Subject: Re: [PATCH net-next 2/2] net: netcp: select davinci_mdio driver by default

From: Murali Karicheri <[email-masked]>
Date: Mon, 2 Mar 2015 16:45:42 -0500

On 03/02/2015 11:11 AM, Tony Lindgren wrote:
> * Murali Karicheri<[email-masked]>  [150227 12:59]:
>> On 02/27/2015 11:29 AM, Tony Lindgren wrote:
>>> * Murali Karicheri<[email-masked]>   [150224 13:31]:
>>>> Keystone netcp driver re-uses davinci mdio driver. So enable it
>>>> by default for keystone netcp driver.
>>>>
>>>> Signed-off-by: Murali Karicheri<[email-masked]>
>>>> ---
>>>>   drivers/net/ethernet/ti/Kconfig |    1 +
>>>>   1 file changed, 1 insertion(+)
>>>>
>>>> diff --git a/drivers/net/ethernet/ti/Kconfig b/drivers/net/ethernet/ti/Kconfig
>>>> index 3bc992c..945a221 100644
>>>> --- a/drivers/net/ethernet/ti/Kconfig
>>>> +++ b/drivers/net/ethernet/ti/Kconfig
>>>> @@ -88,6 +88,7 @@ config TI_CPTS
>>>>   config TI_KEYSTONE_NETCP
>>>>   	tristate "TI Keystone NETCP Core Support"
>>>>   	select TI_CPSW_ALE
>>>> +	select TI_DAVINCI_MDIO
>>>>   	depends on OF
>>>>   	depends on KEYSTONE_NAVIGATOR_DMA&&   KEYSTONE_NAVIGATOR_QMSS
>>>>   	---help---
>>>
>>> These options should be silent Kconfig options if we're selecting
>>> them. Or else you should use depends on instead.
>>>
>> Just followed the existing implementation as it made sense.
>>
>> config TI_DAVINCI_EMAC
>> 	tristate "TI DaVinci EMAC Support"
>> 	depends on ARM&&  ( ARCH_DAVINCI || ARCH_OMAP3 )
>> 	select TI_DAVINCI_MDIO
>> 	select TI_DAVINCI_CPDMA
>> 	select PHYLIB
>> 	---help---
>> 	  This driver supports TI's DaVinci Ethernet .
>>
>> 	  To compile this driver as a module, choose M here: the module
>> 	  will be called davinci_emac_driver.  This is recommended.
>>
>> config TI_CPSW
>> 	tristate "TI CPSW Switch Support"
>> 	depends on ARCH_DAVINCI || ARCH_OMAP2PLUS
>> 	select TI_DAVINCI_CPDMA
>> 	select TI_DAVINCI_MDIO
>> 	select TI_CPSW_PHY_SEL
>> 	select TI_CPSW_ALE
>> 	select MFD_SYSCON
>> 	select REGMAP
>> 	---help---
>> 	  This driver supports TI's CPSW Ethernet Switch.
>>
>> 	  To compile this driver as a module, choose M here: the module
>> 	  will be called cpsw.
>>
>> Why it has to be silent options?
>
> Because we are now force selecting items that may have other
> dependencies later on that will not be satisfied. That causes
> all kinds of make randconfig build errors.
My mistake.  I didn't ask you what is your definition of a silent 
option? An option not selected by any other option? Or an option for 
which default value not defined? Can you clarify this so that I can make 
sense of your comment? I checked Documentation/kbuild/kconfig.txt as 
well as Documentation/kbuild/kconfig-language.txt for defintion, but 
can't find it.

Howeve, I read the warning about using "select" in the above document 
since it blindly select the option without checking dependencies. So 
AFAIK, select becomes an issue if the config option is not the leaf 
option of the config tree as the dependency checking is not in place and 
can cause issues. In this case it is safe as DAVINCI_MDIO is a leaf 
option and only selects PHYLIB which dependents on NETDEVICES and we 
know this is true for NETCP devices. So select is just fine here.

>
>> NetCP driver would require DAVINCI_MDIO driver to function.
>> So "select" make sense to me instead of "depend". How do
>> you think depend can be used here?
>
> In that case you'd have to have things the other way around:
>
> config TI_CPSW
> 	tristate "TI CPSW Switch Support"
> 	depends on ARCH_DAVINCI || ARCH_OMAP2PLUS || \
> 		TI_DAVINCI_CPDMA || TI_DAVINCI_MDIO || \
> 		TI_CPSW_PHY_SEL || TI_CPSW_ALE || \
> 		MFD_SYSCON || REGMAP
>
> But I think it's best to make these options silent Kconfig
> options so the consumer drivers can select whatever components
> they need to use. There should not be any need for users to
> have to select these options.

Users don't select any option other than NETCP. User may not need to 
know what are all the hardware drivers required to enable NETCP device 
on the platform and it is best to describe that through Kconfig instead 
of putting the burden on the user. Though select has limitations, AFAIK 
it doesn't apply here.

Thanks

Murali
> Regards,
> Tony

-- 
Murali Karicheri
Linux Kernel, Texas Instruments