techskies11
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Does DSI have better support

Fri Nov 17, 2017 12:05 am

I read in the forums that DSI is limited due to lack of GPU drivers.
How is the DSI situation now since the raspberry 3 is here

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DougieLawson
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Re: Does DSI have better support

Fri Nov 17, 2017 12:32 am

Nothing changes. The only DSI device that's currently supported is the official RPF 7" touch screen.
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techskies11
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Re: Does DSI have better support

Fri Nov 17, 2017 3:55 am

Well when people use screens in the GPIO how does it run, does it use GPU

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rpdom
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Re: Does DSI have better support

Fri Nov 17, 2017 5:07 am

That depends on the screen.

Most of the small screens that connect to GPIOs use the SPI bus. There are various drivers for those. None of them use the GPU. They often copy the framebuffer to the screen.

Some larger screens can use the DPI interface which uses almost all of the GPIOs to give an 18-bit RGB output. They will need to either have a suitable parallel interface (which may need level shifting or a simple driver board), or a more complex driver board. Also VGA screens can be connected vi this interface and Gert's VGA666 adaptor which uses resistors to convert the parallel RGB data to analogue VGA RGB signals.
The DPI interface is driven by the GPU.

techskies11
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Re: Does DSI have better support

Fri Nov 17, 2017 5:24 am

Oh ok then What is the average frame rate of the small screens

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rpdom
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Re: Does DSI have better support

Fri Nov 17, 2017 6:11 am

That would depend on the resolution and how clever the driver is.
(I've no idea, to be honest).

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Gavinmc42
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Re: Does DSI have better support

Fri Nov 17, 2017 7:06 am

DPI is supported via GPIO, faster than SPI , 50/60fps.
Some DSI stuff is coming, Eric Anholt has done a little on this recently.
So one day maybe more than just the one Pi display, which is well supported.
Next year?

A would say 320x240 SPI have good support.
DPI it pretty good and has high frame rate and 800x480, Hyperpixel etc.
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notro
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Re: Does DSI have better support

Fri Nov 17, 2017 9:43 am

DSI is supported by the vc4 driver and Eric is still backporting patches to rpi-4.9 even though it gets increasingly difficult, but we're heading for 4.14 now so that will better the vc4 backport situation.

I did a quick check to see if there are Linux supported DSI panels that we could try.
I found the drivers by looking at who calls mipi_dsi_attach(): http://elixir.free-electrons.com/linux/ ... dsi_attach

Everyone uses 4 lanes except:
2 lanes: drivers/gpu/drm/panel/panel-sharp-ls043t1le01.c
1 lane: drivers/gpu/drm/panel/panel-raspberrypi-touchscreen.c

AFAIU we have 2 lanes on the regular boards and 4 and the CM's.

Some SPI display performance numbers: https://github.com/notro/fbtft/wiki/Performance

techskies11
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Re: Does DSI have better support

Fri Nov 17, 2017 12:26 pm

Hmm I would just need a front lcd display on a case that has decent frame rate to display a audio sprectum in real time without lagging due to slow frame rates,

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Gavinmc42
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Re: Does DSI have better support

Fri Nov 17, 2017 3:35 pm

How big a display?
DPI should be fast enough but you lose the GPIO.
One thing I am looking at is Zero's for off loading extra displays.
4 x USB powered/connected Zero's per Pi3 :D :D
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techskies11
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Re: Does DSI have better support

Fri Nov 17, 2017 6:32 pm

Hmm interesting lol

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