> -----Original Message----- > From: Marcel Apfelbaum [mailto:marce...@redhat.com] > Sent: Thursday, October 23, 2014 7:32 AM > To: Alex Williamson > Cc: linux-...@vger.kernel.org; bhelg...@google.com; > linux-kernel@vger.kernel.org; mar...@redhat.com; > m...@redhat.com; Yoder Stuart-B08248 > Subject: Re: [PATCH v4] PCI: add kernel parameter to override devid<->driver > mapping. > > On Wed, 2014-10-22 at 12:32 -0600, Alex Williamson wrote: > > [cc+ stuart] > > > > On Mon, 2014-10-20 at 17:04 +0300, Marcel Apfelbaum wrote: > > > Scanning a lot of devices during boot requires a lot of time. > > > On other scenarios there is a need to bind a driver to a specific slot. > > > > > > Binding devices to pci-stub driver does not work, > > > as it will not differentiate between devices of the > > > same type. Using some start scripts is error prone. > > > > > > The solution leverages driver_override functionality introduced by > > > > > > commit: 782a985d7af26db39e86070d28f987cad21313c0 > > > Author: Alex Williamson <alex.william...@redhat.com> > > > Date: Tue May 20 08:53:21 2014 -0600 > > > > > > PCI: Introduce new device binding path using > > > pci_dev.driver_override > > > > > > In order to bind PCI slots to specific drivers use: > > > pci=driver[xxxx:xx:xx.x]=foo,driver[xxxx:xx:xx.x]=bar,... > > > > > > Signed-off-by: Marcel Apfelbaum <marce...@redhat.com> > > > --- > > > v3 -> v4: > > > - Addressed Alex Williamson's comments: > > > - Modified the type of driver_override_entry's fields > > > - Used PCI_DEVFN when appropriated > > > - Removed redundant checks > > > - Replaced BUG_ON with pr_err messages > > > - Simpler command line parsing > > > - Addressed Michael S. Tsirkin comments > > > - removed DRIVER_OVERRIDE_NAME_LENGTH limitation > > > v2 -> v3: > > > - Corrected subject line > > > v1 -> v2: > > > - Addressed Michael S. Tsirkin comments > > > - Removed 32 slots limitation > > > - Better handling of memory allocation failures > > > (preferred BUG_ON over error messages) > > > - Addressed Alex Williamson's comments: > > > - Modified commit message to show parameter usage more clear. > > > - I preferred to re-use parse_args instead of manually using > > > strstr in order to better comply with command line parsing > > > rules. > > > - I didn't use any locking when parsing the command line args > > > (see parse_done usage) assuming that first call will be > > > early in system boot and no race can occur. Please correct > > > me if I am wrong. > > > > > > Notes: > > > - I have further ideas on top of this patch based on your reviews. > > > I thought of: > > > - Use wildcards to specify entire buses/devices, something like: > > > driver[0001:02:*.*]=pci-stub > > > - Use comma to separate several devices: > > > driver[0001:02:03.4,0001:02:04.0,...]=pci-stub > > > - Make domain optional: > > > driver[00:03.0]=pci-stub > > > > > > Comments will be appreciated, > > > Thanks, > > > Marcel > > > Documentation/kernel-parameters.txt | 4 ++ > > > drivers/pci/bus.c | 111 > > > ++++++++++++++++++++++++++++++++++++ > > > drivers/pci/pci.c | 2 + > > > 3 files changed, 117 insertions(+) > > > > The driver_override feature that we're making use of here is also going > > to be supported by platform devices and potentially more bustypes in the > > future, so I'm concerned that making a pci specific kernel parameter is > > too shortsighted. Instead we could hook on to BUS_NOTIFY_ADD_DEVICE for > > bustypes that support driver_override so we can have a common interface. > The real question here if those bus types/devices would benefit from this > feature, and I also must confess that I have no knowledge of the other buses. > Can anyone confirm that it does make sense for them?
We don't have vfio-platform in use yet, so not much actual real world user experience yet. But, I think it makes sense. Especially, given that we are inventing a kernel parameter I think we should design the syntax so that it can work buses can implement support for this. The driver_override mechanism is not bus specific, so let's not make the kernel parameter bus specific. > > Perhaps: > > > > driver_override=pci,0000:02:00.0=pci-stub;platform,fakename=vfio-platform > > > > Finding delimiters that don't conflict may be challenging. Also, can we > > assume that bus-name:dev-name is unique for every bustype? It is for > > pci, platform? > For PCI, sure the domain:bus:dev.func is unique, for platform I have no idea, > can anyone that knows "platform" confirm or deny? Yes, dev-name will be unique. All platform devices are under a single platform bus. Stuart
