On Wed, Oct 06, 2021 at 11:12:37PM PDT, Greg Kroah-Hartman wrote:
On Wed, Oct 06, 2021 at 10:58:59PM -0700, Zev Weiss wrote:
On Wed, Oct 06, 2021 at 10:23:33PM PDT, Greg Kroah-Hartman wrote:
> On Wed, Oct 06, 2021 at 05:09:46PM -0700, Zev Weiss wrote:
> > This is simply the bin_attribute analog to sysfs_remove_file_self().
>
> No, no binary sysfs file should be triggering a remove.
>
> binary sysfs files are "pass-through-only" from userspace to hardware,
> the kernel should not be even knowing what is read/written to them.
>
> What do you think this is needed for?
>
So, I initially set out to be able to activate/deactivate specific DT nodes
at runtime by using the device-tree "reserved" status as defined in the spec
(but not currently used anywhere in the kernel) to mean essentially "create
a device for this but don't bind a driver to it" (leaving it to userspace to
invoke bind/unbind or similar), and added initial support for the specific
driver I'm concerned with at the moment (aspeed-smc) -- that was the
previous patch series linked in the cover letter of this one.
In the discussion of that series, Rob suggested as an alternate approach:
> Another possibility is making 'status' writeable from userspace. It is
> just a sysfs file.
That seemed sort of appealing to me, and this seemed like the most obvious
way to go about implementing it. Given that DT properties are binary
attributes, I gather you'd consider that a non-starter though?
Why would a text attribute of "status" be a binary sysfs file? That
feels really wrong as again, binary sysfs files are not supposed to be
parsed or handled by the kernel at all, they are only a pass-through.
Well, at present all device tree properties are binary sysfs files
regardless of type, and from a brief git history check it appears
they've been that way since DT sysfs support was introduced in commit
75b57ecf9d1d ("of: Make device nodes kobjects so they show up in
sysfs").
On the surface it seems like it would make sense for string properties
like status to be text files instead of binary, but (a) looking at some
of the discussion that preceded that patch, it sounds like there may be
some ambiguity regarding what the "true" types of different properties
actually are [0], and (b) changing the contents of those files from e.g.
"okay\0" to "okay\n" seems likely to lead to broken userspace, so I'd
guess it's probably moot anyway.
[0] https://lore.kernel.org/lkml/1363801579.17680.3.camel@pasglop/
Zev
