On Thu, 2014-10-23 at 17:33 +0300, Marcel Apfelbaum wrote: > On Thu, 2014-10-23 at 07:57 -0600, Alex Williamson wrote: > > On Thu, 2014-10-23 at 13:44 +0000, Stuart Yoder wrote: > > > > > > > -----Original Message----- > > > > From: Alex Williamson [mailto:alex.williamson@xxxxxxxxxx] > > > > Sent: Wednesday, October 22, 2014 1:33 PM > > > > To: Marcel Apfelbaum > > > > Cc: linux-pci@xxxxxxxxxxxxxxx; bhelgaas@xxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; marcel@xxxxxxxxxx; > > > > mst@xxxxxxxxxx; 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.williamson@xxxxxxxxxx> > > > > > 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 <marcel.a@xxxxxxxxxx> > > > > > --- > > > > > 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. > > > > Yes, when you set a driver_override on a device you cancel it by writing > > a NULL string to the same interface. The problem is that here we have a > > new entity in the driver scan that keeps re-applying the driver_override > > as devices are scanned with no way to stop it. So you can certainly > > undo the immediate effect and bind the device to another driver, but if > > the device is removed and re-scanned there's no way to stop if from > > re-applying the override. Thanks, > Hi Alex, > > I checked the above scenario and after driver_override is cleared > an we do bind/unbind, the mapping defined in the command line > does not apply anymore. > > My steps were: > 1. define the override in command-line -> the mapped driver is used instead of the native one > 2. unbind the device from the slot -> no driver for device > 3. remove the driver_override mapping form the slot -> no mapping defined > 3, bind the device again -> native driver in use. That's not the scenario I'm describing. Use the remove and rescan sysfs attributes to do a software hotplug and you'll see that the driver_override will always be re-applied to the device. For example: # echo "" > /sys/bus/pci/devices/0000:02:00.0/driver_override # echo 1 > /sys/bus/pci/devices/0000:02:00.0/remove # echo 1 > /sys/bus/pci/rescan # cat /sys/bus/pci/devices/0000:02:00.0/driver_override I expect the last step will show the original override re-applied. Thanks, Alex -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
