Re: [PATCH v5 00/13] Enable display support for STM32MP25

[Raphael Gallais-Pou <raphael.gallais-pou@foss.st.com>]

On 8/28/25 17:27, Philippe CORNU wrote:
>
>
> On 8/22/25 16:34, Raphael Gallais-Pou wrote:
>> This series aims to add and enable sufficient LVDS display support for
>> STM32MP257F-EV1 board.
>>
>> LVDS is the default use case to drive a display panel on STM32MP257F-EV,
>> even though DSI panels will be supported in the near future.
>>
>> The LTDC needs a pixel rate in sync with the bridge currently in use.
>> For that both DSI and LVDS bridges need to declare an internal clock and
>> become clock provider to the mux. The mux then selects the reference
>> clock for the LTDC pixel rate generation.
>>
>> For now this mux is handled internally in the LTDC, while waiting for
>> the STM32 clock framework to merge a 'clk-mux' based on the SYSCFG.
>> This explains the link done in the patch [7/8] between the LVDS,
>> providing the reference clock for the LTDC internals.
>>
>>    +----------+              |\
>>    |  DSI PHY |------------->| \           +------------+
>>    |          |ck_dsi_phy    |  |          |            |
>>    +----------+              |  |--------->|    LTDC    |
>>    +----------+              |  |pixel_clk |            |
>>    | LVDS PHY |------------->|  |          +------------+
>>    |          |clk_pix_lvds  |  |
>>    +----------+              |  |
>>                              |  |
>>     ck_ker_ltdc ------------>| /
>>                              |/|
>>                                └- SYSCFG
>>
>> Clock selection applies as follow:
>> - 0b00: Selects ck_dsi_phy
>> - 0b01: Selects clk_pix_lvds
>> - 0b10: Selects ck_ker_ltdc (for parallel or DSI display).
>> - 0b11: Reserved
>>
>> The reset value of the register controlling the mux is 0b01, meaning
>> that the default clock assigned is the clk_pix_lvds.  This causes two
>> things:
>>
>> - In order to get basic display on the LVDS encoder, like intended,
>> nothing has to be done on this mux within the LTDC driver (which for now
>> explains the unused syscfg phandle on the LTDC node in the device-tree).
>>
>> - 'pixel_clk' is dependent from 'clk_pix_lvds' because of the LTDC clock
>> domains.  They also need to be sync to get a coherent pixel rate though
>> the display clock tree (which explains the LVDS phandle on the LTDC node
>> in the device-tree).
>>
>> Signed-off-by: Raphael Gallais-Pou <raphael.gallais-pou@foss.st.com>
>> ---
>> Changes in v5:
>> - Documentation:
>>    - LTDC: Clamp correctly min/maxItems value (again)
>> - Add Yannick's trailers where relevant except in patch [01/13] which
>>    has been modified
>> - Link to v4:
>> https://lore.kernel.org/r/20250821-drm-misc-next-v4-0-7060500f8fd3@foss.st.com
>>
>> Changes in v4:
>> - Documentation:
>>    - LTDC: Add "st,stm32mp255-ltdc" compatible.  After internal
>>      discussion, we came to the solution that the LTDC on STM32MP255 SoC
>>      needs its own compatible, since it does have the same amount of
>>      clocks than on STM32MP251 SoC.
>> - Devicetree:
>>    - Add "st,stm32mp255" compatible on corresponding dtsi
>> - Drivers:
>>    - LTDC: Handle "st,stm32mp255" compatible
>> - Remove Rob's r-b from patch [01/13] since it was modified.
>> - Link to v3:
>> https://lore.kernel.org/r/20250819-drm-misc-next-v3-0-04153978ebdb@foss.st.com
>>
>> Changes in v3:
>> - Rebased on latest drm-misc-next
>> - Documentation:
>>    - LTDC: Clamp correctly min/maxItems value
>>    - LVDS: Remove second 'items' keyword
>> - Add Krzysztof's trailer where relevant
>> - Link to v2:
>> https://lore.kernel.org/r/20250812-drm-misc-next-v2-0-132fd84463d7@foss.st.com
>>
>> Changes in v2:
>> - Documentation:
>>    - Add support for new compatible "st,stm32mp255-lvds"
>>    - Change LTDC compatible for SoC compliant one
>>    - Make clearer LTDC clock-names property
>> - Devicetree:
>>    - Change compatible according to the documentation
>>    - Change clock and clock-names order to match documentation (and avoid
>>      warnings)
>> - Drivers:
>>    - Change LTDC compatible
>> - Add Rob's trailer where relevant
>> - Link to v1:
>> https://lore.kernel.org/r/20250725-drm-misc-next-v1-0-a59848e62cf9@foss.st.com
>>
>> ---
>> Raphael Gallais-Pou (11):
>>        dt-bindings: display: st: add two new compatibles to LTDC device
>>        dt-bindings: display: st,stm32-ltdc: add access-controllers property
>>        dt-bindings: display: st: add new compatible to LVDS device
>>        dt-bindings: display: st,stm32mp25-lvds: add access-controllers property
>>        dt-bindings: display: st,stm32mp25-lvds: add power-domains property
>>        dt-bindings: arm: stm32: add required #clock-cells property
>>        arm64: dts: st: add ltdc support on stm32mp251
>>        arm64: dts: st: add ltdc support on stm32mp255
>>        arm64: dts: st: add lvds support on stm32mp255
>>        arm64: dts: st: add clock-cells to syscfg node on stm32mp251
>>        arm64: dts: st: enable display support on stm32mp257f-ev1 board
>>
>> Yannick Fertre (2):
>>        drm/stm: ltdc: support new hardware version for STM32MP25 SoC
>>        drm/stm: ltdc: handle lvds pixel clock
>>
>>   .../bindings/arm/stm32/st,stm32-syscon.yaml        | 31 ++++++---
>>   .../devicetree/bindings/display/st,stm32-ltdc.yaml | 55 ++++++++++++++-
>>   .../bindings/display/st,stm32mp25-lvds.yaml        | 13 +++-
>>   arch/arm64/boot/dts/st/stm32mp251.dtsi             | 19 ++++++
>>   arch/arm64/boot/dts/st/stm32mp255.dtsi             | 20 +++++-
>>   arch/arm64/boot/dts/st/stm32mp257f-ev1.dts         | 79 ++++++++++++++++++++++
>>   drivers/gpu/drm/stm/drv.c                          | 12 +++-
>>   drivers/gpu/drm/stm/ltdc.c                         | 58 +++++++++++++++-
>>   drivers/gpu/drm/stm/ltdc.h                         |  6 ++
>>   9 files changed, 275 insertions(+), 18 deletions(-)
>> ---
>> base-commit: c8cea4371e5eca30cda8660aabb337747dabc51d
>> change-id: 20250617-drm-misc-next-4af406c1c45f
>>
>> Best regards,
>
> Hi Raphael,
> Thank you for these great patches.
>
> If you agree, I think you can merge 01-08 in misc.

Hi Philippe,

Applied patches [01/13] -> [08/13] on drm-misc-next.

Thanks,
Best regards,
Raphaël
>
> Best regards
> Philippe :-)