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

[Erwan LE RAY]

Hi Ahmad,


On 2/4/22 2:22 PM, Alexandre TORGUE wrote:
> Hi Ahmad
>
> On 2/3/22 18:25, Ahmad Fatoum wrote:
> > 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?
>
> We have two solutions and both have pro/drawbacks. The first one (Erwan 
> ones, can break the boot if the patch is taken "alone". Your proposition 
> avoids this breakage but deletes a non define property (which is a bit 
> weird). However I prefer to keep a functional behavior, and keep Ahmad 
> proposition. Ahmad, just one question, dt-bindings check doesn't 
> complain about it ?
>
> Cheers
> Alex
>
> > 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

The driver implementation will consider the request to probe the UART 
console in DMA mode as an error (-ENODEV), and will fallback this UART 
probe in irq mode.
Whatever the patch ordering, the boot will never be broken. The board dt 
patches aim to get a "proper" implementation, but from functional 
perspective the driver will manage a request to probe an UART console in 
DMA mode as an error and fall it back in irq mode.

Cheers, Erwan.

> > > 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(+)