linux-kernel - Re: [RFC v2 10/13] usb: hub: Power sequence the ports on activation

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Date:	Thu, 5 May 2016 10:09:47 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
cc:	devicetree@...r.kernel.org, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-samsung-soc@...r.kernel.org>, <linux-mmc@...r.kernel.org>,
	<linux-pm@...r.kernel.org>, <linux-usb@...r.kernel.org>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Sebastian Reichel <sre@...nel.org>,
	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Mark Brown <broonie@...nel.org>,
	<tjakobi@...h.uni-bielefeld.de>, <m.szyprowski@...sung.com>,
	<hverkuil@...all.nl>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [RFC v2 10/13] usb: hub: Power sequence the ports on activation

On Thu, 5 May 2016, Krzysztof Kozlowski wrote:

> The autodetection of attached USB device might not work on certain
> boards where the power is delivered externally. These devices also might
> require a hard reset. Use pwrseq for that in USB hub.
> 
> Signed-off-by: Krzysztof Kozlowski <k.kozlowski@...sung.com>
> ---
>  drivers/usb/core/hub.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> index 1c82fcc448f5..0fddaacc62bf 100644
> --- a/drivers/usb/core/hub.c
> +++ b/drivers/usb/core/hub.c
> @@ -26,6 +26,7 @@
>  #include <linux/mutex.h>
>  #include <linux/random.h>
>  #include <linux/pm_qos.h>
> +#include <linux/pwrseq.h>
>  
>  #include <asm/uaccess.h>
>  #include <asm/byteorder.h>
> @@ -1661,7 +1662,17 @@ static int hub_configure(struct usb_hub *hub,
>  
>  	usb_hub_adjust_deviceremovable(hdev, hub->descriptor);
>  
> +	/* FIXME: When do the pre-power-on? */

It's hard to answer this without knowing what pre-power-on involves.

Why not create a pwrseq_power_on() routine that does pre_power_on 
followed by post_power_on?

> +	/*
> +	for (i = 0; i < maxchild; i++)
> +		pwrseq_pre_power_on(hub->ports[i]->pwrseq);
> +	*/
> +
> +	for (i = 0; i < maxchild; i++)
> +		pwrseq_post_power_on(hub->ports[i]->pwrseq);

This is patch 10/13.  hub->ports[i]->pwrseq doesn't get added until 
11/13.  Obviously you never tried compiling each patch in the series.

> +
>  	hub_activate(hub, HUB_INIT);
> +

Unnecessary blank line added.

>  	return 0;
>  
>  fail:

Alan Stern