linux-kernel - Re: [PATCH v3 1/2] power: supply: ltc2941-battery-gauge: Add OF device ID table

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Date:   Wed, 15 Mar 2017 18:25:26 -0300
From:   Javier Martinez Canillas <javier@....samsung.com>
To:     Sebastian Reichel <sre@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Mike Looijmans <mike.looijmans@...ic.nl>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH v3 1/2] power: supply: ltc2941-battery-gauge: Add OF
 device ID table

Hello Sebastian,

On 03/15/2017 06:10 PM, Sebastian Reichel wrote:
> Hi Javier,
> 
> On Wed, Mar 15, 2017 at 05:59:24PM -0300, Javier Martinez Canillas wrote:
>> Hello Sebastian,
>>
>> On 03/15/2017 05:55 PM, Sebastian Reichel wrote:
>>> Hi,
>>>
>>> On Wed, Mar 15, 2017 at 12:43:48AM -0300, Javier Martinez Canillas wrote:
>>>> The driver doesn't have a struct of_device_id table but supported devices
>>>> are registered via Device Trees. This is working on the assumption that a
>>>> I2C device registered via OF will always match a legacy I2C device ID and
>>>> that the MODALIAS reported will always be of the form i2c:<device>.
>>>
>>> I don't get hits for "grep -r ltc294[13]" in arch/.
>>>
>>
>> There isn't a mainline DTS that use these but the compatible strings (without a
>> vendor prefix) are listed in the following DT binding document:
>>
>> Documentation/devicetree/bindings/power/supply/ltc2941.txt.
> 
> Looks like I didn't notice when I merged the binding document :(
>

No worries, is not the only DT binding doc for an I2C device that does this.
One disadvantage of the I2C core allowing to match I2C devices using the I2C
device ID table as fallback and always reporting an i2c:<foo> modalias is that
people stop caring about vendor prefixes and this implementation detail leaks
into the DTS and DT binding docs.
 
>>>> But this could change in the future so the correct approach is to have an
>>>> OF device ID table if the devices are registered via OF.
>>>>
>>>> The compatible strings don't have a vendor prefix because that's how it's
>>>> used currently, and changing this will be a Device Tree ABI break.
>>>
>>> I think the DT strings should have a vendor prefix.
>>> So I will only queue this with an explicit Acked-By from Rob or Mark.
>>>
>>
>> Yes, I agree with you. I don't know though what should happen with DT bindings
>> that mentions a compatible without a vendor prefix as the one for this driver.
> 
> Adding Rob, Mark (DT binding maintainers) and Mike (submitter of
> the DT binding). I think we should add vendor prefix. If it is
> actually used we could keep the variant without the vendor prefix
> with a deprecation notice in the DT binding document.
>

Sounds good to me.

> -- Sebastian
> 
>>> -- Sebastian
>>>
>>>> Changes in v3:
>>>> - Don't use of_match_ptr() to avoid build warning when CONFIG_OF is disabled.
>>>>
>>>> Changes in v2:
>>>>  Fix build warning reported by kbuild test robot.
>>>> - Fix wrong compatible strings due a copy & paste error.
>>>>
>>>>  drivers/power/supply/ltc2941-battery-gauge.c | 19 +++++++++++++++++--
>>>>  1 file changed, 17 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/power/supply/ltc2941-battery-gauge.c b/drivers/power/supply/ltc2941-battery-gauge.c
>>>> index 4adf2ba021ce..d3052be1bead 100644
>>>> --- a/drivers/power/supply/ltc2941-battery-gauge.c
>>>> +++ b/drivers/power/supply/ltc2941-battery-gauge.c
>>>> @@ -9,6 +9,7 @@
>>>>   */
>>>>  #include <linux/kernel.h>
>>>>  #include <linux/module.h>
>>>> +#include <linux/of_device.h>
>>>>  #include <linux/types.h>
>>>>  #include <linux/errno.h>
>>>>  #include <linux/swab.h>
>>>> @@ -61,7 +62,7 @@ struct ltc294x_info {
>>>>  	struct power_supply *supply;	/* Supply pointer */
>>>>  	struct power_supply_desc supply_desc;	/* Supply description */
>>>>  	struct delayed_work work;	/* Work scheduler */
>>>> -	int num_regs;	/* Number of registers (chip type) */
>>>> +	unsigned long num_regs;	/* Number of registers (chip type) */
>>>>  	int charge;	/* Last charge register content */
>>>>  	int r_sense;	/* mOhm */
>>>>  	int Qlsb;	/* nAh */
>>>> @@ -387,7 +388,7 @@ static int ltc294x_i2c_probe(struct i2c_client *client,
>>>>  
>>>>  	np = of_node_get(client->dev.of_node);
>>>>  
>>>> -	info->num_regs = id->driver_data;
>>>> +	info->num_regs = (unsigned long)of_device_get_match_data(&client->dev);
>>>>  	info->supply_desc.name = np->name;
>>>>  
>>>>  	/* r_sense can be negative, when sense+ is connected to the battery
>>>> @@ -497,9 +498,23 @@ static const struct i2c_device_id ltc294x_i2c_id[] = {
>>>>  };
>>>>  MODULE_DEVICE_TABLE(i2c, ltc294x_i2c_id);
>>>>  
>>>> +static const struct of_device_id ltc294x_i2c_of_match[] = {
>>>> +	{
>>>> +		.compatible = "ltc2941",
>>>> +		.data = (void *)LTC2941_NUM_REGS
>>>> +	},
>>>> +	{
>>>> +		.compatible = "ltc2943",
>>>> +		.data = (void *)LTC2943_NUM_REGS
>>>> +	},
>>>> +	{ },
>>>> +};
>>>> +MODULE_DEVICE_TABLE(of, ltc294x_i2c_of_match);
>>>> +
>>>>  static struct i2c_driver ltc294x_driver = {
>>>>  	.driver = {
>>>>  		.name	= "LTC2941",
>>>> +		.of_match_table = ltc294x_i2c_of_match,
>>>>  		.pm	= LTC294X_PM_OPS,
>>>>  	},
>>>>  	.probe		= ltc294x_i2c_probe,
>>>> -- 
>>>> 2.9.3
>>>>
>>
>> Best regards,
>> -- 
>> Javier Martinez Canillas
>> Open Source Group
>> Samsung Research America

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