On 03/19/2013 02:54 AM, Mike Turquette wrote:
Quoting Arnd Bergmann (2013-03-16 07:56:54)
On Saturday 16 March 2013, Sebastian Hesselbarth wrote:
This driver adds a DT test clock consumer that exposes debugfs files to
enable/disable and set/get rate of the attached programmable clock.
During development of a i2c-attached clock generator I found it useful
to debug the clock generator's internal pll settings by enforcing clock
rates through debugfs.
Signed-off-by: Sebastian Hesselbarth<sebastian.hesselbarth@xxxxxxxxx>
It sounds a little clumsy to have a device driver to match a device that
you create just for matching the driver.
Would it be possible to separate the debugging logic from the platform
device logic? I think it may be useful to have a debugfs or sysfs
inteface for all clocks in the system, even if that is disabled by
default or only available after manually loading a module implementing
that functionality.
I agree that a generic approach is needed here. I have been meaning to
break the existing debugfs stuff out into clk-debug.c. I'll do that
soon and maybe you can add a new Kconfig entry for
COMMON_CLK_DEBUG_USERSPACE (or something like that) which implements
this?
Mike,
I agree with you and Arnd about clumsiness and a generic approach, but
this driver is a little different from controlling _all_ clocks within
the tree. It just adds one consumer that can _request_ a new rate.
Nevertheless, I can have a look at clk-debug and adding the functionality.
On the other hand this sort of stuff really scares me. I know for a
fact that a debug interface to enable/disable clocks and set clock rate
would ship on real devices. Quite likely some android phones out there
would be controlling hardware clocks from some horrible userspace
utility.
*shudder*
This will happen for sure.
Sebastian, another small nitpick, can you change the "enable" attribute
to be named "prepare_enable"? This more accurately reflects what is
going on.
On a generic approach I would rather have a look at the actual ops that
are provided and name the files accordingly. That will also allow us
_not_ to set the rate of crystal oscillators ;)
I also wonder how simple it would be to add a "parent" attribute here
that allows one to call clk_set_parent from the debugfs interface? To
make it easy on you, the interface could accept an integer as the index
of the clk->parents[] array. This is a bad interface design as it
requires the user to look into the code to know which index corresponds
to which parent clock; however I do not want people to use this
interface for anything other than debug/testing, so I am ok with this
interface being a PITA to use.
Sure, but it will not help much against userspace hardware clock
utilities ;)
Sebastian
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