From mboxrd@z Thu Jan 1 00:00:00 1970 From: Benjamin Herrenschmidt Subject: Re: [Linux-fbdev-devel] Re: Who is stomping PCI config space? Date: Sat, 05 Mar 2005 09:45:04 +1100 Message-ID: <1109976305.5611.312.camel@gaston> References: <9e4733910503031103552514b9@mail.gmail.com> <1109891245.5611.246.camel@gaston> <9e473391050303161559c17955@mail.gmail.com> <9e47339105030319037f083f7@mail.gmail.com> <1109918459.5610.273.camel@gaston> <16936.20345.249542.65736@xf14.local> <9e473391050304095812a11208@mail.gmail.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit In-Reply-To: <9e473391050304095812a11208@mail.gmail.com> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: xorg-bounces@lists.freedesktop.org Errors-To: xorg-bounces@lists.freedesktop.org Content-Type: text/plain; charset="us-ascii" To: Jon Smirl Cc: Egbert Eich , Linux Fbdev development list , Xserver development , Jesse Barnes On Fri, 2005-03-04 at 12:58 -0500, Jon Smirl wrote: > In the past Jesse Barnes has suggested a completely different approach > to VGA sharing. Instead of each VT trying to control which VGA device > is enabled we keep them all turned off. Then on each access we turn > VGA support on just long enough for the access and then turn it back > off. That's what I had in mind too. > To make this work we have to have a kernel based 'token' for who has > the VGA at the moment. This scheme lets multiuser systems work. For > big IA64 machines which can support multiple simultaneous VGAs we just > have multiple tokens. That means that the arbitrer must need to know how to enable/disable VGA decoding on a per-card basis (when it's possible at all), or active collaboration with the kernel driver. Also, you can't prevent the interrupts from happening unless you also disable them on your card. > We would just ban VGA access from interrupt context, if you really > needed VGA access you would use a workqueue which can be scheduled > from the interrupt. None of my driver work needs VGA access from > interrupt context, is this true for all drivers? I need access to the > video hardware, but not access to the VGA support. It's not enough. There is a variety of cases where the only way to turn off VGA access is to turn off IO & MEM decoding completely on the card... Ben.