Re: [PATCH] usb: musb: USB_TI_CPPI41_DMA requires dmaengine support

From: Bin Liu
Date: Wed Nov 18 2015 - 15:39:17 EST


On Wed, Nov 18, 2015 at 2:27 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote:
> On Wednesday 18 November 2015 12:29:27 Bin Liu wrote:
>> > 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.
> General policy is that you should not 'select' a symbol that is
> also user-visible, as that tends to cause dependency loops and
> other problems when something is enabled without the user being
> aware of that.

Understood. Thanks. I am okay with this patch.

> Ideally we should remove the 'select TI_CPPI41' here as well, but
> what we could do instead is to make that a silent symbol and remove
> the prompt so it always gets enabled implicitly when USB_TI_CPPI41_DMA
> and DMADEVICES are both enabled.

But what if DMADEVICES was disabled and USB_TI_CPPI41_DMA was enabled?
I would think I had CPPI fully enabled for MUSB, but it didn't because
TI_CPPI41 was disabled.

I would think this patch is the test option so far, we might have to
document somewhere that to dmaengine has to be enabled to use MUSB
CPPI, but I am not sure where the best place is to document...


> Arnd
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