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

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Date:	Thu, 12 May 2016 14:11:14 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Wenyou Yang <wenyou.yang@...el.com>
cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	<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?

> 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