Re: mechanism to allow a driver to bind to any device

[Kim Phillips <kim.phillips@linaro.org>]

On Mon, 31 Mar 2014 20:23:36 +0000
Stuart Yoder <stuart.yoder@freescale.com> wrote:

> > From: Greg KH [mailto:gregkh@linuxfoundation.org]
> > Sent: Monday, March 31, 2014 2:47 PM
> > 
> > On Mon, Mar 31, 2014 at 06:47:51PM +0000, Stuart Yoder wrote:
> > > I also, was at the point where I thought we should perhaps just
> > > go with current mechanisms and implement new_id for the platform
> > > bus...but Greg's recent response is 'platform devices suck' and it
> > sounds
> > > like he would reject a new_id patch for the platform bus.  So it kind
> > > of feels like we are stuck.
> > 
> > ids mean nothing in the platform device model, so having a new_id file
> > for them makes no sense.
> 
> They don't have IDs like PCI, but platform drivers have to match on
> something.  Platform device match tables are based on compatible strings.
> 
> Example from Freescale DMA driver:
>   static const struct of_device_id fsldma_of_ids[] = {
>         { .compatible = "fsl,elo3-dma", },
>         { .compatible = "fsl,eloplus-dma", },
>         { .compatible = "fsl,elo-dma", },
>         {}
>   };
> 
> The process of unbinding, setting a new_id, and binding to vfio would work
> just like PCI:
> 
>    echo ffe101300.dma > /sys/bus/platform/devices/ffe101300.dma/driver/unbind
>    echo fsl,eloplus-dma > /sys/bus/platform/drivers/vfio-platform/new_id

In platform device land, we don't want to pursue the
new_id/match-by-compatible methodology: we know exactly which specific
device (not device types) we want bound to which driver, so we just
want to be able to simply:

echo fff51000.ethernet | sudo tee -a /sys/bus/platform/devices/fff51000.ethernet/driver/unbind
echo fff51000.ethernet | sudo tee -a /sys/bus/platform/drivers/vfio-platform/bind

and not get involved with how PCI "doesn't simply do that," independent
of autoprobe/hotplug.

Kim