From mboxrd@z Thu Jan 1 00:00:00 1970 From: Scott Wood Subject: Re: RFC: (re-)binding the VFIO platform driver to a platform device Date: Wed, 9 Oct 2013 14:49:51 -0500 Message-ID: <1381348191.7979.348.camel@snotra.buserror.net> References: <20131002203735.GA10871@kroah.com> <1380748121.12932.89.camel@snotra.buserror.net> <20131002211631.GA11914@kroah.com> <1380749715.12932.109.camel@snotra.buserror.net> <20131002234009.GA27714@kroah.com> <1380825207.12932.151.camel@snotra.buserror.net> <20131003185434.GA26123@kroah.com> <1380827494.12932.161.camel@snotra.buserror.net> <20131003203226.GB27336@kroah.com> <9F6FE96B71CF29479FF1CDC8046E15036DDA62@039-SN1MPN1-002.039d.mgd.msft.net> <20131009191652.GA18611@kroah.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: Yoder Stuart-B08248 , Wood Scott-B07421 , Kim Phillips , Christoffer Dall , Alex Williamson , "linux-kernel@vger.kernel.org" , "a.motakis@virtualopensystems.com" , "agraf@suse.de" , Sethi Varun-B16395 , Bhushan Bharat-R65777 , "peter.maydell@linaro.org" , "santosh.shukla@linaro.org" , "kvm@vger.kernel.org" To: "gregkh@linuxfoundation.org" Return-path: In-Reply-To: <20131009191652.GA18611@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Wed, 2013-10-09 at 12:16 -0700, gregkh@linuxfoundation.org wrote: > On Wed, Oct 09, 2013 at 07:02:25PM +0000, Yoder Stuart-B08248 wrote: > > Have been thinking about this issue some more. As Scott mentioned, > > 'wildcard' matching for a driver can be fairly done in the platform > > bus driver. We could add a new flag to the platform driver struct: > > > > diff --git a/drivers/base/platform.c b/drivers/base/platform.c > > index 4f8bef3..4d6cf14 100644 > > --- a/drivers/base/platform.c > > +++ b/drivers/base/platform.c > > @@ -727,6 +727,10 @@ static int platform_match(struct device *dev, struct device_driver *drv) > > struct platform_device *pdev = to_platform_device(dev); > > struct platform_driver *pdrv = to_platform_driver(drv); > > > > + /* the driver matches any device */ > > + if (pdrv->match_any) > > + return 1; > > + > > /* Attempt an OF style match first */ > > if (of_driver_match_device(dev, drv)) > > return 1; > > > > However, the more problematic issue is that a bus driver has no way to > > differentiate from an explicit bind request via sysfs and a bind that > > happened through bus probing. > > That was by design, nice to see I implemented it properly :) > > > I think something like the new flag in the snippet below would enable the platform > > bus to support platform drivers that only bind on explicit request: > > > > diff --git a/drivers/base/bus.c b/drivers/base/bus.c > > index 4c289ab..daf6d24 100644 > > --- a/drivers/base/bus.c > > +++ b/drivers/base/bus.c > > @@ -201,7 +201,7 @@ static ssize_t bind_store(struct device_driver *drv, const char *buf, > > int err = -ENODEV; > > > > dev = bus_find_device_by_name(bus, NULL, buf); > > - if (dev && dev->driver == NULL && driver_match_device(drv, dev)) { > > + if (dev && dev->driver == NULL && driver_match_device(drv, dev, 1)) { > > Magic flags are the spawn of your favorite anti-$DIETY. I'm never going > to accept that, sorry. > > If you really want to do something "special" for the platform bus, then > do it only for the platform bus. But even then, you'll find me arguing > that you really don't want to do it at all, sorry. It's not (or shouldn't be) special for the platform bus. The "don't bind by default" flag (note that I am *not* referring to the above code snippet) would be useful for VFIO PCI as well, as it would replace the hacky and racy usage of new_id. > I'm still yet to be convinced this is even an issue at all, but maybe > that's just the jetlag talking... If this is because you think we should use new_id, we just had a discussion in this thread about why that's no good. -Scott