linux-kernel - Re: [PATCH v2 03/10] mfd: cros_ec: Instantiate sub-devices from device tree

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Message-ID: <555338F3.8030507@collabora.co.uk>
Date:	Wed, 13 May 2015 13:43:47 +0200
From:	Javier Martinez Canillas <javier.martinez@...labora.co.uk>
To:	Lee Jones <lee.jones@...aro.org>
CC:	Samuel Ortiz <sameo@...ux.intel.com>,
	Olof Johansson <olof@...om.net>,
	Doug Anderson <dianders@...omium.org>,
	Bill Richardson <wfrichar@...omium.org>,
	Simon Glass <sjg@...gle.com>,
	Gwendal Grignou <gwendal@...gle.com>,
	Stephen Barber <smbarber@...omium.org>,
	Filipe Brandenburger <filbranden@...gle.com>,
	Todd Broch <tbroch@...omium.org>,
	Alexandru M Stan <amstan@...omium.org>,
	Heiko Stuebner <heiko@...ech.de>,
	linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 03/10] mfd: cros_ec: Instantiate sub-devices from device
 tree

Hello Lee,

On 05/13/2015 01:32 PM, Lee Jones wrote:
> On Sat, 09 May 2015, Javier Martinez Canillas wrote:
> 
>> From: Todd Broch <tbroch@...omium.org>
>> 
>> If the EC device tree node has sub-nodes, try to instantiate them as
>> MFD sub-devices.  We can configure the EC features provided by the board.
>> 
>> Signed-off-by: Todd Broch <tbroch@...omium.org>
>> Signed-off-by: Javier Martinez Canillas <javier.martinez@...labora.co.uk>
>> Tested-by: Heiko Stuebner <heiko@...ech.de>
>> Reviewed-by: Gwendal Grignou <gwendal@...omium.org>
>> Tested-by: Gwendal Grignou <gwendal@...omium.org>
>> ---
>> 
>> Changes since v1:
>>   - Added Heiko Stuebner and Gwendal Grignou Tested-by tag
>>   - Added Gwendal Grignou Reviewed-by tag
>>   - Use automatic device ID instead of 1 as suggested by Lee Jones
>>   - Remove #ifdeffery and check for of_node to register sub-devices
>>     Suggested by Lee Jones
>> ---
>>  drivers/mfd/cros_ec.c | 22 +++++++++++-----------
>>  1 file changed, 11 insertions(+), 11 deletions(-)
>> 
>> diff --git a/drivers/mfd/cros_ec.c b/drivers/mfd/cros_ec.c
>> index c4aecc6f8373..1574a9352a6d 100644
>> --- a/drivers/mfd/cros_ec.c
>> +++ b/drivers/mfd/cros_ec.c
>> @@ -17,6 +17,7 @@
>>   * battery charging and regulator control, firmware update.
>>   */
>>  
>> +#include <linux/of_platform.h>
>>  #include <linux/interrupt.h>
>>  #include <linux/slab.h>
>>  #include <linux/module.h>
>> @@ -109,18 +110,8 @@ EXPORT_SYMBOL(cros_ec_cmd_xfer);
>>  
>>  static const struct mfd_cell cros_devs[] = {
>>  	{
>> -		.name = "cros-ec-keyb",
>> -		.id = 1,
>> -		.of_compatible = "google,cros-ec-keyb",
>> -	},
>> -	{
>> -		.name = "cros-ec-i2c-tunnel",
>> -		.id = 2,
>> -		.of_compatible = "google,cros-ec-i2c-tunnel",
>> -	},
>> -	{
>>  		.name = "cros-ec-ctl",
>> -		.id = 3,
>> +		.id = PLATFORM_DEVID_AUTO,
>>  	},
>>  };
>>  
>> @@ -150,6 +141,15 @@ int cros_ec_register(struct cros_ec_device *ec_dev)
>>  		return err;
>>  	}
>>  
>> +	if (IS_ENABLED(CONFIG_OF) && dev->of_node) {
> 
> You don't need to check for OF.  of_node will be NULL if OF isn't
> enabled.
>

Yes, you don't need it but IS_ENABLED(CONFIG_OF) causes the check to be
optimized away by the compiler if CONFIG_OF is not enabled AFAIK.

Without the IS_ENABLED(CONFIG_OF) check, this becomes a pointless pointer
check that will always evaluate to false on systems without CONFIG_OF
since as you said of_node will be present when CONFIG_OF is not enabled.
But the compiler has no way to know it will always be NULL to optimize it
away AFAICT.
 
>> +		err = of_platform_populate(dev->of_node, NULL, NULL, dev);
>> +		if (err) {
>> +			mfd_remove_devices(dev);
>> +			dev_err(dev, "Failed to register sub-devices\n");
>> +			return err;
>> +		}
>> +	}
>> +
>>  	dev_info(dev, "Chrome EC device registered\n");
>>  
>>  	return 0;
> 

Best regards,
Javier
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