Hi Rob,

On Wed, 18 Oct 2017 08:29:07 -0500
Rob Herring [off-list ref] wrote:

On Wed, Oct 18, 2017 at 1:25 AM, Miquel RAYNAL
[off-list ref] wrote:

quoted

Hi Rob,

On Tue, 17 Oct 2017 17:00:22 -0500
Rob Herring [off-list ref] wrote:
 

quoted

On Fri, Oct 13, 2017 at 11:01:45AM +0200, Miquel Raynal wrote:  

quoted

Update the Device Tree binding documentation for the Marvell EBU
UART, in order to allow describing the extended UART IP block, in
addition to the already supported standard UART IP. This requires
adding a new compatible string, the introduction of a clocks
property, and extensions to the interrupts property.

Signed-off-by: Miquel Raynal <redacted>
Reviewed-by: Gregory CLEMENT <redacted>
---
 .../devicetree/bindings/serial/mvebu-uart.txt      | 49
+++++++++++++++++++--- 1 file changed, 44 insertions(+), 5
deletions(-)

diff --git
a/Documentation/devicetree/bindings/serial/mvebu-uart.txt
b/Documentation/devicetree/bindings/serial/mvebu-uart.txt index
d37fabe17bd1..3df3a3fab4bb 100644 ---
a/Documentation/devicetree/bindings/serial/mvebu-uart.txt +++
b/Documentation/devicetree/bindings/serial/mvebu-uart.txt @@
-1,13 +1,52 @@ -* Marvell UART : Non standard UART used in some
of Marvell EBU SoCs (e.g., Armada-3700) +* Marvell UART : Non
standard UART used in some of Marvell EBU SoCs
+                 e.g., Armada-3700.

 Required properties:
-- compatible: "marvell,armada-3700-uart"
+- compatible:
+    - "marvell,armada-3700-uart" for the standard variant of the
UART
+      (32 bytes FIFO, no DMA, level interrupts, 8-bit access to
the
+      FIFO, baudrate limited to 230400).
+    - "marvell,armada-3700-uart-ext" for the extended variant of
the
+      UART (128 bytes FIFO, DMA, front interrupts, 8-bit or
32-bit
+      accesses to the FIFO, baudrate unlimited by the
dividers).  

What do you call the next extended version?
marvell,armada-3700-uart-ext-ext?  

I don't know what you mean by "next extended version"?  

IP evolves on new chips with new features. Just trying to understand
how you are

I think I misunderstood your initial question.

Indeed you are right, I did not think about the naming of a potential
next extended version of the extended IP, but I don't know how to
rename it otherwise than "-ext" to best fit what the "new" IP
does.

quoted

quoted

This is different versions of UART on the same chip?  

Today in mainline there is support for the A3700 UART IP.
This series add support for another IP, based on the A3700, but with
extended features (explaining the -ext suffix).

Can you precise what is bothering you?  

Is this different versions of UART IP on 1 chip or a new version of
the UART IP on a new SoC? The latter should be a new compatible with
the new SoC. The former case does happen some, but is not common. I'm
just trying to understand which applies here.

Actually, both IP are available since the first version of the
Armada 3700 SoCs. There is no other implementation of these IPs yet. I
think we fall in the former case.

quoted

quoted

quoted

 - reg: offset and length of the register set for the device.
-- interrupts: device interrupt
+- clocks: UART reference clock used to derive the baudrate (only
+      mandatory with "marvell,armada-3700-uart-ext"
compatible).  

How is this optional? The freq is fixed if not present? If so, what
frequency?  

The "clocks" property should not be optional at all but that is how
the bindings were handled before this series, so I can't tell now
that this property is mandatory as it would break compatibility
with older versions of the driver.  

Okay. I think it should be mandatory with a note how missing property
is handled.

Sure.

quoted

When no clock is provided, the frequency is fixed by the bootloader
and cannot be changed. There is no standard frequency for it but the
one chosen by the bootloader often is 115200 as the UART is usually
used as the serial console.

Because the bootloader does only initialize the UART in use for the
serial console, the clock is mandatory when using another port or it
will not work at all.  

Thank you,
Miqu?l


-- 
Miquel Raynal, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com