MPC5121e DIU driver - kernel crash writing alpha component

[Chen Hongjun-R66092]

Hi, 

Pls refer to my comment embedded. 

> -----Original Message-----
> From: 
> linuxppc-dev-bounces+hong-jun.chen=freescale.com at lists.ozlabs.
> org 
> [mailto:linuxppc-dev-bounces+hong-jun.chen=freescale.com at lists
> .ozlabs.org] On Behalf Of LD
> Sent: Friday, October 23, 2009 3:17 PM
> To: Linux ppc mailing list; Lucio Dona'
> Subject: MPC5121e DIU driver - kernel crash writing alpha component
> 
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> Hi all,
> I am working on Freescale MPC5121e evaluation board ADS512101 
> rev. 3 (M34K processor stepping), developing a graphical application.
> Just switched to ADS512101 rev. 4, 0M36P processor stepping.
> 
> I have problems with the video framebuffer driver, try to explain:
> 
> - - app is based on microwindows+fltk, framebuffer driver. On 
> rev3 board working ok.
> - - rev4 board: using the kernel from ltib 2009/06/02, just 
> adapted fsl-diu-fb.c and .h to support resolution and timings 
> of my lcd panel.
> 
> The board is booting ok (NFS), but my user space app keeps 
> crashing the kernel.
> 
> I noticed that in 0M36P processor stepping there are many 
> changes about the video interface (DIU), correcting some bugs 
> of the previous stepping ; seems that when I write to the ram 
> area which is mapped to Panel0 of the DIU the system randomly hangs.
> 
> After some debugging...
> 800x480, 32 bits per pixel, using plane1 (first plane, as 
> described in the processor's reference manual).
> If, from user space, I write some alpha component != 0 in 
> this plane then I have a complete system crash.
> The reference pdf says "There is no alpha component defined 
> for plane1 because there are no planes behind it."
> 

Sure, panel0 doesn't support alpha function, so you can't operate it.

> I did not yet investigate about writing in other planes ; 
> time is short...
> For now, patched microwindows driver for writing 0x00 in 
> alpha components, no more hangs.
> Reported to Freescale FAE, waiting for some answers.
> 
> Meanwhile: some suggestions about filtering alpha components 
> in the video driver ?

You can replace panel0 with panel1, which can support alpha function.

> I was thinking about some sort of double buffering : user space app
> (fltk--->microwindows) writes in a buffer, then the driver 
> clears alpha to 0x00 and memcpy to the real video buffer.
> 
> Problems:
> - - driver / user space sync. Vertical retrace ? ioctl ?
> - - waste of memory, needs double video buffers
> 
> 
> Any suggestions are welcome,
> work in progress.
> 
> Regards
> Lucio Dona'
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