Re: spidev: That spidev in the DT issue again...

[Trent Piepho <tpiepho@xxxxxxxxxx>]

On Sat, 2018-02-03 at 08:31 +0000, Henry Gomersall wrote:
> On 02/02/18 18:58, Trent Piepho wrote:
> > > The clear use case for more flexibility in the system is around FPGA
> > > based SoCs (in my case a Zynq). In such a scenario the use of userspace
> > > is a natural complement to runtime configurable hardware blocks. It
> > > would really ease access to (at least somewhat) correct use of the
> > > driver if it could be recognised that the kernel might not actually need
> > > to know what's on the end of an SPI bus.
> > 
> > I've got a patch that adds "driver_override" to the SPI bus.  This
> > already exists on the PCI bus, platform bus, and AMBA bus.
> > 
> 
> Thanks for that. What's the status of the patch currently? I can't see
> it on patchwork...
> 
> Looking back at your earlier email you point out doing this through udev
> rules, which is IMO a good way to solve the problem

I'll need to send it again.

> > 
> > It does not solve the problem of creating and destroying SPI slaves
> > dynamically at run time.  This can be solved (and it way that isn't
> > specific to spidev), via:
> > * Copying the I2C new_device system, which allows this with limitations
> > and in a SPI (and I2C) specific way.
> > * Incorporation of the dynamic DT fragment loading system, which solves
> > this with far less limitation and it manner that is not bus specific.
> 
> Is this an aspiration, a WIP, or just a thought?

The new_device was presented as a patch recently, but was linked to
spidev.  I don't remember seeing a v2 that was not linked to spidev,
which seemed straightforward, but I easily could have missed it.

Most of the dynamic DT pieces are already in the kernel, for example
ce79d54ae44 "spi/of: Add OF notifier handler".  I think the configfs
part is still unmerged, see https://patchwork.kernel.org/patch/5179621/
I don't know why it's not in already.  This would solve the problem of
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