linux-kernel - Re: [PATCH 2/2] usb: chipidea: Wait 50 ms before reading ID bit

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Message-ID: <20150630021145.GB7586@shlinux2>
Date:	Tue, 30 Jun 2015 10:11:46 +0800
From:	Peter Chen <peter.chen@...escale.com>
To:	Mike Looijmans <mike.looijmans@...ic.nl>
CC:	<lars@...afoo.de>, <linux-usb@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] usb: chipidea: Wait 50 ms before reading ID bit

On Fri, Jun 26, 2015 at 03:47:04PM +0200, Mike Looijmans wrote:
> The datasheet for the USB343x PHY mentions a 50ms wait time before
> reading back the ID bit after enabling the internal pull-up or a
> reset:
> "To monitor the status of the ID pin, the Link activates the IdPullup
> bit in the OTG Control register, waits 50mS and then reads the status
> of the IdGnd bit in the USB Interrupt Status register."
> Implement this by adding a 50ms sleep at the only point in the code
> where the ID status is being read without IRQ trigger.

This 50mS delay is dedicated for this PHY, you may add it at the
PHY driver.

> 
> When starting the board with a USB cable connected to a PC, the
> system would activate host mode, then in ~20ms get an ID IRQ and
> attempt to switch to gadget mode. This then failed because the
> VBUS will not drop to zero (because the host is supplying it).
> 
> After this patch, the system starts up correctly and selects
> gadget mode immediately, and the USB link works. It also fixes
> the issue that the VBUS supply was being activated while already
> being supplied from the host PC.
> 
> Signed-off-by: Mike Looijmans <mike.looijmans@...ic.nl>
> ---
>  drivers/usb/chipidea/core.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/usb/chipidea/core.c b/drivers/usb/chipidea/core.c
> index c865abe..4c6cf48 100644
> --- a/drivers/usb/chipidea/core.c
> +++ b/drivers/usb/chipidea/core.c
> @@ -801,6 +801,7 @@ static int ci_hdrc_probe(struct platform_device *pdev)
>  
>  	if (ci->roles[CI_ROLE_HOST] && ci->roles[CI_ROLE_GADGET]) {
>  		if (ci->is_otg) {
> +			msleep(50); /* Datasheet: Wait 50ms to read ID */
>  			ci->role = ci_otg_role(ci);
>  			/* Enable ID change irq */
>  			hw_write_otgsc(ci, OTGSC_IDIE, OTGSC_IDIE);
> -- 
> 1.9.1
> 

-- 

Best Regards,
Peter Chen
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