[PATCH 1/2] dm: core: add support for fallback drivers

[Tom Rini]

On Wed, Apr 10, 2024 at 07:27:17PM +0200, Heinrich Schuchardt wrote:
> 
> 
> Am 10. April 2024 19:06:57 MESZ schrieb Caleb Connolly <caleb.connolly at linaro.org>:
> >Introduce support for a uclass to provide a fallback/stub driver which
> >can be used when no device is found for a given node. This might be
> >useful for handling non-essential clock controllers like the RPMh on
> >Qualcomm platforms, or during early bringup to get UART output before a
> >real clock driver has been created.
> >
> >Signed-off-by: Caleb Connolly <caleb.connolly at linaro.org>
> >---
> > drivers/core/Kconfig  | 10 ++++++++++
> > drivers/core/uclass.c | 24 +++++++++++++++++++++++-
> > include/dm/uclass.h   |  3 +++
> > 3 files changed, 36 insertions(+), 1 deletion(-)
> >
> >diff --git a/drivers/core/Kconfig b/drivers/core/Kconfig
> >index 1081d61fcf01..09075b9b7a15 100644
> >--- a/drivers/core/Kconfig
> >+++ b/drivers/core/Kconfig
> >@@ -466,5 +466,15 @@ config BOUNCE_BUFFER
> > 
> > 	  A second possible use of bounce buffers is their ability to
> > 	  provide aligned buffers for DMA operations.
> > 
> >+menuconfig FALLBACK_DRIVERS
> 
> Wouldn't it be preferable to mark individual drivers as fallback drivers in their declaration?
> 
> This would allow alternative fallback drivers and would not require any definitions at uclass level.
> 
> Just by building a fallback driver you would enable the fallback behavior for its uclass.

I think some of this is addressed in the cover letter. My concern /
questions come down to I think just a matter of naming. Both "fallback"
and "stub" are used at times. As a concept, we have some areas where we
need a no-op driver because whereas the DT describes a relationship in
the hardware, here in U-Boot we can just accept things as configured. To
me "fallback" implies more functionality of the driver when it's really
just a generic no-op driver to fill in the dependencies within the tree.
Can we rename things a bit along those lines?

-- 
Tom
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