On Tue, Dec 27, 2016 at 11:12:26AM +0100, Marek Szyprowski wrote:

Hi Tomasz,


On 2016-12-26 06:55, Tomasz Figa wrote:

quoted

2016-12-23 21:24 GMT+09:00 Marek Szyprowski [off-list ref]:

quoted

Pad retention control after suspend/resume cycle should be done from pin
controller driver instead of PMU (power management unit) driver to avoid
possible ordering and logical dependencies. Till now it worked fine only
because PMU driver registered its sys_ops after pin controller.

This patch moves pad retention control from PMU driver to Exynos pin
controller driver. This is a preparation for adding new features to Exynos
pin controller driver, like runtime power management and suspending
individual pin controllers, which might be a part of some power domain.

It looks like this change will essentially break the compatibility
with DTBs that don't have the pmu syscon specified in pin controller
nodes.

On the other hand, moving this code to where it actually belongs
really makes sense, so maybe we could just avoid the need of having
this property, by looking up the PMU manually, by hardcoded string or
so, if the proper property is not present?

Well, once again the topic of mythical device tree compatibility appearch.

There are imho following possibilities:

1. https://patchwork.kernel.org/patch/9477963/ ("Explicitly mark Samsung
   Exynos SoC bindings as unstable"), simply apply this approach and ignore
   users, who don't update their device tree blobs (are there any??).

That is not how it works. Assuming that there was this "mythical
compatibility" then you would have to wait a few moments between marking
something "to be broken" and actually breaking it. In other words, if
you wanted to silence the "breaking compatibility" folks, then the patch
above should have been sent a while ago.

2. Switch to syscon_regmap_lookup_by_compatible() lookup and hardcode PMU
   compatible id for all Exynos SoCs in the pin control driver. Then maybe,
   while unifying the code, switch other Exynos drivers to this approach
   and remove PMU phandles from device tree to make the code a bit more
   consistent across drivers and easier to understand.

3. Mixed approach, which combines drawbacks of both approaches. Additional
   dead code for handling mythical compatibility and harder to understand
   relations between the drivers.

quoted

[...]

quoted

diff --git a/Documentation/devicetree/bindings/pinctrl/samsung-pinctrl.txt b/Documentation/devicetree/bindings/pinctrl/samsung-pinctrl.txt
index 1baf19eecabf..b7bd2e12a269 100644
--- a/Documentation/devicetree/bindings/pinctrl/samsung-pinctrl.txt
+++ b/Documentation/devicetree/bindings/pinctrl/samsung-pinctrl.txt

@@ -43,6 +43,10 @@ Required Properties:
                 };
         };

+- samsung,pmu-syscon: Phandle to the PMU system controller, to let driver
+  to control pad retention after system suspend/resume cycle (only for Exynos
+  SoC series).
+

Ah, here it is. I think adding relevant binding documentation at the
beginning of the series would make it much easier for reviewers to
understand the change.

I already pointed that patches are ordered to make the changes bisectable,
what
usually means that new properties are added first, before being required by
the
drivers.

I saw the explanation for this order and I don't have problems with it.
However you can always split to separate patch the documentation for
bindings. It won't break bisectability.

Best regards,
Krzysztof