Messages in this thread | | | Date | Tue, 19 Mar 2013 09:19:05 +0100 | From | Sebastian Hesselbarth <> | Subject | Re: [PATCH] clk: add DT test clock consumer driver |
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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@gmail.com> >> >> 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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