linux-kernel - Re: [PATCH] usb: musb: USB_TI_CPPI41

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Date:	Wed, 18 Nov 2015 14:38:36 -0600
From:	Felipe Balbi <balbi@...com>
To:	Bin Liu <binmlist@...il.com>
CC:	Arnd Bergmann <arnd@...db.de>, <linux-usb@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] usb: musb: USB_TI_CPPI41_DMA requires dmaengine support


Hi,

Bin Liu <binmlist@...il.com> writes:
>> Bin Liu <binmlist@...il.com> writes:
>>> On Wed, Nov 18, 2015 at 10:18 AM, Arnd Bergmann <arnd@...db.de> wrote:
>>>> The CPPI-4.1 driver selects TI_CPPI41, which is a dmaengine
>>>> driver and that may not be available when CONFIG_DMADEVICES
>>>> is not set:
>>>>
>>>> warning: (USB_TI_CPPI41_DMA) selects TI_CPPI41 which has unmet direct dependencies (DMADEVICES && ARCH_OMAP)
>>>>
>>>> This adds an extra dependency to avoid generating warnings in randconfig
>>>> builds. Ideally we'd remove the 'select' statement, but that has the
>>>> potential to break defconfig files.
>>>>
>>>> Signed-off-by: Arnd Bergmann <arnd@...db.de>
>>>> Fixes: 411dd19c682d ("usb: musb: Kconfig: Select the DMA driver if DMA mode of MUSB is enabled")
>>>>
>>>> diff --git a/drivers/usb/musb/Kconfig b/drivers/usb/musb/Kconfig
>>>> index 1f2037bbeb0d..45c83baf675d 100644
>>>> --- a/drivers/usb/musb/Kconfig
>>>> +++ b/drivers/usb/musb/Kconfig
>>>> @@ -159,7 +159,7 @@ config USB_TI_CPPI_DMA
>>>>
>>>>  config USB_TI_CPPI41_DMA
>>>>         bool 'TI CPPI 4.1 (AM335x)'
>>>> -       depends on ARCH_OMAP
>>>> +       depends on ARCH_OMAP && DMADEVICES
>>>>         select TI_CPPI41
>>>
>>> I am not sure what the generic policy is, but instead of hiding
>>> USB_TI_CPPI41_DMA if DMADEVICES is disabled, I'd like to enable
>>> DMADEVICES if USB_TI_CPPI41_DMA is enabled, from user experience
>>> perspective.
>>
>> that would mean "select DMADEVICES" and that's frowned upon.
>
> Currently 'select DMADEVICES' is not in there. Will adding it fix the
> dependency warning in randconfig? Sorry for the question, but I don't
> know enough about Kconfig to get the answer.

it certainly would, but we don't like to add "select XYZ" to Kconfig
because a select bypasses the dependency tree. Let me explain:

config A
       tristate "A"
       depends on B

config B
       tristate "B"


config C
       tristate "C"
       select A


C can select A without B being enabled.

-- 
balbi

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