linux-kernel - Re: [PATCH v7 3/4] drm/panel: Add support for S6E3HA2 panel driver on TM2 board

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Message-id: <aeab26bc-76a8-0b4d-b5b9-b8602fcf2eb3@samsung.com>
Date:   Mon, 09 Jan 2017 10:53:53 +0100
From:   Andrzej Hajda <a.hajda@...sung.com>
To:     Inki Dae <inki.dae@...sung.com>,
        Andi Shyti <andi.shyti@...sung.com>
Cc:     Hoegeun Kwon <hoegeun.kwon@...sung.com>, robh@...nel.org,
        thierry.reding@...il.com, airlied@...ux.ie, kgene@...nel.org,
        krzk@...nel.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-samsung-soc@...r.kernel.org, cw00.choi@...sung.com,
        jh80.chung@...sung.com, Donghwa Lee <dh09.lee@...sung.com>,
        Hyungwon Hwang <human.hwang@...sung.com>
Subject: Re: [PATCH v7 3/4] drm/panel: Add support for S6E3HA2 panel driver on
 TM2 board

On 09.01.2017 10:19, Inki Dae wrote:
>
> 2017년 01월 09일 16:37에 Andrzej Hajda 이(가) 쓴 글:
>> On 06.01.2017 09:36, Inki Dae wrote:
>>> 2017년 01월 06일 17:18에 Andi Shyti 이(가) 쓴 글:
>>>> Hi Inki,
>>>>
>>>> Thanks for the reply, but...
>>>>
>>>>>>> +static const struct drm_display_mode default_mode = {
>>>>>>> +	.clock = 222372,
>>>>>>> +	.hdisplay = 1440,
>>>>>>> +	.hsync_start = 1440 + 1,
>>>>>>> +	.hsync_end = 1440 + 1 + 1,
>>>>>>> +	.htotal = 1440 + 1 + 1 + 1,
>>>>>>> +	.vdisplay = 2560,
>>>>>>> +	.vsync_start = 2560 + 1,
>>>>>>> +	.vsync_end = 2560 + 1 + 1,
>>>>>>> +	.vtotal = 2560 + 1 + 1 + 15,
>>>>>>> +	.vrefresh = 60,
>>>>>>> +	.flags = 0,
>>>>>>> +};
>>>>>> how is this working with tm2e? Are these values valid for both
>>>>>> the boards?
>>>>> We don't need to consider tm2e board with two reasones,
>>>>> 1. there is no tm2e board support in mainline
>>>>> 2. the panel on tm2 would be a little bit different from one on tm2e
>>>> ... this display in the Tizen Kernel is supported by both:
>>>> tm2 [1] and tm2e [2]. The only differences are:
>>> Why tm2e dts file is in mainline? Seems communication miss with Chanwoo. :( 
>>>
>>>> TM2:
>>>>    clock-frequency = <14874444>;
>>>>    hactive = <1440>;
>>>>
>>>> TM2E:
>>>>    clock-frequency = <16523724>;
>>>>    hactive = <1600>;
>>>>
>>>> I don't know much about the differences you mention in point 2,
>>>> but it's a pity to drop support only because we don't want to put
>>>> in the dts the 'hactive', and 'clock-frequency' properties.
>>> Anyway, tm2e board is already in mainline so Panel driver may need to identify what kinds of panel is probed to decide porch values. I think there are relevant registers in MCU of the Panel device to check version or similar thing.
>> I think we can safely use different compatible string for tm2e - it uses
>> different display IC controller - s6e3hf2, driver will provide timings
>> based on it.
> Using compatable string wouldn't be a good idea because Panel is a device not specific to board.

But both panels are different devices:
TM2 has: AMS567DJ01 panel on S6E3HA2 interface (called LDI/IC)
TM2E has AMB559DE01 panel on S6E3HF2 interface (called LDI/IC)

Why assigning different compatibles to different devices is not a good idea?

>
>> As far as I examined available specs/docs there is no reliable register
>> which can be used to safely distinguish it on runtime, but the docs I
>> have are far from completeness.
> The data sheet I am seeing says a RDDIDS register describes manufacturer and module version information. With this we could identify the Panel device.
> Of course, we may need to check the register has really different values according to board.
>
> Below is the version information Hoegeun checked,
>
> TM2
> [    4.908666] panel_s6e3ha2 13900000.dsi.0: Manufacture date: 2014-10-31 06:41
> [    5.035768] panel_s6e3ha2 13900000.dsi.0: Id: 50 20 09
>
> TM2e
> [    4.929265] panel_s6e3ha2 13900000.dsi.0: Manufacture date: 2014-09-03 06:30
> [    5.056287] panel_s6e3ha2 13900000.dsi.0: Id: 40 40 14

There is description of ID1, ID2, ID3 registers in specs of both panels,
I see no reliable bits to distinguish panels.
And relying on read values of random devices does not seems to me proper
solution.

Regards
Andrzej


>
>
> Thanks.
>
>> Regards
>> Andrzej
>>
>>> Thanks.
>>>
>>>> Andi
>>>>
>>>> [1] https://git.tizen.org/cgit/platform/kernel/linux-exynos/tree/arch/arm64/boot/dts/exynos/exynos5433-tm2.dts?h=tizen#n1284
>>>> [2] https://git.tizen.org/cgit/platform/kernel/linux-exynos/tree/arch/arm64/boot/dts/exynos/exynos5433-tm2e.dts?h=tizen#n1270
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>>>>
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>