Re: [PATCH v2 13/18] ARM: dts: s6e3fa0: add DT bindings

[YoungJun Cho <yj44.cho@samsung.com>]

Hi ALL,

On 05/28/2014 03:44 PM, Andrzej Hajda wrote:
> On 05/28/2014 06:50 AM, Inki Dae wrote:
>> On 2014년 05월 28일 05:21, Thierry Reding wrote:
>>> On Tue, May 27, 2014 at 11:24:49PM +0900, Inki Dae wrote:
>>>> 2014-05-27 16:53 GMT+09:00 Thierry Reding <thierry.reding@gmail.com>:
>>>>> On Tue, May 27, 2014 at 08:28:52AM +0200, Andrzej Hajda wrote:
>>>>>> Hi Thierry,
>>>>>>
>>>>>> On 05/26/2014 03:41 PM, Thierry Reding wrote:
>>>>>>> On Wed, May 21, 2014 at 01:43:05PM +0900, YoungJun Cho wrote:
>>>>>>>> This patch adds DT bindings for s6e3fa0 panel.
>>>>>>>> The bindings describes panel resources, display timings and cpu mode timings.
>>>>>>>>
>>>>>>>> Signed-off-by: YoungJun Cho <yj44.cho@samsung.com>
>>>>>>>> Acked-by: Inki Dae <inki.dae@samsung.com>
>>>>>>>> Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
>>>>>>>> ---
>>>>>>>>   .../devicetree/bindings/panel/samsung,s6e3fa0.txt  |   45 ++++++++++++++++++++
>>>>>>>>   1 file changed, 45 insertions(+)
>>>>>>>>   create mode 100644 Documentation/devicetree/bindings/panel/samsung,s6e3fa0.txt
>>>>>>> You're totally confusing me here. Half of this patch series is about
>>>>>>> adding i80 support to Exynos FIMD, and then you go and add what is
>>>>>>> apparently a DSI peripheral driver here that's supposed to be used by
>>>>>>> this new i80 support. Nothing I've been able to dig up indicates that
>>>>>>> i80 or DSI are in anyway related.
>>>>>> FIMD can produce parallel RGB output or command mode in i80 style output
>>>>>> via parallel lines.
>>>>>> DSIM can accept parallel RGB stream in this case it produces MIPI DSI
>>>>>> video mode signal or it can accept i80 and in this case it translates it
>>>>>> to MIPI DSI command mode.
>>>>> Then the command mode timings aren't a property of the panel at all.
>>>> Then the video mode timings aren't also a property of the panel.
>>>>
>>>> Which interface mipi and display controller should use would be
>>>> decided by lcd panel type: display controller can use i80 interface
>>>> based lcd panel, and also mipi controller can use i80 interface based
>>>> lcd panel.
>>>> In here, the only difference is that lcd panel receives  packets,
>>>> which includes video data or command data, packed with mipi protocol
>>>> via lane lines or receives video data or command data via parallel
>>>> lines.
>>>>
>>>> And the below is LCD types,
>>>>          RGB interface panel.
>>>>          i80 interface panel.
>>>>          MIPI based RGB interface panel.
>>>>          MIPI based i80 interface panel.
>>>>
>>>> RGB interface also is called video mode, and i80 interface also is
>>>> called cpu mode. In case of omap SoC, it is also called Smart panel.
>>>> i80 interface is just one of LCD types. So I think this interface
>>>> timings should be handled by frameworks related to mode in same way as
>>>> RGB interface.
>
> Some clarification about names.
> I am not an expert in command/cpu mode interface, so feel free to
> correct me.
> Those different terms were quite confusing for me so after some digging
> (for example here [1])
> I have found/ensured  there is a following relation between different names:
> MIPI DPI - RGB interface
> MIPI DBI type A - CPU mode m68 style
> MIPI DBI type B - CPU mode i80 style
> MIPI DBI type C - SPI, maybe also other serial interfaces (?)
> MIPI DSI - based on D-PHY-s serial protocol which can work in video or
> command mode.
>
> To add more confusion CPU mode is also named MPU mode or sys mode.
>
> To avoid confusion in the discussion I propose use i80 only to describe
> DBI type B interface,
> and DSI command mode, DSI video mode to describe DSI modes.
>
> [1]: http://www.allshore.com/pdf/DA8620.pdf
>
>
>>> LCD is a display technology, it has nothing to do with the interface. My
>>> point is that from Andrzej's description, and in fact from this patch
>>> series in general, the S6E3FA0 panel is a DSI panel. Associating timings
>>> that are i80 specific to it is therefore wrong.
>>>
>>> Consider for instance what would happen if somebody were to use the same
>>> panel on some other device (connected to a DSI controller). If you
>>> specify i80 timings for the panel then the new device won't know what to
>>> do with them because it expects DSI-related timings.
>>>
>>> Let me try to summarize the above to make sure we're all on the same
>>> page:
>>>
>>> 	- FIMD is a display controller that can be configured to either
>>> 	  send RGB data or i80 data
>>> 	- DSIM takes either RGB as input and outputs DSI (video mode) or
>>> 	  i80 as input and outputs DSI (command mode)
>>>
>>> In both cases the panel is connected to DSIM and it takes DSI as input,
>>> because it is a DSI panel (it doesn't understand RGB or i80). The panel
>>> needs to describe the properties of the DSI interface so that DSIM can
>>> be configured appropriately. DSIM in turn works as a bridge or encoder
>>> that converts RGB or i80 to DSI (video or command mode). So it makes no
>>> sense to describe the i80 timings for the panel because it has nothing
>>> to do with i80. Instead the DSIM is the hardware that needs to specify
>>> the i80 timings, so that FIMD can be configured to generate the timings
>>> that DSIM needs.
>>              CPU interface                     MIPI lane
>> FIMD ----------------------- DSIM --------------------- LCD Panel
>>
>> Hmm... reasonable. So your point is that command mode timing should be
>> placed in fimd device node, not panel device node? And panel device node
>> should provide only a property that DSIM driver can set LCD mode
>> properly to i80 or rgb interface mode, and also FIMD driver can set LCD
>> mode to i80 or rgb interface mode.
>
> I have no access to s6e3fa0 datasheet and Exynos datasheet I have access to
> is not very verbose on the subject but it seems to be reasonable that
> cs-setup, wr-setup, wr-active and wr-hold are properties only of i80
> interface,
> ie interface between FIMD and DSIM and they have nothing to do with DSI
> command mode panel.
> Those properties should be provided by DSIM to FIMD, I guess they can be
> even hardcoded
> in DSIM driver, no bindings required. There is still a question how DSIM
> should tell FIMD about them.
> I am not sure about mechanism of passing them from DSIM to FIMD, maybe
> adjusting drm_display_mode
> is a solution, maybe different way of communication should be used (I
> see here again interface_tracker use case [2]).
>
> [2]:
> http://permalink.gmane.org/gmane.linux.drivers.video-input-infrastructure/77451
>
> On the other side width, height and clock are properties of the panel so
> they should stay
> with the panel, maybe width and height could be moved from dts to
> driver, I am not sure about frequency.
>
>>
>> Is there my missing point?
>>
>> And in case of Exynos, now video timing property is also placed in panel
>> device node so it needs to move to fimd device node.
>
> No, video timings are properties of panels so they should stay in
> panels, display
> controllers should just ask panels about them.
>
>>
>> Andrzej, do you have other opinion? I have looked into dts files for
>> other SoC and In most SoC, it seems that display controller node has
>> video timing property, not panel node. Thierry's pointing seems
>> reasonable to me.
> I guess there could be many reasons: historical, backward compatibility,
> laziness of developers :).
> I agree with Thierry also.
>
> So if everybody agrees there is only one serious issue: how the i80
> properties
> should be passed from DSIM to FIMD, am I right?

Right, this issue was difficult for me.
So in my first RFC v1, I placed them in FIMD dts[1].
I didn't think of that(placed them in DSIM), moved them to panel.

[1] : http://www.spinics.net/lists/dri-devel/msg57960.html

And do you think that it is also required to rename cmdmode to i80mode?

Thank you.
Best regards YJ

>
> Regards
> Andrzej
>
>>
>> Thanks,
>> Inki Dae
>>
>>> Thierry
>>>
>>
>
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