[adding more people and MLs on Cc for further discussion]
On 04.04.2014 17:44, Inki Dae wrote:
2014-04-04 22:55 GMT+09:00 Tomasz Figa <t.figa@xxxxxxxxxxx>:
Hi Inki,
On 01.04.2014 14:37, Inki Dae wrote:
This patch adds super device support to bind sub drivers
using device tree.
For this, you should add a super device node to each machine dt files
like belows,
In case of using MIPI-DSI,
display-subsystem {
compatible = "samsung,exynos-display-subsystem";
ports = <&fimd>, <&dsi>;
};
In case of using DisplayPort,
display-subsystem {
compatible = "samsung,exynos-display-subsystem";
ports = <&fimd>, <&dp>;
};
In case of using Parallel panel,
display-subsystem {
compatible = "samsung,exynos-display-subsystem";
ports = <&fimd>;
};
And if you don't add connector device node to ports property,
default parallel panel driver, exynos_drm_dpi module, will be used.
ports property can have the following device nodes,
fimd, mixer, Image Enhancer, MIPI-DSI, eDP, LVDS Bridge, or HDMI
With this patch, we can resolve the probing order issue without
some global lists. So this patch also removes the unnecessary lists and
stuff related to these lists.
I can see several problems with this approach:
1) It breaks compatibility with existing DT. After this patch it is no
longer possible to use old device trees and get a working DRM. However, in
my opinion, this requirement can be relaxed if we make sure that any users
are properly converted.
2) What happens if in Kconfig you disable a driver for a component that is
I'm not sure what you meant but there wouldn't be no way that users
*cannot disable* the driver for a component. The driver would be
exynos_drm_drv, not separated module, and would always be built as
long as users want to use *exynos drm driver*.
I think you don't understand what I mean. Let me show you an example:
You have a board with a DSI panel and also a HDMI output. So you have a
supernode pointing to FIMD, DSI and HDMI.
Now, an user finds that he doesn't need HDMI in his system, so he turns
off CONFIG_DRM_EXYNOS_HDMI. The supernode still points at hdmi node and
Exynos DRM core will register it as a component, but HDMI driver is not
available and will never probe, leading the whole Exynos DRM to never
initialize. Is this a desired behavior?
listed in supernode? If I'm reading the code correctly, Exynos DRM will not
And the only case a component isn't added to the list is when users
disabled sub driver.
See above.
The code creating the list of components to wait for
(exynos_drm_add_components()) doesn't seem to consider which sub-drivers
are actually enabled in kernel config.
register, which is completely wrong. Users should be able to select which
drivers should be compiled into their kernels.
So users are be able to select drivers they want to use, and will be
compiled correctly. So no, the only thing users can disable is each
sub driver, not core module.
3) Such approach leads to complete integration of all Exynos DRM drivers,
without possibility of loading some sub-drivers as modules. I know that
current driver design doesn't support it either, but if this series is
No, current drm driver *must also be built* as one integrated single
drm driver without super device approach.
As I wrote, I know that current design before this patch isn't modular
either, but this is not my concern here. See below.
So the super device approach
*has no any effect on existing design*, and what the super device
approch tries to do is to resolve the probe order issue to sub drivers
*without some codes specific to Exynos drm*.
My concern is that the supernode design is actually carving such broken
non-modular design in stone. Remember that we are currently heading
towards a fully multi-platform kernel where it is critical for such
subsystems to be modular, because the same zImage is going to be running
on completely different machines.
claimed to improve things, it should really do so.
4) Exactly the same can be achieved without changing the DT bindings at all.
In fact even without adding any new single property or node to DT. We
discussed this with Andrzej and Marek today and came to a solution in which
just by adding a little bit of code to Exynos DRM subdrivers, you could
guarantee correct registration of Exynos DRM platform and also get rid of
#ifdeffery in exynos_drm_drv.c. Andrzej will send an RFC after the weekend.
I'm not sure but I had implemented below prototype codes for that, see
the below link,
https://git.kernel.org/cgit/linux/kernel/git/daeinki/drm-exynos.git/commit/?h=exynos-bridge-test&id=2860ad02d736e300034ddeabce3da92614922b4e
I guess what you said would be similler approach.
Not exactly. The approach we found does mostly the same as componentized
subsystem framework but without _any_ extra data in Device Tree. Just
based on the list of subsystem sub-drivers that is already available to
the master driver.
And I still think the use of the component framework would be the best
solution and *Linux generic way* for resolving the probe order issue
without any specific codes. So I'm not advocating the compoent
framework but I tend not to want to use specific codes.
I understand your concern. I also believe that generic frameworks should
be reused wherever possible. However the componentized subsystem
framework is a bit of overkill for this simple problem. Moreover, Device
Tree is not a trash can where any data that can be thought of can be
thrown as you go, but rather a hardware description that is supposed to
be a stable ABI and needs to be well-thought. So, if something can be
done in a way that doesn't require additional data, it's better to do it
that way.
5) This series seems to break DPI display support with runtime PM enabled.
Universal C210 just hangs on second FIMD probe, after first one fails with
probe deferral. This needs more investigation, though.
For -next, I never expect that pm operations would be operated
perfactly. They are really not for product. Just adding new feature
and drivers to -next, and then fixing them while in RC. And RC process
would also be for it. Actually, I see pm interfaces of exynos_drm_dsi
driver leads to break a single driver model because pm operations
should be done at top level of exynos drm, and some codes Sean didn't
fix. So such things are in my fix-todo-list. I tend to accept new
features and drivers for -next as long as they have no big problem,
And that is my style I maintain.
Unless it breaks so much that the system is unable to boot at all, which
is the case. As I said, the system just hangs, like something would
access hardware that is not properly initialized, e.g. without power
domain or clocks enabled.
Anyway, I don't agree that regressions are allowed in linux-next,
especially if found before applying a patch. Linux-next is a tree in
which patches that are supposed to be ready to be pulled by Linus should
be pushed. Of course nobody can spot all the regressions before the
patches hitting -next and that's fine, as -next is an integration
_testing_ tree. However even if already in -next, regressions should be
fixed ASAP to minimize the number of fix patches needed during -rc period.
Best regards,
Tomasz
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