On 24/02/2022 22:10, Rob Herring wrote:
On Thu, Feb 17, 2022 at 01:48:34PM +0000, Richard Fitzgerald wrote:
Some audio hardware cannot support a fixed slot width or a slot width equal to the sample width in all cases. This is usually due either to limitations of the audio serial port or system clocking restrictions.
This property allows setting a mapping of sample widths and the corresponding tdm slot widths.
Signed-off-by: Richard Fitzgerald rf@opensource.cirrus.com
.../devicetree/bindings/sound/audio-graph-port.yaml | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/Documentation/devicetree/bindings/sound/audio-graph-port.yaml b/Documentation/devicetree/bindings/sound/audio-graph-port.yaml index 476dcb49ece6..420adad49382 100644 --- a/Documentation/devicetree/bindings/sound/audio-graph-port.yaml +++ b/Documentation/devicetree/bindings/sound/audio-graph-port.yaml @@ -71,4 +71,11 @@ patternProperties: description: CPU to Codec rate channels. $ref: /schemas/types.yaml#/definitions/uint32
dai-tdm-slot-width-map:description: Mapping of sample widths to slot widths. For hardware thatcannot support a fixed slot width or a slot width equal to sampleA variable slot width sounds like a feature, not a limitation.
Depends on point of view. Most interfaces allow setting a fixed slot width but in some cases that's not possible so it is more likely to be seen as a limitation. It is however a feature in the sense that it can avoid using higher frequencies that are necessary.
width. An array containing one or more pairs of values. Each pairof values is a sample_width and the corresponding slot_width.That sounds like a matrix, not an array. N entries of 2 cells each.
$ref: /schemas/types.yaml#/definitions/uint32-arrayI'd think there are some constraints on the values? Slots should be at least 8 bits, right? A max of 2x32 bits or is there more
True. I didn't think it was appropriate for a generic binding to enforce a range when that depends on the exact hardware. But if you want I can enforce a range that's likely to be true for all hardware.
than stereo within a slot? In any case, it's for sure no where near 2^32 max.
One sample per slot.
Is there a need for specifying where in the slot the data is?
I don't believe so, all the protocols I know of have the data bits transmitted first followed by padding. There's no harm adding a reserved field to allow for this info if it is ever needed, but it would be unused at present as there's no kernel API to do this.
Rob