linux-kernel - Re: [RFC v2 09/13] power: pwrseq: Add support for USB hubs with external power

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Date:	Thu, 5 May 2016 15:52:11 -0400
From:	Javier Martinez Canillas <javier@....samsung.com>
To:	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	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>
Cc:	tjakobi@...h.uni-bielefeld.de, m.szyprowski@...sung.com,
	hverkuil@...all.nl,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [RFC v2 09/13] power: pwrseq: Add support for USB hubs with
 external power

Hello Krzysztof,

On 05/05/2016 08:34 AM, Krzysztof Kozlowski wrote:
> Some USB devices on embedded boards have external power supply which has
> to be reset in certain conditions. Add pwrseq interface for this.
> 
> Signed-off-by: Krzysztof Kozlowski <k.kozlowski@...sung.com>
> ---
>  drivers/power/pwrseq/pwrseq.c | 44 +++++++++++++++++++++++++++++++++++++++++++
>  include/linux/pwrseq.h        |  8 ++++++++
>  2 files changed, 52 insertions(+)
> 
> diff --git a/drivers/power/pwrseq/pwrseq.c b/drivers/power/pwrseq/pwrseq.c
> index 495a19d3c30b..306265f55a10 100644
> --- a/drivers/power/pwrseq/pwrseq.c
> +++ b/drivers/power/pwrseq/pwrseq.c
> @@ -52,6 +52,43 @@ int mmc_pwrseq_alloc(struct mmc_host *host)
>  }
>  EXPORT_SYMBOL_GPL(mmc_pwrseq_alloc);
>  
> +struct pwrseq *pwrseq_alloc(struct device *dev)
> +{

This function is USB specific so better to call it usb_pwrseq_alloc() instead.

Although, this function has a lot of duplicated code from mmc_pwrseq_alloc()
so I think is better to keep the name generic and factorize the common code.

I expect other devices are also needing some kind of power seq in the future
so having a single alloc function instead of each for device type makes sense.

> +	struct device_node *np;
> +	struct pwrseq *p, *ret = NULL;
> +
> +	np = of_parse_phandle(dev->of_node, "usb-pwrseq", 0);

I know this is just an RFC but you should really add DT bindings for this.

Best regards,
-- 
Javier Martinez Canillas
Open Source Group
Samsung Research America