[PATCH v3] PWM: PXA: add device tree support to PWM driver

Dear Mike Dunn,

On 09/15/2013 07:07 AM, Marek Vasut wrote:

quoted

Dear Mike Dunn,

quoted

This patch adds device tree support to the PXA's PWM driver.  Only an OF
match table is added; nothing needs to be extracted from the device tree
node.  The existing ID table is reused for the match table data.

Tested on a Palm Treo 680 (both platform data and DT cases).

Signed-off-by: Mike Dunn <redacted>
---
Changle log:
v3:
- remove support for the polarity flag
- remove per-chip pwm index cell; define custom of_xlate()

   (now #pwm-cells = <1>)

- "compatible" strings for all devices added to OF match table
- various stylistic changes recommended by reviewers

v2:
- of_match_table contains only the "pxa250-pwm" compatible string;
require one device instance per pwm
- add Documentation/devicetree/bindings/pwm/pxa-pwm.txt
- add support for polarity flag in DT and implement set_polarity()
method

  (the treo 680 inverts the signal between pwm out and backlight)

- return -EINVAL instead of -ENODEV if platform data or DT node not
found - output dev_info string if platform data missing
- expanded CC list of patch

 Documentation/devicetree/bindings/pwm/pxa-pwm.txt | 31 ++++++++++++
 arch/arm/boot/dts/pxa27x.dtsi                     | 24 +++++++++
 drivers/pwm/pwm-pxa.c                             | 62

+++++++++++++++++++++++ 3 files changed, 117 insertions(+)

 create mode 100644 Documentation/devicetree/bindings/pwm/pxa-pwm.txt

diff --git a/Documentation/devicetree/bindings/pwm/pxa-pwm.txt

b/Documentation/devicetree/bindings/pwm/pxa-pwm.txt new file mode 100644
index 0000000..6fcf90c

--- /dev/null
+++ b/Documentation/devicetree/bindings/pwm/pxa-pwm.txt

@@ -0,0 +1,31 @@
+Marvell PWM controller
+
+Required properties:
+- compatible: should be one of:
+  - "marvell,pxa250-pwm"
+  - "marvell,pxa270-pwm"
+  - "marvell,pxa168-pwm"
+  - "marvell,pxa910-pwm"

This really is something I dont quite understand. Why should the driver
list _every_ _single_ existing CPU that contains such PWM block? Is
there any agreement about that? For me, it'd make much more sense to
list only the CPUs where the IP block actually changed in some way, so
that the differences can be discerned that way.

I believe that this was Stephen's suggestion.

I actually don't object myself.  For the price of a few strings, it
- clearly shows which SoCs the driver supports
- ensures that any future differences are handled cleanly (e.g., if a hw
bug in one is discovered and a work-around is implemented)
- keeps thngs clean if support for another processor which does have pwm hw
differences is added

Especially the third point... otherwise, you have the case of a somewhat
confusing many-to-one mapping of processors to compatible strings.

OK, to push it ad-absurdum, shall we not start listing every single revision of 
the CPU as well ? Like pxa250a0 250a1 etc ? Yes , this many-to-one mapping is 
something I don't quite understand, that's why I'd love to see a good reasoning 
from Stephen.

Best regards,
Marek Vasut