setting driver properties for a particular device

[Ian Lepore]

On Wed, 2019-05-29 at 13:31 +0300, Andriy Gapon wrote:
> On 29/05/2019 13:29, Michael Zhilin wrote:
> > Hi,
> > 
> > There are kenv and sysctl. Is it far from what you are looking for?
> 
> No.  When I said programmatically, I meant programmatically from
> within the kernel.
> 

Hmmm.  Whatever you do, it's going to amount to a conspiracy of
agreement between the driver that wants to set this info and the driver
that is expected to act on it.  So if you don't use the existing hints
mechanism, then you'll have to invent something new, and the gpioled
driver will have to be updated to also check that new mechanism to see
if there is any config info there that affects it.  I'm not sure that's
a big win over the slight inelegance of crafting a hint string at
runtime.

-- Ian


> > On Wed, May 29, 2019 at 1:19 PM Andriy Gapon <avg at freebsd.org
> > <mailto:avg at freebsd.org>> wrote:
> > 
> >     On 23/05/2019 14:15, Andriy Gapon wrote:
> >     > Author: avg
> >     > Date: Thu May 23 11:15:22 2019
> >     > New Revision: 348153
> >     > URL: https://svnweb.freebsd.org/changeset/base/348153
> >     >
> >     > Log:
> >     >   gpioled: add a new hint for initial state
> >     >   
> >     >   hint.gpioled.%d.state determines the initial state of the
> > LED when the
> >     >   driver takes control over it:
> >     >     0 - the LED is off
> >     >     1 - the LED is on
> >     >    -1 - the LED is kept as it was
> > 
> >     By the way, can anyone suggest a mechanism to set device
> > properties like this
> >     one _programmatically_ ?
> > 
> >     I am thinking of a case where I know exactly how everything is
> > wired on a
> >     platform.  And there is no FDT or alike support for it.  And
> > hints are not
> >     possible to set up correctly (e.g., bus numbers may float). 
> > So, I want to
> >     create a gpioled child on a specific bus and I want to set some
> > properties for
> >     the device.
> >     Of course, I can probably do something like
> > kern_setenv("hints.foo.X.bar", ...)
> >     using the child's name and unit number.  But that feels a bit
> > cumbersome.
> > 
> >     And this question is not about gpioled specifically.
> > 
> >     IVARs is definitely not the right mechanism, because it is
> > about bus-specific
> >     properties of devices on the bus.  So, it is not aware of
> > properties specific to
> >     a driver that attaches to a child device.
> > 
> > 
> >     -- 
> >     Andriy Gapon
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> 
>