Re: [PATCH] arm: Add Kconfig entry to select CONFIG_DTB_FILE

[Michal Orzel <michal.orzel@xxxxxxx>]

On 08.03.2021 12:28, Jan Beulich wrote:
> On 08.03.2021 12:02, Michal Orzel wrote:
>> On 08.03.2021 11:00, Jan Beulich wrote:
>>> On 08.03.2021 10:52, Michal Orzel wrote:
>>>> +config DTB_FILE
>>>> +  string "Absolute path to device tree blob"
>>>> +  default ""
>>>> +  depends on LINK_DTB
>>>> +  ---help---
>>>> +    When using a bootloader that has no device tree support or when there
>>>> +    is no bootloader at all, use this option to specify the absolute path
>>>> +    to a device tree that will be linked directly inside Xen binary.
>>>
>>> How is selecting LINK_DTB but leaving DTB_FILE at an empty string
>>> different from not having a LINK_DTB setting at all?
>>>
>> LINK_DTB acts as a switch to allow setting the dtb path. Not having LINK_DTB 
>> option will result in
>> a build failure each time the user does not want to embed dtb into 
>> Xen(DTB_FILE is empty).
> 
> Which isn't any different from having LINK_DTB and leaving the
> string empty, is it? I.e. imo no improved user experience.
> 
>> I do not see why someone would want to select LINK_DTB leaving DTB_FILE as 
>> an empty string.
> 
> People may not "want" to, but simply think accepting the default
> is fine, considering they've already said to link in some DTB.
> It may be obvious to you that there's no good default here, but
> it may not be to the person configuring their Xen. I'm guessing
> here, but did you try leaving out the default line? Would this
> make kconfig insist on the person to type in something? (Likely
> an empty string would still be accepted. As would be a relative
> path, despite what the help text says; I guess some forms of
> relative paths may even work.)
> 
There is no option here to make kconfig insist on person to type something.
There is one solution. If I change in here:
https://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=xen/arch/arm/Makefile;h=16e6523e2cc6072b7d4cbcdeaf4726b7a9b1d381;hb=HEAD#l71
from:
ifdef CONFIG_DTB_FILE
to:
ifneq ($(CONFIG_DTB_FILE),"")
then if user selects LINK_DTB but does not provide dtb path, the dtb will not 
be embedded into Xen.
> Jan
> 

Michal