linux-kernel - Re: UIO driver for framebuffer

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Message-ID: <20090628160021.GC3639@local>
Date:	Sun, 28 Jun 2009 18:00:21 +0200
From:	"Hans J. Koch" <hjk@...utronix.de>
To:	vijay baskar <cn.vijaibaskar@...tech.co.in>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: UIO driver for framebuffer

On Thu, Jun 25, 2009 at 05:11:25PM +0530, vijay baskar wrote:
> Hi all,
>
> I have written a uio driver for framebuffer device.

Why? Framebuffer devices should be handled by the framebuffer subsystem which
already makes the framebuffer accessible from userspace in a way that's
supported by many userspace libraries. Why do you want to reinvent the wheel
in an incompatible way?

> I added device  
> specific register memory in uio.mem. I also added DMA param memory in  
> uio.mem to perform DMA from userspace. Also video RAM  
> <http://fixunix.com/#> was mapped in kernel space using  
> dma_alloc_coherent() and a logical address was obtained. This logical  
> address was also added in uio.mem with memtype as UIO_MEM_LOGICAL  
> because i can fill video ram from userspace.Read and write to this DMA  
> param memory from userspace is not having any effect. Also video RAM  
> memory that i filled up is not getting written to the framebuffer device  
> when DMA is started. Also one more info that i noted was that values  
> assigned to logical addresses in kernel space are not reflected in  
> userspace after mmap. The values in userspace show different values  
> compared to that in kernel space.
> This is a bit confusing for me.

For me too.

> Why is this happening?? Have I missed  
> any information??

Yes, UIO is not for devices that are already supported by other subsystems.

> Am i on the right path??

I don't think so, unless you can provide good technical reasons for your
concept.

Thanks,
Hans

>
> regards,
> vijai
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