How to create a drm_display_mode for a new display

How to create a drm_display_mode for a new display

[Bas Vermeulen]

Hello,

I am trying to create a new display mode for a new display I have to 
support.

I have the following information:

Dotclock - frequency period - 1/TCLP - 89.6 MHz
                               TCDP - 11,16 ns

Hsync - Period - TH - 2048 dotclock, 43,75 KHz, 22,86 us
         Pulse Width - THp - 40 dotclock, 0,45 us - active low, sync 
pulse high, polarity+

Vsync - Period - TV - 729 dotclock, 60 Hz, 16,66 ms
         Pulse Width - TVp - 2 line, 45,72 us - active low, sync pulse 
high, polarity+

Enable - Pulse Width - THd - 1920 dotclock

V Display - Term - TVd - 720 line
             Start - TFd - 5 line

Phase - Hsync-Enable - THe - 88 dotclock
         Hsync-Vsync - TVh - 0 dotclock

I made the following drm_display_mode out of it:

{ DRM_MODE("1920x720", DRM_MODE_TYPE_DRIVER, 89600, 1920, 1920,
          1960, 2048, 0, 720, 722, 724, 729, 0,
          DRM_MODE_FLAG_NHSYNC | DRM_MODE_FLAG_NVSYNC),
          .vrefresh = 60, .picture_aspect_ratio = 
HDMI_PICTURE_ASPECT_16_9, },

Am I interpreting the specifications correctly? The display is unable to 
handle the signal I am currently sending, so something is wrong.

Bas Vermeulen


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Re: How to create a drm_display_mode for a new display

[Ville Syrjälä]

On Tue, Nov 12, 2019 at 03:18:21PM +0100, Bas Vermeulen wrote:
> Hello,
> 
> I am trying to create a new display mode for a new display I have to 
> support.
> 
> I have the following information:
> 
> Dotclock - frequency period - 1/TCLP - 89.6 MHz
>                                TCDP - 11,16 ns
> 
> Hsync - Period - TH - 2048 dotclock, 43,75 KHz, 22,86 us
>          Pulse Width - THp - 40 dotclock, 0,45 us - active low, sync 
> pulse high, polarity+
> 
> Vsync - Period - TV - 729 dotclock, 60 Hz, 16,66 ms
>          Pulse Width - TVp - 2 line, 45,72 us - active low, sync pulse 
> high, polarity+
> 
> Enable - Pulse Width - THd - 1920 dotclock
> 
> V Display - Term - TVd - 720 line
>              Start - TFd - 5 line
> 
> Phase - Hsync-Enable - THe - 88 dotclock
>          Hsync-Vsync - TVh - 0 dotclock

You don't happen to have an actual timing diagram to go along with
those?

> 
> I made the following drm_display_mode out of it:
> 
> { DRM_MODE("1920x720", DRM_MODE_TYPE_DRIVER, 89600, 1920, 1920,
>           1960, 2048, 0, 720, 722, 724, 729, 0,

The zero length horizontal front porch is perhaps a bit odd,
but looks like it could be correct given THp==40 and THe==88.

Also not sure about the the vertical front vs. back porch.
Maybe try swapping those around?

>           DRM_MODE_FLAG_NHSYNC | DRM_MODE_FLAG_NVSYNC),

Not sure those are correct. It does says "active low" but then it has
that "sync pulse high, polarity+" stuff as well. Confusing. Could
be worth a shot to try flipping these.

-- 
Ville Syrjälä
Intel
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Re: How to create a drm_display_mode for a new display

[Bas Vermeulen]

On 12-11-19 16:08, Ville Syrjälä wrote:
> On Tue, Nov 12, 2019 at 03:18:21PM +0100, Bas Vermeulen wrote:
>> Hello,
>>
>> I am trying to create a new display mode for a new display I have to
>> support.
>>
>> I have the following information:
>>
>> Dotclock - frequency period - 1/TCLP - 89.6 MHz
>>                                 TCDP - 11,16 ns
>>
>> Hsync - Period - TH - 2048 dotclock, 43,75 KHz, 22,86 us
>>           Pulse Width - THp - 40 dotclock, 0,45 us - active low, sync
>> pulse high, polarity+
>>
>> Vsync - Period - TV - 729 dotclock, 60 Hz, 16,66 ms
>>           Pulse Width - TVp - 2 line, 45,72 us - active low, sync pulse
>> high, polarity+
>>
>> Enable - Pulse Width - THd - 1920 dotclock
>>
>> V Display - Term - TVd - 720 line
>>               Start - TFd - 5 line
>>
>> Phase - Hsync-Enable - THe - 88 dotclock
>>           Hsync-Vsync - TVh - 0 dotclock
> You don't happen to have an actual timing diagram to go along with
> those?


Unfortunately I don't. I'm currently trying to get it.


>> I made the following drm_display_mode out of it:
>>
>> { DRM_MODE("1920x720", DRM_MODE_TYPE_DRIVER, 89600, 1920, 1920,
>>            1960, 2048, 0, 720, 722, 724, 729, 0,
> The zero length horizontal front porch is perhaps a bit odd,
> but looks like it could be correct given THp==40 and THe==88.
>
> Also not sure about the the vertical front vs. back porch.
> Maybe try swapping those around?

Thanks for the hint, I'll try that.

>>            DRM_MODE_FLAG_NHSYNC | DRM_MODE_FLAG_NVSYNC),
> Not sure those are correct. It does says "active low" but then it has
> that "sync pulse high, polarity+" stuff as well. Confusing. Could
> be worth a shot to try flipping these.

I'll try flipping those as well, thanks.

Bas Vermeulen


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