linux-kernel - Re: [PATCH 4/5] dt-bindings: dma: ti-edma: Add option for reserved channel ranges

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Date:   Fri, 6 Sep 2019 14:10:25 +0100
From:   Rob Herring <robh@...nel.org>
To:     Peter Ujfalusi <peter.ujfalusi@...com>
Cc:     Vinod <vkoul@...nel.org>, Dan Williams <dan.j.williams@...el.com>,
        "open list:DMA GENERIC OFFLOAD ENGINE SUBSYSTEM" 
        <dmaengine@...r.kernel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>, devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-omap <linux-omap@...r.kernel.org>
Subject: Re: [PATCH 4/5] dt-bindings: dma: ti-edma: Add option for reserved
 channel ranges

On Tue, Sep 3, 2019 at 11:19 AM Peter Ujfalusi <peter.ujfalusi@...com> wrote:
>
> Hi Rob,
>
> On 30/08/2019 8.37, Peter Ujfalusi wrote:
> > Rob,
> >
> > On 30/08/2019 1.47, Rob Herring wrote:
> >> On Fri, Aug 23, 2019 at 03:56:17PM +0300, Peter Ujfalusi wrote:
> >>> Similarly to paRAM slots, channels can be used by other cores.
> >>>
> >>> Add optional property to configure the reserved channel ranges.
> >>>
> >>> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@...com>
> >>> ---
> >>>  Documentation/devicetree/bindings/dma/ti-edma.txt | 5 +++++
> >>>  1 file changed, 5 insertions(+)
> >>>
> >>> diff --git a/Documentation/devicetree/bindings/dma/ti-edma.txt b/Documentation/devicetree/bindings/dma/ti-edma.txt
> >>> index 4bbc94d829c8..1198682ada99 100644
> >>> --- a/Documentation/devicetree/bindings/dma/ti-edma.txt
> >>> +++ b/Documentation/devicetree/bindings/dma/ti-edma.txt
> >>> @@ -42,6 +42,9 @@ Optional properties:
> >>>  - ti,edma-reserved-slot-ranges: PaRAM slot ranges which should not be used by
> >>>             the driver, they are allocated to be used by for example the
> >>>             DSP. See example.
> >>> +- ti,edma-reserved-chan-ranges: channel ranges which should not be used by
> >>> +           the driver, they are allocated to be used by for example the
> >>> +           DSP. See example.
> >>
> >> Based on the other thread, I think extending dma-channel-mask to a
> >> uint32-array makes sense here.
> >
> > Yes, that is the reason I have asked on that and I'm in progress of
> > converting the edma driver to use the dma-channel-mask.
> > Just need to do some shuffling in the driver to get the mask in a form
> > usable by the driver.
> >
> > I'll send an updated series early next week.
>
> How should the dma-channel-mask uint31-array should be documented and used?
>
> Basically some EDMA have 32, some 64 channels. This is fine.
> Let's say I want to mask out channel 0-4 and 24-27
>
> This would look like in case of EDMA with 32 channels:
> &edma {
>         /* channel 0-4 and 24-27 is not to be used */
>         dma-channel-mask = <0xf0fffff0>;
> };
>
> How this should look like in case when I have 64 channels?
> &edma {
>         /* channel 0-4 and 24-27 is not to be used */
>         dma-channel-mask = <0xf0fffff0>, <0xffffffff>;
> };
>
> When I read the u32s then
> chan_mask[0] is for channel 0-31 (LSB is channel 0)
> chan_maks[1] is for channel 32-63 (LSB is channel 32)
>
> Or:
> &edma {
>         /* channel 0-4 and 24-27 is not to be used */
>         dma-channel-mask = <0xffffffff>, <0xf0fffff0>;
> };
>
> chan_maks[0] is for channel 32-63 (LSB is channel 32)
> chan_mask[1] is for channel 0-31 (LSB is channel 0)
>
> Do you have pointer on already established notion on how to document and
> handle this?

As far as word ordering, I guess you can do whatever order you want.
MSB first would make the most sense if this was only going to be up to
64-bit. But given it could be 96, 128, ... bits, probably the least
significant word first makes sense and is easier to parse for a
variable length.

The binding schema can be something like this:

items:
  - description: Mask of channels 0-31
  - description: Mask of channels 32-63

The length is implied by the number of list items.

Rob