From mboxrd@z Thu Jan 1 00:00:00 1970 From: Egbert Eich Subject: Re: [Linux-fbdev-devel] Re: Who is stomping PCI config space? Date: Sat, 5 Mar 2005 20:07:13 +0100 Message-ID: <16938.865.144516.757019@xf14.local> 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> <1109976305.5611.312.camel@gaston> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit In-Reply-To: benh@kernel.crashing.org wrote on Saturday, 5 March 2005 at 09:45:04 +1100 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: Benjamin Herrenschmidt Cc: Egbert Eich , Xserver development , Linux Fbdev development list , Jesse Barnes Benjamin Herrenschmidt writes: > 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. If we can control this. However if we can there is not much difference which apporach we take. > > > 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... That's the apporach we took when we implemented this in X. It was the safest bet. Egbert.