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

[Tudor Ambarus]

On 02.01.2023 13:48, Michael Walle wrote:
> Hi,

Hi,

> Am 2023-01-02 10:37, schrieb Tudor Ambarus:
> > Hi,
> >
> > On 18.11.2022 17:30, Mark Brown wrote:
> > > On Fri, Nov 18, 2022 at 03:14:58PM +0100, Michael Walle wrote:
> > > > From: Tudor Ambarus <tudor.ambarus@xxxxxxxxxxxxx>
> > >
> > > > > +  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.

> 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.