On Wed, 2 Oct 2013 11:43:30 -0700 Christoffer Dall <christoffer.dall@xxxxxxxxxx> wrote: > On Wed, Oct 02, 2013 at 01:32:38PM -0500, Scott Wood wrote: > > On Wed, 2013-10-02 at 13:25 -0500, Yoder Stuart-B08248 wrote: > > > > > > > -----Original Message----- > > > > From: Christoffer Dall [mailto:christoffer.dall@xxxxxxxxxx] > > > > Sent: Wednesday, October 02, 2013 10:14 AM > > > > To: Alex Williamson > > > > Cc: Kim Phillips; gregkh@xxxxxxxxxxxxxxxxxxx; linux- > > > > kernel@xxxxxxxxxxxxxxx; a.motakis@xxxxxxxxxxxxxxxxxxxxxx; agraf@xxxxxxx; > > > > Yoder Stuart-B08248; Wood Scott-B07421; Sethi Varun-B16395; Bhushan > > > > Bharat-R65777; peter.maydell@xxxxxxxxxx; santosh.shukla@xxxxxxxxxx; > > > > kvm@xxxxxxxxxxxxxxx > > > > Subject: Re: RFC: (re-)binding the VFIO platform driver to a platform > > > > device > > > > > > > > Wouldn't a sysfs file to add compatibility strings to the vfio-platform > > > > driver make driver_match_device return true and make everyone happy? > > > > > > I had a similar thought. Why can't we do something like: > > > > > > echo "fsl,i2c" > /sys/bus/platform/drivers/vfio-platform/new_compatible > > > echo 12ce0000.i2c > /sys/bus/platform/drivers/vfio-platform/bind > > > > > > The first steps tell vfio-platform to register itself to handle > > > "fsl,i2c" compatible devices. The second step does the bind. > > > > Needing to specify the compatible is hacky (we already know what device > > we want to bind; why do we need to scrounge up more information than > > that, and add a new sysfs interface for extending compatible matches, > > and a more flexible data structure to back that up?), and is racy on > > buses that can hotplug (which driver gets the new device?). > > Why hacky? It seems quite reasonable to me that the user has to tell a > subsystem that from a certain point it should be capable of handling > some device. I think what Scott is saying is that the first echo above is somewhat redundant with the second: they're both talking to the vfio-platform driver about an i2c device. > As for the data structure, isn't this a simple linked list? > > The problem with the race seems to be a common problem that hasn't even > been solved for PCI yet, so I'm wondering if this is not an orthogonal > issue with a separate solution, such as a priority or something like > that. I agree; adding 'direct'/'atomic' functionality to the existing bind sysfs file, i.e., bind_store() logic to perform device_release_driver() logic if dev->driver != NULL, all under the same device_lock() is an independent problem from binding the VFIO platform driver to a platform device. > Yes, once you've added the new_compatible to the vfio-platform driver, > it's up for grabs from both the new and the old driver, but that could > be solved by always making sure that the vfio-platform driver is checked > first. not sure I understand the priority problem here - haven't looked at PCI yet - but, given the above 'atomic bind' functionality described above, the new and old driver wouldn't be requesting to bind to the same device simultaneously, no? > (I'm not familiar with these data structures, but I would imagine > something like re-inserting the vfio-platform driver in the > list/tree/... whenever adding a new_compatible value might possibly be > one solution). > > > What's wrong with a non-vfio-specific flag that a driver can set, that > > indicates that the driver is willing to try to bind to any device on the > > bus if explicitly requested via the existing sysfs bind mechanism? > > > It sounds more hackish to me to invent some 'generic' flag to solve a > very specific case. What you're suggesting would let users specify that > a serial driver should handle a NIC hardware, no? That sounds much much > worse to me. I thought that was the nature of VFIO drivers...it's a 'meta-' driver, used for enabling userspace drivers at large. Kim -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
