From mboxrd@z Thu Jan 1 00:00:00 1970 From: arnd@arndb.de (Arnd Bergmann) Date: Wed, 18 Nov 2015 22:06:36 +0100 Subject: [PATCH] usb: musb: USB_TI_CPPI41_DMA requires dmaengine support In-Reply-To: References: <4370741.70D0kgBgnp@wuerfel> <3958456.qUtBLJFy2S@wuerfel> Message-ID: <4749121.AD5OMAAsPq@wuerfel> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Wednesday 18 November 2015 14:39:10 Bin Liu wrote: > > 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. That would cause a runtime failure, just like any other configuration that does not enable all the hardware you want to use. > 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... There are hundreds of device drivers that use dmaengines as a backend, we don't normally document this, just like we don't document the fact that you need to enable the right gpio, irqchip, timer, clock etc drivers for your platform. Arnd