On 10/23/2013 07:52 PM, Jani Nikula wrote:
On Wed, 23 Oct 2013, Shobhit Kumar <shobhit.kumar@xxxxxxxxx> wrote:
Hi Jani,
On 10/22/2013 05:23 PM, Jani Nikula wrote:
On Tue, 22 Oct 2013, Shobhit Kumar <shobhit.kumar@xxxxxxxxx> wrote:
On 10/21/2013 6:57 PM, Jani Nikula wrote:
Hi Shobhit -
On Mon, 21 Oct 2013, Shobhit Kumar <shobhit.kumar@xxxxxxxxx> wrote:
Also add new fields in intel_dsi to have all dphy related parameters.
These will be useful even when we go for pure generic MIPI design
I feel like we have a different idea of what the ideal generic design
is. For me, the goal is that we change the struct intel_dsi_device to
struct drm_bridge, and those drm_bridge drivers are all about the panel,
and have as few details about i915 or our hardware as possible. Having
the bridge drivers fill in register values to be written by the core DSI
code does not fit that. Yes, I had some of those in my bridge conversion
patches too, but I did not intend we'd keep adding more.
I'd rather we provide generic helpers the bridge driver can call.
Yeah, look like our ideas are different. In your goal with drm_bridge
architecture, we will still end up having multiple bridge drivers for
each different panel. But my goal is to have a single driver which can
work for multiple panels.
I'm trying to look one or two steps further, and what it will mean to
the driver. Here's the long term goal in upstream as I see it: There
will be a framework in place that allows one to write a (DSI) panel
driver once, using generic APIs, and use that panel driver with any SoC
(that implements the other side of the framework).
To clarify in terms of what we have currently, in my opinion intel_dsi.c
is one such SoC specific implementation for BYT and associated MIPI host
controller. And sub-encoder drivers are other end and I want to unify
sub-encoder side to have just one sub-encoder for any panel out there.
What you are talking makes perfect sense if we are going to have each
panel driver as a separate driver. But we can still achieve this
separation with common panel driver as well.
We are obviously far away from that goal at the moment. But IMHO we
should keep that in mind as a guide to what we are doing now. Moving
towards a model with a clearly defined API between the DSI core and the
panels, where the panel specific things are abstracted away from the
core, or towards a model where the core and panel driver depend on the
implementation of each other, communicating via variables.
I think we are aligned on the goal and I feel there is a need for common
DSI core to be separate
Since we already have enabled some panels with sub-encoder
architecture for completeness I was planning to maintain generic
driver as one sub-encoder.
Nothing prevents you from doing that, as long as the separation between
the core and the panel drivers remains clear.
But actually we can do away with all sub-encoder and do not need even
drm_bridge and all implementation will be in intel_dsi.c. Panel
specific configurations or sequences will come from VBT which I have
tried to convert as parameters.
With this model it is all too easy to forget what is the panel driver
and what is the SoC driver. They *are* two separate things, and should
not be mixed. It will be all too easy to keep adding new parameters and
conditions in the code as new panel drivers appear to need them. It will
lead to code that is very difficult to understand and maintain.
I think here you have misunderstood my proposal. I still treat SoC
driver and actual Panel driver as separate. And whatever parameters I
have tried to add are all DSI/DPHY spec related. There is not even
single parameter which is panel specific. If you are confusing this
because of use of -
if (intel_dsi->dsi_clock_freq)
dsi_clk = intel_dsi->dsi_clock_freq;
I feel it is okay to have this parameter which provides provision for
spec parameters to be hard-coded instead of calculating if a panel needs
and this is *only* such parameter and I already have ways to remove it
as well. IMHO it is a small price to pay to get one generic panel driver.
That is another thing if the DSI/DPHy specs themselves evolve and we
need to modify our core, but that is unavoidable I guess.
A model similar to what I'm proposing has also been tried and tested,
with several panels: drivers/video/omap2/. It's not DRM, and the control
is in the panel drivers, but the separation is extremely clear (panel
drivers are separate kernel modules).
Understand, but again my idea is to have one single driver which can
work for all panels and hence there is no need of multiple panel
drivers. This works with SoC side of the framework. I have not yet
described how we can achieve this, but first does it has any merit to
have something like this ?
My educated guess is that a single panel driver is not going to work for
*all* panels, *but* it is of course benefitial to share each panel
driver for as many panels as technically makes sense.
So yes, I agree there's merit in having a panel driver that works on a
bunch of panels based on parameters from the VBT. Apologies if it
sounded like I'm against that.
Based on my (limited, but not insignificant) experience with DSI panels,
you can't parametrize everything, and you will need panel specific code
to handle them. I presume there will also be cases where we won't have
the parameters in VBT. The DSI specs do not cover everything, and some
panels are outright out of spec. And then there are DSI->LVDS bridges
etc. needing special attention.
In my understanding there are two things - one is configuration
parameters and the sencond is panel specific sequneces for say
enable/disable itself. To support both of them there is a design update
in VBT as such. So far as per our experience till now on whatever panels
we have enabled, we could cover them with common driver + VBT. But you
are right there might be some really quirky panels which might fall out
of this driver and that is why I am all for having sub-encoder design as
is today and bridge driver in near future and want to ensure that the
generic driver is as per the sub-encoder for now and drm_bridge soon.
Initially I was only aiming for native MIPI, but now I see some needs
for DSI->LVDS bridge also. So this is a good point to consider as well.
So I think let's keep trying to find the right abstractions to separate
the DSI core and the panel drivers, make it possible to support several
panels with one driver, and make it possible to have independent drivers
for panels that don't fit the assumptions of the generic panel driver.
Does that conflict with your goals? Are we in agreement here?
Definetely we are in agreement and perfectly aligns with my goals. But
is it okay to work towards pushing sub-encoder based design for
immidiate short term and then work to convert on drm_bridge because I
can see that drm_bridge callbacks will need additions defintely and it
might take some time to get that done. In the meantime can we push
current driver with already suggested changes to get atleast a working
base ?
No doubt the clear separation between the core and the panel drivers
will be harder and more work in the short term, but it will pay off in
the long term. And it doesn't all have to happen at once, as long as we
work *towards* that goal, not away from it.
I think we should take into account the amount of effort required to
develop and maintain bridge drivers for tens of MIPI panel out there Vs
having one panel driver to maintain and make fully spec compliant taking
care of open ends left by the specs in the best way we can to achieve
this generality.
See above. I'm not proposing you split it all out to separate
drivers. Again, I'm sorry if I haven't been clear about that.
Now, the question is how do we achieve all this. First things first,
let's try to get any straightforward changes merged (small patches!), so
we can at least narrow the gap to upstream. And I need to have a look at
your panel driver code.
Sure. And as I propsed above we can push smaller cleaner patches for
current design itself to get working base. Generic panel driver comes
after that.
Regards
Shobhit
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