Re: [RFC PATCH 7/8] dt-bindings: sound: qcom: add Tambora WCD9378 SDCA codec

[Krzysztof Kozlowski <krzk@kernel.org>]

On 29/07/2026 14:36, Srinivas Kandagatla wrote:
> On 7/29/26 1:30 PM, Krzysztof Kozlowski wrote:
>> On 29/07/2026 14:17, Srinivas Kandagatla wrote:
>>> On 7/29/26 12:40 PM, Krzysztof Kozlowski wrote:
>>>> On 23/07/2026 01:42, Srinivas Kandagatla wrote:
>>>>> Describe the WCD9378 SDCA peripheral node (compatible sdw20217011000)
>>>>> driven by the wcd9378-sdca codec driver for headphone playback, headset
>>>>> mic capture and jack detection via the SimpleJack SDCA function type.
>>>>>
>>>>> WCD9378 codec can be wired up in 2 different modes.
>>>>> "mobile mode" on phone/tablet SoCs is enumerated as tx and rx device,
>>>>> each of which has dedicated control and data lines.
>>>>> "compute mode" on compute platforms such as Glymur is enumerated as
>>>>> single standard MIPI SDCA class device.
>>>>>
>>>>> Both modes share same Device ID, compatible; qcom,compute-mode selects
>>>>> which driver path is taken.  Supplies, reset GPIO and mic-bias voltages
>>>>> live on the SoundWire slave node in compute mode and are forbidden in
>>>>> mobile mode (owned by the top-level codec parent there).
>>>>>
>>>>> Assisted-by: Claude:claude-opus-4-7
>>>>> Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@oss.qualcomm.com>
>>>>> ---
>>>>>  .../bindings/sound/qcom,wcd9378-sdw.yaml      | 200 ++++++++++++++++++
>>>>>  1 file changed, 200 insertions(+)
>>>>>  create mode 100644 Documentation/devicetree/bindings/sound/qcom,wcd9378-sdw.yaml
>>>>>
>>>>> diff --git a/Documentation/devicetree/bindings/sound/qcom,wcd9378-sdw.yaml b/Documentation/devicetree/bindings/sound/qcom,wcd9378-sdw.yaml
>>>>> new file mode 100644
>>>>> index 000000000000..2ed4ad92958e
>>>>> --- /dev/null
>>>>> +++ b/Documentation/devicetree/bindings/sound/qcom,wcd9378-sdw.yaml
>>>>> @@ -0,0 +1,200 @@
>>>>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>>>>> +%YAML 1.2
>>>>> +---
>>>>> +$id: http://devicetree.org/schemas/sound/qcom,wcd9378-sdw.yaml#
>>>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>>>> +
>>>>> +title: Qualcomm SoundWire Slave devices on WCD9378
>>>>> +
>>>>> +maintainers:
>>>>> +  - Jorijn van der Graaf <jorijnvdgraaf@catcrafts.net>
>>>>> +  - Srinivas Kandagatla <srinivas.kandagatla@oss.qualcomm.com>
>>>>> +
>>>>> +description: |
>>>>> +  The Qualcomm WCD9378 codec presents its SoundWire slave devices with
>>>>> +  class ID sdw20217011000 in both operating modes:
>>>>> +
>>>>> +    * mobile mode -- two slave instances sit on separate SoundWire
>>>>> +      masters carrying data only.  A separate top-level codec node
>>>>> +      owns the codec's supplies, mic-bias voltages and reset GPIO.
>>>>> +
>>>>> +    * SDCA / compute mode -- one aggregated slave sits on a multi-lane
>>>>> +      master and carries both control and data.  There is no separate
>>>>> +      top-level codec node, so the SoundWire slave node itself owns
>>>>> +      supplies, reset GPIO and mic-bias voltage configuration.  It is
>>>>> +      marked with qcom,compute-mode.
>>>>> +
>>>>> +  Codec drivers that match sdw20217011000 use qcom,compute-mode to
>>>>> +  decide which mode to serve; the presence or absence of this property
>>>>> +  also gates whether the supply and mic-bias properties on this node
>>>>> +  are required or forbidden.
>>>>> +
>>>>> +properties:
>>>>> +  compatible:
>>>>> +    const: sdw20217011000
>>>>> +
>>>>> +  reg:
>>>>> +    maxItems: 1
>>>>> +
>>>>> +  qcom,compute-mode:
>>>>> +    description: |
>>>>> +      Marks this SoundWire slave as the single aggregated slave that
>>>>> +      implements the codec in SDCA / compute mode.  Only present when
>>>>> +      the codec has no separate top-level codec parent; in that case
>>>>> +      this slave node also owns the codec's supplies, reset GPIO and
>>>>> +      mic-bias voltage configuration.  Absent in mobile mode.
>>>>
>>>> I doubt there is really "compute" or "mobile" mode, so you just wrote to
>>>> match use case, but that does not match hardware.
>>>>
>>> This is hardware fuse setting, its not just usecase based but it changes
>>> complete wcd9378 hardware topology, in mobile mode we have 2 soundwire
>>> devices representing tx and rx side of wcd9378 however in compute mode
>>> it only has one soundwire device dealing with both tx and rx. compute
>>> mode is sdca class compliant device.
>>>
>>>
>>>> I think there should be no separate top-level codec parent in the first
>>>> place, thus this property is not needed. You always list here all resources.
>>> There is no top level aggregated device when the codec is fused in
>>> compute mode.
>>
>> There should not be a top-level in either case. This was always Linux
>> driver limitation.
> 
> That is not true, its clearly a hardware topology thing.
> Codec has two devices tx and rx, Only one of the device (tx) has access
> to CSR registers of the codec, so rx and tx are pretty much a single
> aggregate codec device which is why we have top-level representation of
> the aggregate device.

So two devices, but not three. If TX has access to RX, it does not mean
there is third device. If there was a third device (that top level
thingy) you would have it here as well. You don't have, because it is
purely for Linux.

Best regards,
Krzysztof