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

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Message-ID: <535A74DF.6090106@free-electrons.com>
Date:	Fri, 25 Apr 2014 16:44:47 +0200
From:	Gregory CLEMENT <gregory.clement@...e-electrons.com>
To:	Thomas Petazzoni <thomas.petazzoni@...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

On 25/04/2014 16:15, Thomas Petazzoni wrote:
> 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;

As explained in the comment: Not all platforms have a clk so it is not an
error if the clock does not exists.

> 
> 	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
> 


-- 
Gregory Clement, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com
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