Re: [PATCH v3 06/14] Documentation: drm/bridge: add document for analogix_dp

From: Yakir Yang
Date: Mon Aug 24 2015 - 21:34:26 EST

Hi Krzysztof,

å 2015/8/25 7:49, Krzysztof Kozlowski åé:
On 24.08.2015 21:48, Yakir Yang wrote:
Hi Krzysztof,

å 08/24/2015 12:20 PM, Krzysztof Kozlowski åé:
On 24.08.2015 11:42, Yakir Yang wrote:
Hi Krzysztof,

å 08/23/2015 07:43 PM, Krzysztof Kozlowski åé:
2015-08-24 8:23 GMT+09:00 Rob Herring <robherring2@xxxxxxxxx>:
On Wed, Aug 19, 2015 at 9:50 AM, Yakir Yang <ykk@xxxxxxxxxxxxxx>
Analogix dp driver is split from exynos dp driver, so we just
make an copy of exynos_dp.txt, and then simplify exynos_dp.txt

Beside update some exynos dtsi file with the latest change
according to the devicetree binding documents.
You can't just change the exynos bindings and break compatibility. Is
there some agreement with exynos folks to do this?
No, there is no agreement. This wasn't even sent to Exynos maintainers.
Sorry about this one, actually I have add Exynos maintainers in version
1 & version 2,
but lose some maintainers in version 3, I would fix it in bellow

Additionally the patchset did not look interesting to me because of
misleading subject - Documentation instead of "ARM: dts:".

Yakir, please:
1. Provide backward compatibility. Mark old properties as deprecated
but still support them.
Do you mean that I should keep the old properties declare in
but just mark them as deprecated flag.
That is one of ways how to do this. However more important is that
driver should still support old bindings so such code:
- if (of_property_read_u32(dp_node, "samsung,color-space",
+ if (of_property_read_u32(dp_node, "analogix,color-space",

is probably wrong. Will the driver support old DTB in the same way as it
was supporting before the change?
Okay, I got your means. So document is not the focus, the most important
is that
driver should support the old dts prop.
Right, the focus is on the driver.

If so the new analogix dp driver
should keep
the "samsung,color-space", rather then just mark it with [DEPRECATED] flag.
If you are replacing a binding/property then it should be marked
deprecated. This means that the old property is still working but new
users of it should not be added.

Okay, so just quote Heiko's reply, such code would be need in analogix dp driver.

if (of_property_read_u32(dp_node, "analogix,color-space",
if (of_property_read_u32(dp_node, "samsung,color-space",
&dp_video_config->color_space)) {

dev_err(dev, "failed to get color-space\n");
return ERR_PTR(-EINVAL);

But from your follow suggest, I think you agree to update driver code,
and just mark
old prop with deprecated flag. If so I think such code would not be wrong

- if (of_property_read_u32(dp_node, "samsung,color-space",
+ if (of_property_read_u32(dp_node, "analogix,color-space",
It looks wrong because it breaks backward compatibility with existing
DTB. As I said before:
1. Provide backward compatibility. Mark old properties
as deprecated but still support them.

And actually @Rob have suggest me to remove the prefix, just use
"color-space" here.
For new bindings I don't mind. But please remember about existing users,
existing DTB and bisectability.

Let me show same examples, make
me understand your suggest rightly.
exynos-dp already contains deprecated properties. Other ways of doing
this would be:

It depends up to you. The "touchscreen" looks good because it organizes
old properties in a common section. In case of exynos-dp.txt you can add
at beginning of file information about new bindings and mark everything
Whoops, thanks for your remind, I prefer the "touchscreen" style.

1. "samsung,ycbcr-coeff" is abandoned in latest analogix-dp driver,
I should not carry this to analogix-dp.txt document. But I should
keep this in
exynos-dp.txt document, and mark them with an little
"deprecated" flag.

Required properties for dp-controller:
-samsung,ycbcr-coeff (DEPRECATED):
YCbCr co-efficients for input video.

Is it right ?
Yes, this is right.

2. Separate all DTS changes to a separate patch, unless bisectability
would be hurt. Anyway you should prepare it in a such way that
separation would be possible without breaking bisectability.
So I should separate this patch into two parts, one is name "Document:",
the other is "ARM: dts: ".

Honestly, I don't understand what the "bisectability" means in this
I was referring to bisectability in general. The patchset should be
fully bisectable which means that it does not introduce any issues
during "git bisect". This effectively means that at each intermediate
step (after applying each patch, one by one) every existing stuff works
the same as previously without any regression. Including booting with
old DTB.
Oh, thanks for your careful explain, so I guess your first comment is
talking about
the "bisectability" that if I only apply the 01 - 05 patches, kernel
could not bootup
normally, cause driver need "analogix,color-space" but DTB only have
Right. In the same time please remember that kernel may be booted with
old DTB.

Okay, thanks a lot ;)

- Yakir

Best regards,

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