Re: [PATCH 00/16] STM32 configure UART nodes for DMA

Hello Erwan,

On 03.02.22 18:10, Erwan Le Ray wrote:

Add DMA configuration to UART nodes in stm32mp15x (SOC level) and
remove it at board level to keep current PIO behavior when needed.
For stm32-ed1 and stm32-dkx boards, UART4 (console) and UART7
(no HW flow control pin available) are kept in PIO mode, while USART3
is now configured in DMA mode.
UART4 (console UART) has to be kept in irq mode, as DMA support for
console has been removed from the driver by commit e359b4411c28 
("serial: stm32: fix threaded interrupt handling"). 

Do I understand correctly that your first patch breaks consoles of
most/all boards, because they will briefly use DMA, which is refused
by the stm32-usart driver and then you add a patch for each board
to fix that breakage?

Such intermittent breakage makes bisection a hassle. /delete-property/
is a no-op when the property doesn't exist, so you could move the first
patch to the very end to avoid intermittent breakage.

I also think that the driver's behavior is a bit harsh. I think it would
be better for the UART driver to print a warning and fall back to
PIO for console instead of outright refusing and rendering the system
silent. That's not mutually exclusive with your patch series here, of course.

Cheers,
Ahmad

For other stm32mp15x-based boards, current configuration is kept for
all UART instances.

Erwan Le Ray (16):
  ARM: dts: stm32: add DMA configuration to UART nodes on stm32mp151
  ARM: dts: stm32: keep uart4 behavior on stm32mp157c-ed1
  ARM: dts: stm32: keep uart4 and uart7 behavior on stm32mp15xx-dkx
  ARM: dts: stm32: keep uart4 behavior on icore-stm32mp1-ctouch2
  ARM: dts: stm32: keep uart4 behavior on icore-stm32mp1-edimm2.2
  ARM: dts: stm32: keep uart4 behavior on stm32mp157a-iot-box
  ARM: dts: stm32: keep uart nodes behavior on stm32mp1-microdev2.0-of7
  ARM: dts: stm32: keep uart nodes behavior on stm32mp1-microdev2.0
  ARM: dts: stm32: keep uart nodes behavior on stm32mp157a-stinger96
  ARM: dts: stm32: keep uart4 behavior on stm32mp157c-lxa-mc1
  ARM: dts: stm32: keep uart4 behavior on stm32mp157c-odyssey
  ARM: dts: stm32: keep uart nodes behavior on stm32mp15xx-dhcom-drc02
  ARM: dts: stm32: keep uart nodes behavior on stm32mp15xx-dhcom-pdk2
  ARM: dts: stm32: keep uart nodes behavior on stm32mp15xx-dhcom-picoitx
  ARM: dts: stm32: keep uart4 behavior on stm32mp15xx-dhcom-som
  ARM: dts: stm32: keep uart nodes behavior on
    stm32mp15xx-dhcor-avenger96

 arch/arm/boot/dts/stm32mp151.dtsi             | 21 +++++++++++++++++++
 .../stm32mp157a-icore-stm32mp1-ctouch2.dts    |  2 ++
 .../stm32mp157a-icore-stm32mp1-edimm2.2.dts   |  2 ++
 arch/arm/boot/dts/stm32mp157a-iot-box.dts     |  2 ++
 ...157a-microgea-stm32mp1-microdev2.0-of7.dts |  4 ++++
 ...32mp157a-microgea-stm32mp1-microdev2.0.dts |  4 ++++
 arch/arm/boot/dts/stm32mp157a-stinger96.dtsi  |  6 ++++++
 arch/arm/boot/dts/stm32mp157c-ed1.dts         |  2 ++
 arch/arm/boot/dts/stm32mp157c-lxa-mc1.dts     |  2 ++
 arch/arm/boot/dts/stm32mp157c-odyssey.dts     |  2 ++
 .../arm/boot/dts/stm32mp15xx-dhcom-drc02.dtsi |  4 ++++
 arch/arm/boot/dts/stm32mp15xx-dhcom-pdk2.dtsi |  4 ++++
 .../boot/dts/stm32mp15xx-dhcom-picoitx.dtsi   |  4 ++++
 arch/arm/boot/dts/stm32mp15xx-dhcom-som.dtsi  |  2 ++
 .../boot/dts/stm32mp15xx-dhcor-avenger96.dtsi |  6 ++++++
 arch/arm/boot/dts/stm32mp15xx-dkx.dtsi        |  4 ++++
 16 files changed, 71 insertions(+)

-- 
Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |