On 14.04.2014 15:55, Inki Dae wrote:
Hi Tomasz,
Always thanks for your opinions.
-----Original Message-----
From: linux-samsung-soc-owner@xxxxxxxxxxxxxxx [mailto:linux-samsung-soc-
owner@xxxxxxxxxxxxxxx] On Behalf Of Tomasz Figa
Sent: Monday, April 14, 2014 8:32 PM
To: Inki Dae; 'Andrzej Hajda'
Cc: 'Kyungmin Park'; 'moderated list:ARM/S5P EXYNOS AR...'; 'Russell
King';
dri-devel@xxxxxxxxxxxxxxxxxxxxx; 'Marek Szyprowski'
Subject: Re: [PATCH RFC 0/2] drm/exynos: refactoring drm device
init/deinit
Hi Inki,
On 14.04.2014 13:04, Inki Dae wrote:
-----Original Message-----
From: Andrzej Hajda [mailto:a.hajda@xxxxxxxxxxx]
Sent: Monday, April 14, 2014 5:55 PM
To: Inki Dae
Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx; moderated list:ARM/S5P EXYNOS
AR...; Kyungmin Park; Marek Szyprowski
Subject: Re: [PATCH RFC 0/2] drm/exynos: refactoring drm device
init/deinit
On 04/12/2014 04:18 PM, Inki Dae wrote:
Hi Andrzej,
Thanks for your contributions.
2014-04-11 23:11 GMT+09:00 Andrzej Hajda <a.hajda@xxxxxxxxxxx>:
Hi Inki,
This patchset refactors drm device initialization. Details are
described in respective patches. It is an alternative to DT
supernode
concept.
The first patch uses linker sections to get rid of ifdef macros, it
is not
That's a good idea. :) We could avoid ugly #ifdef ~ #endif with this
way.
essential for 2nd patch but it makes code more readable. Similar
approach is used by irqchip, clks and clk_sources.
But 2nd patch doesn't seem reasnoable to me. Your approach is same
as existing one conceptually. I think we need to handle drm driver
in a different way from irqchip, clks and clk_sources.
DRM driver means one integrated graphics card but in most embedded
systems, graphics and display relevant devices have separated
hardware resources. So we would need abstractional integrated
hardware, display-subsystem, super device. That is why I are trying
to use super device approach, and conceptually it would be right
solution. It wouldn't be not good to combine those separated
hardware somehow using specific codes.
Conceptually both approaches are the same: we have number of devices
which should be ready before we can start super-device and if any
device is to be removed super-device should be removed before.
The difference is in 'details':
- super-node approach have list of components provided explicitly in
DT special node,
- in this approach list of components is constructed from devices
present in the system.
Creating special DT node with information which is available anyway
seems to be redundant and against DT rules.
CCing Russell King,
What is the special DT node? You mean device node from ports property?
It is supposed to use super device and its properties in mainline so
I don't see what it is against DT rules. If they are really against DT
rules, why component framework is in mainline?
Component framework in mainline doesn't have anything in common with DT.
All it does is providing tools for handling cases where a subsystem can be
initialized only after all components are available. It doesn't define any
means of getting the list of components, it's a task for the user of this
framework to provide it.
As you said above, conceptually both approaches may be the same but
your approach has no any abstract hardware meaning one integrated
hardware. And if conceptually both approaches are the same, it would
be good to use existing infrastructure, component framework so there
is no any reason to add and use specific codes.
What do you mean by "abstract hardware"? Physically, in the SoC, there is
no single integrated hardware block, but multiple IPs and they need to be
described this way in DT. There is nothing that prevents using them
separately if a user doesn't want to use Exynos DRM. Exynos DRM is a
I don't think that super device approach prevents using existing device
nodes separately. If a user doesn't want to use Exynos DRM, he cannot
declare the super node and each IP would work well in existing way. There
would be nothing to change existing device nodes.
I agree that it wouldn't interfere with other possible use cases, but it
is still leaking Linux- and use case- specific data to DT, which should
be both OS and use case- agnostic. Especially when the goal to be
achieved doesn't even require doing so (see Andrzej's enumeration using
driver model objects directly).
Linux-specific thing and its details should not be leaked into DT, which
is a _hardware_ description method.
And component framework says,
"Subsystems such as ALSA, DRM and others require a single card-level
device structure to represent a subsystem. However, firmware tends to
describe the individual devices and the connections between them.
Therefore, we need a way to gather up the individual component devices
together, and indicate when we have all the component devices."
Note following things:
- Nothing in the quote above says that an additional DT node must be
added.
The framework works on generic driver model level, above the description
level (such as DT).
And also the component framework says,
"
We do this in DT by providing a "superdevice" node which specifies the
components, eg:
imx-drm {
compatible = "fsl,drm";
crtcs = <&ipu1>;
connectors = <&hdmi>;
};
"
So I think it is intended to use super device node and its property except
names specific to Linux, *drm, crtc, and connectors.
This is just an example, used by fsl DRM bindings, which is a bit
unfortunate IMHO, but maybe their case was more complex than Exynos DRM.
Note that core component framework code doesn't implement any DT
bindings, just expects the platform to provide the list of components.
- Andrzej's method implements the same concept as component framework,
except that:
a) it does so in a much more simple way (compare amount of code needed
for Andrzej's approach and inside component framework),
b) doesn't require component initialization to be undone on every
master bring-up failure,
c) uses the list of drivers known at compilation time to the Exynos DRM
subsystem to build the list of devices to wait for
d) doesn't introduce any new DT bindings, for virtual, Linux-specific
things,
e) doesn't duplicate compatible strings in an array used only to
support systems that didn't have nodes required by those new DT bindings
(as done in your exynos_drm_bind_lagacy_dt()),
f) doesn't require two-step initialization (probe() and bind()), as
opposed to component subsystem.
As you can see, it's a pure list of benefits, without any obvious
drawbacks, except that some generic code (more or less applicable here) is
not used.
However, I wonder whether some of Andrzej's ideas couldn't be simply
adopted by component framework (mostly b)) and Exynos DRM use of it (c),
d), e)) to take best of both worlds and have both a good implementation
and generic code reused.
Andrzej's method may be more clear than super device approach in some parts
but we have already a infrastructure for it.
So how about improving existing component framework if you think Andrzej's
method is same as super device approach, and is better than it? If do so, we
will use it naturally - no any reason not to use it.
I would be all for it.
I'm not against using the component framework at all - my primary
concern is adding the need for supernode in DT, while it is completely
unnecessary, as demonstrated by Andrzej's implementation.
Best regards,
Tomasz
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