Messages in this thread | | | Date | Wed, 27 Mar 2013 12:09:17 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [PATCH v4] clk: allow reentrant calls into the clk framework |
| |
On Wed, 27 Mar 2013, Ulf Hansson wrote: > On 27 March 2013 10:55, Viresh Kumar <viresh.kumar@linaro.org> wrote: > > On 27 March 2013 15:10, Thomas Gleixner <tglx@linutronix.de> wrote: > >> On Wed, 27 Mar 2013, Mike Turquette wrote: > >> > >>> Reentrancy into the clock framework from the clk.h api is necessary > >>> for clocks that are prepared and unprepared via i2c_transfer (which > >>> includes many PMICs and discrete audio chips) as well as for several > >>> other use cases. > >> > >> That explanation sucks. > >> > >> Why does an i2c clock need reentrancy? Just because it's i2c or what? > > > > I am noway connected to this development but was just going through > > your mail and i think i might know the answer why is this required. > > > > Consider an example where an external chip has clock controller and has > > bits which can be programmed to enable/disable clock. And this chip is > > connected via spi/i2c to SoC. > > > > clk_prepare(peripheral on external chip) > > -> i2c_xfer(to write to external chips register) > > -> clk_enable(i2c controller) > > ->controller-xfer-routine.. and finally we enable clk here...
Which does not explain the whole issue:
clk_prepare() takes the mutex clk_enable() takes the spinlock
That works today.
The issue arises, if you need to call clk_prepare(i2c) in the xfer routine.
> > > > Sorry if i am on the wrong side :)
Only slightly :)
> I agree with you Viresh. I guess Mike should update the commit message. > > I would also like add another reason to why this is needed. For some > clks you would like to do pinctrl operations from a clk hw. But since > a pinctrl driver likely requires a clk to be prepared|enabled, we run > into a clk reentrant issue.
Fair enough. This all wants to go into the changelog, so we can understand why we have this business.
Thanks,
tglx
| |