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

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Date:	Wed, 18 Nov 2015 14:45:32 -0600
From:	Bin Liu <binmlist@...il.com>
To:	Felipe Balbi <balbi@...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

On Wed, Nov 18, 2015 at 2:38 PM, Felipe Balbi <balbi@...com> wrote:
>
> 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.

Thanks for the explanation, very clear.

>
> --
> balbi
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