Re: [PATCH 1/8] spi: dt-bindings: Introduce spi-cs-setup-ns property

[Michael Walle]

> > > > > > +  spi-cs-setup-ns:
> > > > > > +    description:
> > > > > > +      Delay in nanosecods to be introduced by the controller 
> > > > > > after CS is
> > > > > > +      asserted.
> > > >
> > > > > Does this need a type as the spi-cs-setup-ns is apparently just 
> > > > > 16bit? At
> > > > > least the driver uses it that way.
> > > >
> > > > > But IMHO this should just be a normal uint32 value to be consistent 
> > > > > with
> > > > > all the other properties. Also the max value with 16bit will be 
> > > > > 'just'
> > > > > 65us.
> > > >
> > > > Making it 32 bit does seem safer.  I've applied the series
> > >
> > > Thanks. There are few implications to consider before making this 
> > > prop a
> > > u32, and I'd like to check them with you.
> > >
> > > struct spi_delay will have to be updated to have a u32 value, now 
> > > it's a
> > > u16. This means that we'll have to update spi_delay_to_ns() to either
> > > return a s64 or to add a u64 *delay parameter to the function so that 
> > > we
> > > can still handle the conversions from usecs and the error codes in 
> > > the
> > > SPI_DELAY_UNIT_SCK case. Then all its callers have to be updated to
> > > consider the u64 delay.
> >
> > I was talking about the device tree property. Even if the driver 
> > continue
> > to use just 16bit, the DT property could be 32bit IMHO.
>
> but then you'll have an implicit cast to u16 at:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/spi/spi.c#n2314
> which will make the u32 dt prop misleading.

Nothing will prevent you from checking for a valid range and return an
error :)
But I agree, that converting the u16 to u32 in the driver is probably
the better way.

> > At the moment, the schema says its 32bit (if I'm not mistaken, because
> > it doesn't have a type), but the driver will parse the property as
> > 16bit and your device tree also has this /bits/ thingy. So regardless
> > if the driver is using 16bit or 32bit for the value, there seems to be
> > a discrepancy between the schema and the devicetree (and driver).
>
> okay, thanks for pointing it out. Let's decide how we fix this.
>
> > All other properties are just the regular 32bit values, thus I was
> > suggesting to change the DT property to 32bit.
>
> If we want to change the dt prop to 32bit I think we should also handle
> the parsed value as u32, not as u16.

Strictly speaking, your device tree is wrong, because the schema
already says it's 32bit.

-michael