linux-kernel - Re: [PATCH v2 02/18] usb: host: xhci-plat: Add clocks support

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Message-ID: <20140425161517.20821c65@skate>
Date:	Fri, 25 Apr 2014 16:15:17 +0200
From:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
To:	Gregory CLEMENT <gregory.clement@...e-electrons.com>
Cc:	Mathias Nyman <mathias.nyman@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Felipe Balbi <balbi@...com>, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org, Jason Cooper <jason@...edaemon.net>,
	Andrew Lunn <andrew@...n.ch>,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
	Lior Amsalem <alior@...vell.com>,
	Tawfik Bayouk <tawfik@...vell.com>, devicetree@...r.kernel.org,
	Nadav Haklai <nadavh@...vell.com>,
	Rob Herring <robh+dt@...nel.org>,
	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>,
	Grant Likely <grant.likely@...aro.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 02/18] usb: host: xhci-plat: Add clocks support

Dear Gregory CLEMENT,

On Fri, 25 Apr 2014 16:07:00 +0200, Gregory CLEMENT wrote:
> Some platform (such as the Armada 38x ones) can gate the clock of
> their USB controller. This patch add the support for the clock, by
> enabling them during probe and disabling them on remove.
> 
> As not all platforms have clock support then enabling and disabling
> the clocks have been placed in separate functions. Then if the clocks
> are not supported we still can use the same calls, and there is no
> 
> Signed-off-by: Gregory CLEMENT <gregory.clement@...e-electrons.com>
> ---
>  drivers/usb/host/xhci-plat.c | 52 ++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 50 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/host/xhci-plat.c b/drivers/usb/host/xhci-plat.c
> index f5351af4b2c5..bb5d563f729c 100644
> --- a/drivers/usb/host/xhci-plat.c
> +++ b/drivers/usb/host/xhci-plat.c
> @@ -11,6 +11,7 @@
>   * version 2 as published by the Free Software Foundation.
>   */
>  
> +#include <linux/clk.h>
>  #include <linux/dma-mapping.h>
>  #include <linux/module.h>
>  #include <linux/of.h>
> @@ -85,6 +86,42 @@ static const struct hc_driver xhci_plat_xhci_driver = {
>  	.bus_resume =		xhci_bus_resume,
>  };
>  
> +#if defined(CONFIG_HAVE_CLK)
> +static int try_enable_clk(struct platform_device *pdev)
> +{
> +	struct clk *clk = devm_clk_get(&pdev->dev, NULL);
> +
> +	/* Not all platforms have a clk so it is not an error if the clock
> +	   does not exists. */
> +	if (!IS_ERR(clk))

Instead, do:

	if (IS_ERR(clk))
		return 0;

	return clk_prepare_enable(clk);

> +		if (clk_prepare_enable(clk))
> +			return  -ENODEV;
> +	return 0;
> +}
> +
> +static int try_disable_clk(struct platform_device *pdev)
> +{
> +	struct clk *clk = devm_clk_get(&pdev->dev, NULL);

No, this isn't correct: you shouldn't be getting the clock to
disable/unprepare it, otherwise you have an unbalanced number of
get()/put() calls on the clocks.

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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