Re: [PATCH v10 0/9] Add the I3C subsystem

vitor
2018-11-16T12:32:04Z

Hi Boris,

On 15/11/18 19:00, Boris Brezillon wrote:
> On Thu, 15 Nov 2018 18:03:47 +0000
> vitor <vitor.soares@synopsys.com> wrote:
>
>> Hi Boris,
>>
>>
>> On 15/11/18 15:28, Boris Brezillon wrote:
>>> On Thu, 15 Nov 2018 16:01:37 +0100
>>> Wolfram Sang <wsa@the-dreams.de> wrote:
>>>
>>>> Hi Boris,
>>>>
>>>>> What we could do though, is expose I3C devices that do not have a
>>>>> driver in kernel space, like spidev does.
>>>> ...
>>>>
>>>>> Mark, Wolfram, Arnd, Greg, any opinion?
>>>> Is there a benefit for having drivers in userspace? My gut feeling is to
>>>> encourage people to write kernel drivers. If this is, for some reason,
>>>> not possible for some driver, then we have a use case at hand to test
>>>> the then-to-be-developed userspace interface against. Until then, I
>>>> personally wouldn't waste effort on designing it without a user in
>>>> sight.
>>> I kind of agree with that. Vitor, do you have a use case in mind for
>>> such userspace drivers? I don't think it's worth designing an API for
>>> something we don't need (yet).
>> My use case is a tool for tests, lets say like the i2c tools.
> What would you like to test exactly?
>
>> There is
>> other subsystems, some of them mentioned on this thread, that have and
>> ioctl system call or other method to change parameters or send data.
> I don't think they added the /dev interface before having a real use
> case for it.
>
>>
>> I rise this topic because I really think it worth to define now how this
>> should be design (and for me how to do the things right) to avoid future
>> issues.
> Actually it should be done the other way around: you should have a real
> need and the /dev interface should be designed to fulfill this need.
> Based on this real use case we can discuss other potential usage that
> might appear in the future and try to design something more
> future-proof, but clearly, this userspace interface should be driven by
> a real/well-defined use case.
>
> Also, exposing things to userspace is way more risky than adding a new
> in-kernel subsystem/framework, because it then becomes part of the
> stable ABI.
>
> To make things clearer, I'm not against the idea of exposing I3C
> devices (or I3C buses) to userspace, but I'd like to understand what you
> plan to do with that. If this is about testing, what kind of tests
> you'd like to run. If this is about developing drivers in userspace,
> why can't these be done in kernel space (license issues?), and what
> would those drivers be allowed to do?

Basically I need a tool that help me during the development and to avoid
me to write a dummy driver for each device that I test.

For instances do some read/write, get/set ccc commands, if something
goes wrong during the bus initialization have a to debug etc...

For me this is a valid use case and I imagine when people start to
develop in i3c this interface will help everyone.

Best regards,

Vitor Soares