[PATCH 1/2] dm: core: Add functions to read 8/16-bit integers

[Simon Glass]

Hi Stefan,

On Thu, 14 Jul 2022 at 04:37, Stefan Herbrechtsmeier
<stefan.herbrechtsmeier-oss at weidmueller.com> wrote:
>
> Hi Simon,
>
> Am 14.07.2022 um 12:22 schrieb Simon Glass:
> > Hi Stefan,
> >
> > On Wed, 13 Jul 2022 at 10:08, Stefan Herbrechtsmeier
> > <stefan.herbrechtsmeier-oss at weidmueller.com> wrote:
> >>
> >> Hi Simon,
> >>
> >> Am 13.07.2022 um 17:28 schrieb Simon Glass:
> >>> Hi Stefan,
> >>>
> >>> On Tue, 12 Jul 2022 at 12:31, Stefan Herbrechtsmeier
> >>> <stefan.herbrechtsmeier-oss at weidmueller.com> wrote:
> >>>>
> >>>> Hi Simon,
> >>>>
> >>>> Am 12.07.2022 um 12:58 schrieb Simon Glass:
> >>>>> Hi Stefan,
> >>>>>
> >>>>> On Tue, 14 Jun 2022 at 07:22, Stefan Herbrechtsmeier
> >>>>> <stefan.herbrechtsmeier-oss at weidmueller.com> wrote:
> >>>>>>
> >>>>>> From: Stefan Herbrechtsmeier <stefan.herbrechtsmeier at weidmueller.com>
> >>>>>>
> >>>>>> Add functions to read 8/16-bit integers like the existing functions for
> >>>>>> 32/64-bit to simplify read of 8/16-bit integers from device tree
> >>>>>> properties.
> >>>>>>
> >>>>>> Signed-off-by: Stefan Herbrechtsmeier <stefan.herbrechtsmeier at weidmueller.com>
> >>>>>> ---
> >>>>>>
> >>>>>>     arch/sandbox/dts/test.dts |  2 ++
> >>>>>>     drivers/core/of_access.c  | 38 +++++++++++++++++++++++
> >>>>>>     drivers/core/ofnode.c     | 62 +++++++++++++++++++++++++++++++++++++
> >>>>>>     drivers/core/read.c       | 21 +++++++++++++
> >>>>>>     include/dm/of_access.h    | 32 +++++++++++++++++++
> >>>>>>     include/dm/ofnode.h       | 40 ++++++++++++++++++++++++
> >>>>>>     include/dm/read.h         | 65 +++++++++++++++++++++++++++++++++++++++
> >>>>>>     test/dm/test-fdt.c        | 19 ++++++++++++
> >>>>>>     8 files changed, 279 insertions(+)
> >>>>>
> >>>>> This looks good but is very expensive in terms of code size. Can you
> >>>>> update your u8 and u16 functions to reuse the existing u32 function
> >>>>> and just convert the value?
> >>>>
> >>>> The u32 function requires a 32 bit value inside the device tree because
> >>>> it checks the size and maybe swap the bytes.
> >>>>
> >>>> The u8 and u16 function requires only a 8 and 16 bit value inside the
> >>>> device tree.
> >>>
> >>> Yes that's true. What is the use case for these functions?
> >>
> >> The usb251xb driver requires this functions [1]. The usb251xb device
> >> tree binding [2] defines the ids as 16 bit values and the Linux driver
> >> use 8 bit for an unspecified property. Without this changes the driver
> >> doesn't satisfy the specification and is incompatible to the Linux driver.
> >
> > I wonder if that binding is a bit ambiguous. From what I have seen we
> > normally use a single cell for int values, partly so that fdtdump
> > works and partly because the format doesn't allow using any less space
> > anyway.
> >
> > IMO that binding should use a whole cell for the byte and u16 values.
>
> How should we go on? The specification is 5 years old. I can ignore the
> specification  and remove the "/bits/ 16" from my device tree source.

I believe either would work, since reading a u32 from the device tree
and masking it would achieve the same result. The problem with the
current u32 function is that it requires 4 bytes.

IMO the binding is odd, but I don't think you can just change it.

>
> > Then we can use the u32() function and do a mask.
>
> The driver cast away the unseeded bits.

OK.

Anyway as Heinrich says below, most boards won't use these functions.
I hope that other drivers don't start using u8 and u16 values when a
u32 will do.

Reviewed-by: Simon Glass <sjg at chromium.org>

>
> >>
> >> [1] https://lists.denx.de/pipermail/u-boot/2022-June/486424.html
> >> [2]
> >> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/usb/usb251xb.txt
>      Stefan
>

Regards,
Simon