Re: Exposing ROM's though sysfs

[Jesse Barnes <jbarnes@engr.sgi.com>]

On Tuesday, August 3, 2004 6:57 pm, Benjamin Herrenschmidt wrote:
> Jesse did a pretty good summary of what features need to be provided
> though. Note also that this "arbitration" layer may also need an in-kernel
> API for things like vgacon or whatever may want to "grab" access to the
> VGA device.

Good point, I forgot about that.  Theoretically, as long as a device has been 
POSTed, vgacon should work just fine with some small tweaks on platforms that 
allow mapping of the VGA framebuffer.

> I suggest that at this point, we don't try to bother with simultaneous
> access to devices on separate PCI domains, but just use an in-kernel
> semaphore to arbitrate the single user at a given point in time who "owns"
> the VGA access, whatever bus it is on. So we need 2 things, both in-kernel
> and for userland:

Sounds good.  Cards usually POST pretty quickly, so that won't be a problem 
until someone puts 32 cards in a system (oh wait, that's not too far off :).

>  - A way to identify a VGA device on a given bus. Could this be a PCI
> ID (or in kernel a pci_dev ?). That would mean no support for non-PCI
> stuffs, how bad would that be ?

I personally don't care about anything but PCI, AGP and PCI-Express, but you 
make a good point about embedded stuff.

>  - Userland should use read/write for IOs imho, either to a /dev device
> (with maybe an ioctl to switch between PIO and VGA mem, though mmap is
> better for the later) or to some sysfs entry (in which case, can we add
> mmap call to a sysfs attribute ? last time I looked, it wasn't simple).

Yeah, that sounds reasonable.  I'd vote for a real device as opposed to sysfs 
files, for now at least.

Jesse