Messages in this thread | | | Date | Tue, 8 Oct 2013 10:27:44 -0500 | From | Felipe Balbi <> | Subject | Re: [RFC] clk: add flags to distinguish xtal clocks |
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Hi,
Fixing Luca's address since he left TI
On Mon, Oct 07, 2013 at 12:44:24AM -0700, Mike Turquette wrote: > Quoting Luciano Coelho (2013-07-29 06:50:42) > > Hi Mike, > > > > On Fri, 2013-07-05 at 10:54 +0300, Luciano Coelho wrote: > > > On Thu, 2013-07-04 at 16:19 -0700, Mike Turquette wrote: > > > > Quoting Luciano Coelho (2013-07-04 15:37:45) > > > > > On Thu, 2013-07-04 at 15:25 -0700, Mike Turquette wrote: > > > > > > Or is it the same clock input and basically the problem is that you need > > > > > > to know what kind of waveform to expect (e.g. square versus sine)? > > > > > > > > > > It's the same clock input in the chip's perspective. One clock input > > > > > that can be any of the combinations I mentioned above. Again, I'm not > > > > > familiar with clocks, so I guess the square vs. sine explanation is > > > > > plausible. What I could see in the firmware is that it handles the > > > > > clocks differently if they're xtal or not. > > > > > > > > OMAP has a similar thing where sys_clkin (the fast reference clock for > > > > the chip) can be 19.2, 26, 38.4, etc. This is easy to handle since only > > > > the rates matter. > > > > > > Right, this part is easy and I already have the code for that. What I'm > > > missing is a way to pass this XTAL flag to the chip. > > > > > > > > > > In your case you need some extra metadata to know what to do. I'm really > > > > not sure if CLK_IS_TYPE_XTAL is the most useful form this metadata can > > > > take. It would be best to know if the waveform is what you really need > > > > to know, or perhaps something else. For instance you might be affected > > > > by some clock signal stabilization time. Can you talk to your hardware > > > > guys and figure it out? I'd rather model the actual needs instead of > > > > just tossing a flag in there. > > > > > > I get your point. I have tried to investigate how this flag is used by > > > the firmware and I could see that it is used to set different "buffer > > > gains" and "delays" when waking up (I guess this means when the clock is > > > starting, so probably related to stabilization time). They specify two > > > "modes", "boost" and "normal" and use different delay values for each. > > > > I tried but I couldn't find any more information on how exactly this > > works. But since this change is really simple and there seems to be > > other people who need the same information, couldn't we add it as is and > > try to figure out more specific information about the clocks later on? > > > > Even if XTAL is not that useful if we know the other details, at least > > it wouldn't hurt to have the flag there anyway. > > Luca, > > By any chance did you come to a different solution for this problem? I > can take the patch, but I do not feel like we're solving the right > problem the right way. > > If not I will take it for 3.13. > > Regards, > Mike > > > > > -- > > Cheers, > > Luca.
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