, the regmap pointer is set to NULL...

> @@ -197,6 +211,8 @@ static int usb_hcd_at91_probe(const struct hc_driver *driver,
>               goto err;
>       }
>
> +     ohci_at91->sfr_regmap = at91_dt_syscon_sfr();

With no other error checking...

> +
>       board = hcd->self.controller->platform_data;
>       ohci = hcd_to_ohci(hcd);
>       ohci->num_ports = board->ports;

> +static int ohci_at91_port_ctrl(struct regmap *regmap, bool enable)
> +{
> +     u32 regval;
> +     int ret;
> +
> +     if (IS_ERR(regmap))
> +             return PTR_ERR(regmap);
> +
> +     ret = regmap_read(regmap, SFR_OHCIICR, &regval);

And now what happens if regmap is NULL?  Hint: It won't be pretty...

Alan Stern


Best Regards,
Wenyou Yang