[maemo-developers] Does anyone know the mechanism in Nokia's LCD driver?

[From: Huang Gao (Gmail)]

Hi, Frantisek:

       Thank you for your reply!

       But I am still wondering why the screen will not flicker if the DMA
only refreshes when the data changed. Does Nokia uses something like smart
panel?

 

Best Regards

Huang Gao(黄杲)

 

-----邮件原件-----
发件人: Frantisek Dufka [mailto:dufkaf at seznam.cz] 
发送时间: 2009年1月13日 16:56
收件人: Huang Gao (Gmail)
抄送: maemo-developers at maemo.org
主题: Re: Does anyone know the mechanism in Nokia's LCD driver?

 

Huang Gao (Gmail) wrote:

> Dear all Maemo fans:

> 

>        I just noticed that Maemo used a different mechanism in LCD 

> driver from normal FB drivers. It seemed that Maemo does not use the 

> automatic DMA refresh in the driver, which is replaced by an ioctl named 

> OMAPFB_UPDATE_WINDOW, and a method called TEARSYNC. However, I am 

> confused why it will improve the performance of graphics applications. 

> Is there anyone that may give me some tips on this topic?

 

This was done because of relatively high resolution (800x480x16 bits).

Automatic DMA would continuously steal a lot of SDRAM cycles and slowed

down everything. Perhaps it would also eat more power and prevented

system from sleep when the display is on.

 

I wonder if this is still the case for upcoming OMAP3 based device.

 

BTW, there is kernel ioctl to set automatic refresh and the refresh rate

can be tweaked in kernel source but the results are suboptimal. Maybe at

least for Nokia 770 it would be possible to use tearsync flag for such

automatic update and set the update timer to lcd refresh rate or lcd

refresh rate/2 to get nice result. N8x0 cannot update whole screen in

one lcd refresh cycle anyway so you'll always get tearing on the bottom.

 

Frantisek

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