> -----Original Message-----
> From: Alex Williamson [mailto:alex.william...@redhat.com]
> Sent: Wednesday, October 22, 2014 1:33 PM
> To: Marcel Apfelbaum
> 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.
>
> [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.
> Perhaps:
>
> driver_override=pci,0000:02:00.0=pci-stub;platform,fakename=vfio-platform
>
> Finding delimiters that don't conflict may be challenging.
I think what you proposed works-- <bus-name>,<bus-dev>=<driver>;
Think that will work for PCI, platform, and the new fsl-mc bus we are working
on.
> Also, can we
> assume that bus-name:dev-name is unique for every bustype? It is for
> pci, platform?
I think that has to be the case.
> It also seems like there's a question of how long should this override
> last and how does the user disable it?
Isn't that a general question for the "driver_overrride" mechanism?
I'm forgetting if the mechanism in the kernel now has a way to disable
it-- e.g. echo /dev/null > /sys/pci/devices/.../driver_override ??
So, it would last until explicitly disabled through sysfs.
> I think with pci-stub.ids=
> $VENDOR:$DEVICE a user can echo the IDs to the pci-stub/remove_id sysfs
> entry to cancel the effect. The only option here seems to be a reboot.
> Do we need a /sys/bus/pci/driver_overrides/{add_name,remove_name} for
> this interface? Thanks,
Thanks,
Stuart
