Re: [PATCH v2 4/8] dt-bindings: serial: Add support for selecting data transfer mode

On 27.01.2025 6:50 PM, Konrad Dybcio wrote:

On 27.01.2025 5:24 PM, Krzysztof Kozlowski wrote:

quoted

On 27/01/2025 15:27, Dmitry Baryshkov wrote:

quoted

On Mon, Jan 27, 2025 at 08:02:12AM +0100, Krzysztof Kozlowski wrote:

quoted

On 24/01/2025 11:53, Viken Dadhaniya wrote:

quoted

Data transfer mode is fixed by TrustZone (TZ), which currently restricts
developers from modifying the transfer mode from the APPS side.

Document the 'qcom,xfer-mode' properties to select the data transfer mode,
either GPI DMA (Generic Packet Interface) or non-GPI mode (PIO/CPU DMA).

UART controller can operate in one of two modes based on the
'qcom,xfer-mode' property, and the firmware is loaded accordingly.

Co-developed-by: Mukesh Kumar Savaliya <redacted>
Signed-off-by: Mukesh Kumar Savaliya <redacted>
Signed-off-by: Viken Dadhaniya <redacted>
---

v1 -> v2:

- Drop 'qcom,load-firmware' property and add 'firmware-name' property in
  qup common driver.
- Update commit log.

v1 Link: https://lore.kernel.org/linux-kernel/20241204150326.1470749-4-quic_vdadhani@quicinc.com/ (local)
---
---
 .../devicetree/bindings/serial/qcom,serial-geni-qcom.yaml | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/Documentation/devicetree/bindings/serial/qcom,serial-geni-qcom.yaml b/Documentation/devicetree/bindings/serial/qcom,serial-geni-qcom.yaml
index dd33794b3534..383773b32e47 100644
--- a/Documentation/devicetree/bindings/serial/qcom,serial-geni-qcom.yaml
+++ b/Documentation/devicetree/bindings/serial/qcom,serial-geni-qcom.yaml

@@ -56,6 +56,13 @@ properties:
   reg:
     maxItems: 1
 
+  qcom,xfer-mode:
+    description: Set the value to 1 for non-GPI (FIFO/CPU DMA) mode and 3 for GPI DMA mode.
+      The default mode is FIFO.
+    $ref: /schemas/types.yaml#/definitions/uint32
+    enum: [1, 3]
+
+

Just one blank line, but anyway, this property should not be in three
places. Do you really expect that each of serial engines within one
GeniQUP will be configured differently by TZ?

Yes, each SE is configured separately and it's quite frequent when
different SEs have different DMA configuration.

Well, I checked at sm8550 and sm8650 and each pair of SE - which shares
resources - has the same DMAs, so I would not call it frequent. Care to
bring an example where same serial engines have different DMAs and
different TZ? We do not talk about single QUP.

Anyway, if you need property per node, this has to be shared schema.

I'd rather ask a different question.. Is there *any* reason to not use
DMA for protocols that support it?

If not, we can simplify this to:

xfer_mode = protocol == PROTOCOL_UART ? XFER_FIFO : XFER_DMA

Konrad