[PATCH RFC 0/4] phy: qcom-mipi-csi2: C-PHY for X1E80100

[George Neacsu <geocausa@gmail.com>]

Hi Bryan, Vinod, David,

The Snapdragon Surface Pro 11's front camera, an IMX681, is on CSIPHY2
over one MIPI C-PHY trio. linux-next has the CSI2 PHY driver and the CAMSS
PHY API path, and C-PHY is the piece still missing for this camera. This
series adds it. Before I go further, I would like to know whether this is
the shape you want:

1. PHY_MODE_MIPI_CPHY and C-PHY configuration options in the generic PHY
   framework, because CAMSS had no way to ask the PHY for C-PHY;
2. C-PHY in qcom-mipi-csi2, with the X1E80100 sequence taken from
   Qualcomm's GPL-2.0 downstream header;
3. the CSID 680 PHY type select, which is defined but never written;
4. C-PHY in csiphy_stream_on() for PHY API CSIPHYs.

The base is next-20261015 plus David's "media: camss: Add support for
C-PHY configuration on Qualcomm platforms" v9, which provides phy_cfg,
the CSID phy_sel and the C-PHY link frequency. I had to port its 8/9 by
hand onto the PHY API changes:
https://lore.kernel.org/all/20260617-qcom-cphy-v9-0-83da8a8e4e44@ixit.cz/

Tested on the Surface Pro 11 (X1E80100). Both cameras run together through
the upstream stack: CSI2 PHY nodes as in Bryan's x1e80100 camera DT v7,
and CAMSS in PHY API mode, with raw capture over RDI:
- front IMX681 (Sergey's and Andre's v8 driver plus its C-PHY RFC) on
  CSIPHY2, one C-PHY trio at 2.4 Gsym/s: 3844x2640 at 30.01 fps, and the
  sensor's colour bars are byte-identical to the pattern captured with an
  out-of-tree driver;
- rear OV13858 on CSIPHY1, four D-PHY lanes: 29.9 fps, as before the
  series.
The kernel was 7.1.5, with linux-next's CAMSS and CSI2 PHY built as
modules; the test build needed shims only for API differences.

Two questions:
- Is a generic C-PHY mode how you want CAMSS to ask for it, or would you
  rather the PHY take the mode from its own endpoint alone?
- Qualcomm's X1E sequence is for 2.5 Gsps, and this sensor runs at
  2.4 Gsym/s with it. The sa8775p C-PHY series selects settings by data
  rate. Should X1E do the same?

Patches 1-2 are PHY and 3-4 are CAMSS. They can go separately once the
approach is agreed.

Thanks,
George

---
George Neacsu (4):
      phy: Add MIPI C-PHY mode and configuration options
      phy: qcom-mipi-csi2: Add C-PHY support for X1E80100
      media: qcom: camss: csid-680: Select C-PHY in the receiver
      media: qcom: camss: Configure C-PHY through the PHY API

 drivers/media/platform/qcom/camss/camss-csid-680.c |   2 +
 drivers/media/platform/qcom/camss/camss-csiphy.c   |  35 +++--
 drivers/phy/qualcomm/phy-qcom-mipi-csi2-3ph-dphy.c | 151 ++++++++++++++++++++-
 drivers/phy/qualcomm/phy-qcom-mipi-csi2-core.c     |  49 ++++++-
 drivers/phy/qualcomm/phy-qcom-mipi-csi2.h          |   4 +
 include/linux/phy/phy-mipi-cphy.h                  |  27 ++++
 include/linux/phy/phy.h                            |   5 +
 7 files changed, 252 insertions(+), 21 deletions(-)
---
base-commit: 4a926a0ea6c65089285eb3ccb84ac6b02b22dee5
change-id: 20261015-x1e-cphy-rfc-201860c8097f

Best regards,
-- 
George Neacsu <geocausa@gmail.com>