Re: spi: OF module autoloading is still broken

[Brian Norris <computersforpeace@gmail.com>]

Hi Javier,

On Mon, Nov 16, 2015 at 06:32:22PM -0300, Javier Martinez Canillas wrote:
> On 11/16/2015 05:47 PM, Brian Norris wrote:
> > On Mon, Nov 16, 2015 at 05:00:43PM -0300, Javier Martinez Canillas wrote:
> >> Now that I think about it, there is another issue and is that today spi:foo
> >> defines a namespace while changing to of: will make the namespace flat so
> >> a platform driver that has the same vendor and model will have the same
> >> modalias.
> >>
> >> IOW, for board files will be platform:bar and i2c:bar while for OF will be
> >> of:NfooT<NULL>Cfoo,bar in both cases. I wonder if we should reuse the type
> >> for that and store the subsystem prefix there. What do you think?
> > 
> > I'm not sure I understand all the issues here to be able to comment
> > properly. But I bet someone else might.
> > 
> > (For me, it might help if you had a more concrete example to speak of.)
> >
> 
> From a quick look I couldn't find a real example (that doesn't mean there
> isn't one) but I'll make one just to explain the problem.
> 
> Let's suppose you have 3 different IP's blocks (i.e: pmics) from the same
> vendor. The IP's are quite similar but only differ in that use a different
> bus to communicate with the SoC.

Ah, I thought that's what you might have meant, but then I reread enough
times that I confused myself. I think my first understanding was correct
:)

> So you could have a core driver and transport drivers for SPI and I2C.
> 
> So currently you could use the not too creative compatible strings compatible
> string "acme,my-pmic" in all the drivers and is not a problem because the SPI
> and I2C subsystem will always report the MODALIAS uevent as:
> 
> MODALIAS=i2c:my-pmic and MODALIAS=spi:my-pmic
> 
> so as far as there is a "my-pmic" entry in the SPI and I2C id tables, module
> autoload will work and the match will also work since that happens per bus_type.
> 
> But if SPI and I2C are migrated to OF modalias reporting, then both I2C and SPI
> will report (assuming the device node is called pmic in both cases):
> 
> MODALIAS=of:NpmicT<NULL>Cacme,my-pmic
> 
> That's what I meant when said that the modalias namespace is flat in the case of
> OF but is separated in the case of board files and the current implementation.

Thanks for the additional explanation.

> What currently the drivers are doing is to name the model my-pmic-{i2c,spi,etc}
> but I think that the subsystem information should be explicitly present in the
> OF modalias information as it is for legacy device registration.

Lest someone else wonder whether this is theoretical or not, I'll save
them the work in pointing at an example: "st,st33zp24". See:

Documentation/devicetree/bindings/security/tpm/st33zp24-*.txt

and the code is in drivers/char/tpm/st33zp24/, sharing the same core
library, suggesting that the devices really are the same except simply
the bus.

In my limited opinion, then, it seems like a good idea to still try to
separate the bus namespaces when reporting module-loading information.

Brian