Re: amba-pl011 complains about DMA for bcm2835 where it is not supported

["Piotr Król" <piotr.krol@3mdeb.com>]

On Mon, Oct 27, 2014 at 11:59:42PM +0000, Russell King - ARM Linux wrote:
> On Tue, Oct 28, 2014 at 12:44:31AM +0100, Piotr Król wrote:
> > Hi all,
> > according to BCM2835 ARM Peripherals spec DMA is optional functionality
> > for ARM PL011 UART and it is not supported on this SoC. It looks like
> > amba-pl011 search for device tree property (dma-names) unconditionally,
> > what leads to error message:
> > 
> > of_dma_request_slave_channel: dma-names property of node '/soc/uart@7e201000' missing or empty
> > uart-pl011 20201000.uart: no DMA platform data
> > 
> > I assume that if it is possible that amba-pl011 can be without DMA we
> > should check if DMA is supported and then try to read properties. Is
> > there any known method for checking dma support ? If yes that I would be
> > glad for any pointers.
> > 
> > Let me know if I should ignore/accept this error message or there is
> > some code fix needed.
> 
> A great many implementations of PL011 do not have DMA support (some have
> DMA support but its well broken.)  The driver has always supported PIO
> mode, and continues to do so.
> 

Driver works fine but IMHO this error message confuse user. Should I assume
that error message is expected and we should not avoid it by trying to
check if DMA is supported ?

BTW above error message do not indicate that DMA is not supported but
indicates that something is wrong with DT, what in this case is not true.

Thanks,
Piotr Król


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