Subject: [PATCH v3] platform: Make platform_bus device a platform device

From: [email-masked] (Greg Kroah-Hartman)
Date: Wed, 23 Jul 2014 12:34:34 -0700

On Wed, Jul 23, 2014 at 06:16:02PM +0100, Pawel Moll wrote:
> On Tue, 2014-07-22 at 19:15 +0100, Greg Kroah-Hartman wrote:
> > > > diff --git a/arch/arm/mach-imx/devices/devices.c b/arch/arm/mach-imx/devices/devices.c
> > > > index 1b4366a..48c3817 100644
> > > > --- a/arch/arm/mach-imx/devices/devices.c
> > > > +++ b/arch/arm/mach-imx/devices/devices.c
> > > > @@ -24,12 +24,12 @@
> > > > 
> > > >  struct device mxc_aips_bus = {
> > > >         .init_name      = "mxc_aips",
> > > > -       .parent         = &platform_bus,
> > > > +       .parent         = &platform_bus.dev,
> > > >  };
> > > > 
> > > >  struct device mxc_ahb_bus = {
> > > >         .init_name      = "mxc_ahb",
> > > > -       .parent         = &platform_bus,
> > > > +       .parent         = &platform_bus.dev,
> > > >  };
> > > > 
> > > >  int __init mxc_device_init(void)
> > > 
> > > Seems that the author meant to have those two bus devices hanging from
> > > the platform_bus in device hierarchy. Seems fair enough to me.
> > 
> > No, not at all, this is a different bus, put the root bus at the root of
> > the sysfs tree, not at some "arbritrary" point on a platform device.
> 
> I think the author considers platform bus is understood as a
> representation of the MMIO space (and he's not alone). So then he wants
> to represent the physical hierarchy of the interconnect to get it in
> separate places in the /sys/devices/* tree.

That's fine, but again, it's not a "child" of the platform bus.
Otherwise you could argue that all busses should belong under the
platform bus as well, which isn't going to happen.

> Whether it's a good thing to do or not, have no strong opinion, but can
> understand his approach. I don't think it's a big deal either way.

Great, make it NULL :)

> > > > diff --git a/drivers/char/tile-srom.c b/drivers/char/tile-srom.c
> > > > index bd37747..4e4b7a2 100644
> > > > --- a/drivers/char/tile-srom.c
> > > > +++ b/drivers/char/tile-srom.c
> > > > @@ -350,7 +350,7 @@ static int srom_setup_minor(struct srom_dev *srom, int index)
> > > >                        SROM_PAGE_SIZE_OFF, sizeof(srom->page_size)) < 0)
> > > >                 return -EIO;
> > > > 
> > > > -       dev = device_create(srom_class, &platform_bus,
> > > > +       dev = device_create(srom_class, &platform_bus.dev,
> > > >                             MKDEV(srom_major, index), srom, "%d", index);
> > > >         return PTR_ERR_OR_ZERO(dev);
> > > >  }
> > > 
> > > Again, non-platform device placed in the hierarchy.
> > 
> > Again, not ok.  If it's a platform device, it's a platform device, and
> > make it one.  If it isn't, like this one, make it a virtual device and
> > pass NULL here.
> 
> Yeah, I can't disagree here.
> 
> > > > diff --git a/drivers/mmc/host/sdhci-pltfm.c b/drivers/mmc/host/sdhci-pltfm.c
> > > > index 7e834fb..9a2b0d0 100644
> > > > --- a/drivers/mmc/host/sdhci-pltfm.c
> > > > +++ b/drivers/mmc/host/sdhci-pltfm.c
> > > > @@ -137,7 +137,7 @@ struct sdhci_host *sdhci_pltfm_init(struct platform_device *pdev,
> > > >                 dev_err(&pdev->dev, "Invalid iomem size!\n");
> > > > 
> > > >         /* Some PCI-based MFD need the parent here */
> > > > -       if (pdev->dev.parent != &platform_bus && !np)
> > > > +       if (pdev->dev.parent != &platform_bus.dev && !np)
> > > >                 host = sdhci_alloc_host(pdev->dev.parent,
> > > >                         sizeof(struct sdhci_pltfm_host) + priv_size);
> > > >         else
> > > 
> > > Special treatment for non-platform devices.
> > 
> > Ugh, why should you care?  I don't understand the logic here.
> 
> Neither do I, but maybe there is' some :-) I definitely wouldn't like to
> change the behaviour without checking with the maintainers.

Then let's ask :)

> > > > diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
> > > > index 3cbb57a..c14c36f 100644
> > > > --- a/drivers/scsi/hosts.c
> > > > +++ b/drivers/scsi/hosts.c
> > > > @@ -218,7 +218,7 @@ int scsi_add_host_with_dma(struct Scsi_Host *shost, struct device *dev,
> > > >                 goto fail;
> > > > 
> > > >         if (!shost->shost_gendev.parent)
> > > > -               shost->shost_gendev.parent = dev ? dev : &platform_bus;
> > > > +               shost->shost_gendev.parent = dev ? dev : &platform_bus.dev;
> > > >         if (!dma_dev)
> > > >                 dma_dev = shost->shost_gendev.parent;
> > > > 
> > > 
> > > shost_gendev is a generic (as in struct device, non-platform one)
> > > device, that is being explicitly placed in the hierarchy.
> > 
> > Then make it a virtual device, as that's what it is, replace this with
> > NULL.
> 
> Makes sense to me, I just wonder what the author meant.

With scsi code, who knows :)

> > > So it makes it 4, not 3 ;-) places where referencing platform_bus
> > > *maybe* makes some sense.
> > 
> > Nope, see above :)
> 
> Let me just point out that I'm just playing the devil's advocate
> here :-)

Of course, I'm not "shooting the messenger" at all, just pointing out
problems with the code, you didn't write it.

thanks,

greg k-h