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

[Stefan Herbrechtsmeier]

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.

> Then we can use the u32() function and do a mask.

The driver cast away the unseeded bits.

>>
>> [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
   Stefan