Re: [PATCH V2] video: implement a simple framebuffer driver

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Tomasz,

On Monday 29 April 2013 23:15:13 Tomasz Figa wrote:
> On Thursday 11 of April 2013 11:56:31 Laurent Pinchart wrote:
> > On Monday 08 April 2013 17:16:37 Andrew Morton wrote:
> > > On Wed,  3 Apr 2013 20:39:43 -0600 Stephen Warren wrote:
> > > > A simple frame-buffer describes a raw memory region that may be
> > > > rendered to, with the assumption that the display hardware has
> > > > already been set up to scan out from that buffer.
> > > > 
> > > > This is useful in cases where a bootloader exists and has set up the
> > > > display hardware, but a Linux driver doesn't yet exist for the
> > > > display hardware.
> > > > 
> > > > ...
> > > > 
> > > > +config FB_SIMPLE
> > > > +	bool "Simple framebuffer support"
> > > > +	depends on (FB = y) && OF
> > > 
> > > It's sad that this simple little thing requires Open Firmware.  Could
> > > it be generalised in some way so that the small amount of setup info
> > > could be provided by other means (eg, module_param) or does the
> > > dependency go deeper than that?
> > 
> > I second that request. I like the idea of a simple framebuffer driver if
> > it helps deprecating fbdev in the long term, but I don't want it to
> > offer an excuse not to implement a DRM/KMS driver. In particular adding
> > DT bindings would force us to keep supporting the ABI for a (too) long
> > time.
> 
> Well, there is also at least one legitimate use case for this driver.
> 
> I believe there exist embedded devices on which there is no need to
> dynamically control the framebuffer. It needs one time initialization,
> usually in bootloader, and then it is used as is, using constant
> parameters as long as the system is running.
> 
> I doubt there is a need for any KMS (or any other control) driver for such
> devices - dumb framebuffer driver would be everything needed in such case.

As we want to deprecate the fbdev API we would need to move to KMS at some 
point anyway, even if the device can't be controlled. I don't think writting 
such a KMS driver would be that difficult.

-- 
Regards,

Laurent Pinchart