Re: [PATCH 2/3] k3dma: add support to reserved minimum channels

On 06-07-18, 11:05, Guodong Xu wrote:

On Thu, Jun 28, 2018 at 2:02 PM Vinod [off-list ref] wrote:

quoted

On 22-06-18, 11:24, Guodong Xu wrote:

quoted

From: Li Yu <redacted>

On k3 series of SoC, DMA controller reserves some channels for
other on-chip coprocessors. By adding support to dma_min_chan, kernel
will not be able to use these reserved channels.

One example is on Hi3660 platform, channel 0 is reserved to lpm3.

Please also refer to Documentation/devicetree/bindings/dma/k3dma.txt

and if some other platform has channel X marked for co-processor, maybe
a last channel or something in middle, how will this work then?

Hi， Vinod

Sorry for delayed response. We checked with Kirin hardware design
team, so far their design strategy is all Kirin SoC series reserve
only from minimum side, saying channel 0, then 1, then 2. That impacts
the current SoC in upstreaming, Kirin960 (Hi3660), and next versions
in Kirin SoC, Kirin970 and 980, which may hit upstream later.

And what guarantees that they will not change their mind..

quoted

I am thinking this should be a mask, rather than min.

So, since this driver k3dma.c is only used by Kirin SoC DMA
controllers, I would prefer to keep the current design dma_min_chan
unchanged.

What do you think?

I would still prefer bitmask to expose the channels you are supposed to
use

-- 
~Vinod