On 17-01-19, 09:43, John Stultz wrote: > On Thu, Jan 17, 2019 at 9:08 AM Manivannan Sadhasivam > <manivannan.sadhasivam@xxxxxxxxxx> wrote: > > > > On Wed, Jan 16, 2019 at 09:10:23AM -0800, John Stultz wrote: > > > Some dma channels can be reserved for secure mode or other > > > hardware on the SoC, so provide a binding for a bitmask > > > listing the available channels for the kernel to use. > > > > > > This follows the pre-existing bcm,dma-channel-mask binding. > > > > > > Cc: Vinod Koul <vkoul@xxxxxxxxxx> > > > Cc: Rob Herring <robh+dt@xxxxxxxxxx> > > > Cc: Mark Rutland <mark.rutland@xxxxxxx> > > > Cc: Tanglei Han <hantanglei@xxxxxxxxxx> > > > Cc: Zhuangluan Su <suzhuangluan@xxxxxxxxxxxxx> > > > Cc: Ryan Grachek <ryan@xxxxxxxxx> > > > Cc: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx> > > > Cc: dmaengine@xxxxxxxxxxxxxxx > > > Cc: devicetree@xxxxxxxxxxxxxxx > > > Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx> > > > --- > > > v3: Renamed to hisi-dma-avail-chan > > > v4: Reworked to generic dma-channel-mask > > > --- > > > Documentation/devicetree/bindings/dma/dma.txt | 4 ++++ > > > 1 file changed, 4 insertions(+) > > > > > > diff --git a/Documentation/devicetree/bindings/dma/dma.txt b/Documentation/devicetree/bindings/dma/dma.txt > > > index 6312fb0..eeb4e4d 100644 > > > --- a/Documentation/devicetree/bindings/dma/dma.txt > > > +++ b/Documentation/devicetree/bindings/dma/dma.txt > > > @@ -16,6 +16,9 @@ Optional properties: > > > - dma-channels: Number of DMA channels supported by the controller. > > > - dma-requests: Number of DMA request signals supported by the > > > controller. > > > +- dma-channel-mask: Bitmask of available DMA channels in ascending order > > > + that are not reserved by firmware and are available to > > > + the kernel. i.e. first channel corresponds to LSB. > > > > A general assumption is, "dma-channel-mask" refers to the bit fields of > > the channels which needs to be masked. But here, it refers to the channels > > which are available. Doesn't it contradict? > > Hrm. So while I can sort of understand the common usage of "mask" as > to "hide", thus the desire to have a bitfield mean "the channels we > hide" or "don't use", but in my experience bitmasking is more commonly > used to keep only a portion of the the bits, so from that perspective > its more intuitive that a mask be the channels we keep to use. So I'm > not sure if your suggestion makes it more clear. > > But I'm not very particular here, so I'll defer to others on this. Given the context and documentation which explicitly says it is bitmask of available channels, i think we are fine :) -- ~Vinod
