On 11/09/2018 16:59:09+0200, Geert Uytterhoeven wrote:

Hi Alexandre,

On Tue, Sep 11, 2018 at 11:40 AM Alexandre Belloni
[off-list ref] wrote:

quoted

On 11/09/2018 10:33:56+0100, Lee Jones wrote:

quoted

On Tue, 04 Sep 2018, Radu Pirea wrote:

quoted

Radu Pirea (6):
  MAINTAINERS: add at91 usart mfd driver
  dt-bindings: add binding for atmel-usart in SPI mode
  mfd: at91-usart: added mfd driver for usart
  MAINTAINERS: add at91 usart spi driver
  spi: at91-usart: add driver for at91-usart as spi
  tty/serial: atmel: change the driver to work under at91-usart mfd

 .../bindings/{serial => mfd}/atmel-usart.txt  |  25 +-
 MAINTAINERS                                   |  16 +
 drivers/mfd/Kconfig                           |   9 +
 drivers/mfd/Makefile                          |   1 +
 drivers/mfd/at91-usart.c                      |  71 +++
 drivers/spi/Kconfig                           |   8 +
 drivers/spi/Makefile                          |   1 +
 drivers/spi/spi-at91-usart.c                  | 432 ++++++++++++++++++
 drivers/tty/serial/Kconfig                    |   1 +
 drivers/tty/serial/atmel_serial.c             |  42 +-
 include/dt-bindings/mfd/at91-usart.h          |  17 +
 11 files changed, 606 insertions(+), 17 deletions(-)
 rename Documentation/devicetree/bindings/{serial => mfd}/atmel-usart.txt (76%)
 create mode 100644 drivers/mfd/at91-usart.c
 create mode 100644 drivers/spi/spi-at91-usart.c
 create mode 100644 include/dt-bindings/mfd/at91-usart.h

Seeing as this patch-set has caused some issues this morning, I took
the liberty to peruse back into its history to figure out where things
started to go wrong.  I also re-reviewed the MFD driver - and I'm glad
I did!

My Acked-by has been attached to the MFD portion since v5, which is
why the code hasn't caught my eye before today.  I reviewed the
relocation of the *binding document* (serial => mfd with no changes)
in v4 and nothing else.  It appears as though you mistakenly added it
to the *MFD driver* instead.  This explains my confusion in v10 when I
told you I'd already reviewed the binding document.

As I said, I have re-reviewed the MFD driver and I'm afraid to say
that I do not like what I see.  Besides the missing header file and
the whitespace tabbing errors, I do not agree with the implementation.
Using MFD as a shim to hack around driver selection is not a valid
use-case.

What's stopping you from just using the compatible string directly to
select which driver you need to probe?

Then you'd have multiple compatible strings for the same IP which is a
big no-no.

It's still the same hardware device, isn't?
What if the SPI or UART slave is not on-board, but on an expansion board?
Then the SoC-specific .dtsi has no idea what mode should be used.

Hence shouldn't the software derive the hardware mode from the full
hardware description in DT? If that's impossible (I didn't look into detail
whether an SPI bus can easily be distinguished from a UART bus), perhaps
a mode property should be added?

Yes, this is exactly what is done:

https://git.kernel.org/pub/scm/linux/kernel/git/lee/mfd.git/tree/drivers/mfd/at91-usart.c?h=ib-mfd-spi-tty-4.20-1#n33

Only one compatbile for the IP and a property to know what is the mode.
That property should indeed be set in the board dts and not the SoC
dtsi.

the other, less robust alternative was to look for child nodes and
decide that if some where present it would indicate an SPI bus. But I
think at some point we may have child nodes under a UART node.

-- 
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com