> -----Original Message----- > From: Kevin Hilman [mailto:khilman@xxxxxxxxxxxxxxxxxxx] > Sent: Tuesday, August 24, 2010 2:04 PM > > thara gopinath <thara@xxxxxx> writes: > > > From: Thara Gopinath <thara@xxxxxx> > > > > In the current opp layer the frequency matching API's > > tries to match the exact frequency passed in Hz. This leads > > to problems in cases where dplls are locked to slightly differnet > > frequencies due to sys clock speed or optimum M,N values. > > Consider the following scenario > > a. dpll_x is supposed to be locked at 266Mhz but is > > actually att 266.045 Mhz due to above mentioned reasons. > > b. The opp table has the entry as 266000000 hz. > > c. The user does a clk_get_rate(dpll_x) and passes the > > corresponding rate <rate> into the opp API's to get back > > a opp table entry. > > d. In this scenario if the user has called into > > opp_find_freq_exact it will return an error. > > If the user has called into opp_find_freq_ceil > > it will either return the opp entry corresponding > > to the next higher frequency in the opp table > > or return an error if 266 Mhz is the last entry > > in the table. > > > > The above is not correct as we expect the framework to return back > > the opp table entry corresponding to 266 Mhz. > > > > Now there are two ways of fixing this issue. > > a. Put the correct dpll lock frequency in the opp table. > > This means opp table will now have entries like 266045000 hz. > > But this is not scalable as these dpll lock frequencies > > can change slightly based on sys clk speeds. Like for eg > > at sys clk speed 38.4 Mhz we will able to get 266.045 Mhz > > where as at sys clk speed 26 Mhz we will be able to get > > onyl 266.124 Mhz etc. So depending on the platform we > > will have to start changing the opp table. > > > > b. Do the comparison in Mhz in the opp layer rather than in Hz. > > This would mean we will divide the rate passed into the opp layer > > API and the rates stored in the opp tables by 1000000 to get the > > rates in Mhz and do the necessary comparision. In this approach > any > > vague frequency like 266.045Mhz will get mapped to 266 Mhz in the > > opp table. But if the passed rate is 267 Mhz, the opp framework > > will still rerturn an error or the next highest opp table entry > > > > This patch implements solution b. The scenario mentioned above is > > esp true for OMAP4 dpll_iva where we do end up with such weird > frequencies > > due to sys clk being at 38.4 Mhz. > > I agree that solution b is better, although it makes the '_exact' > function a bit less exact. :/ > > solution b is fine with me, but the kerneldoc for these find functions > should be updated to describe the new matching technique. I agree, I suggest one improvement though - the search accuracy will vary Based on the silicon rev, one size will probably not fit every silicon and Domains we have - I suggest having accuracy as a parameter as part of domain Registration/configurable parameter e.g. > > + unsigned long rate = temp_opp->rate / 1000000; Will probably configurable to the "exactness" we expect to handle per domain/silicon family. > > Kevin > > > Signed-off-by: Thara Gopinath <thara@xxxxxx> > > --- > > arch/arm/plat-omap/opp.c | 37 ++++++++++++++++++++++++++----------- > > 1 files changed, 26 insertions(+), 11 deletions(-) > > > > diff --git a/arch/arm/plat-omap/opp.c b/arch/arm/plat-omap/opp.c > > index b9b7bda..ba7a554 100644 > > --- a/arch/arm/plat-omap/opp.c > > +++ b/arch/arm/plat-omap/opp.c > > @@ -212,15 +212,20 @@ struct omap_opp *opp_find_freq_exact(struct device > *dev, > > { > > struct device_opp *dev_opp; > > struct omap_opp *temp_opp, *opp = ERR_PTR(-ENODEV); > > + unsigned long req_freq = freq / 1000000; > > > > dev_opp = find_device_opp(dev); > > if (IS_ERR(dev_opp)) > > return opp; > > > > list_for_each_entry(temp_opp, &dev_opp->opp_list, node) { > > - if (temp_opp->enabled && temp_opp->rate == freq) { > > - opp = temp_opp; > > - break; > > + if (temp_opp->enabled) { > > + unsigned long rate = temp_opp->rate / 1000000; > > + > > + if (rate == req_freq) { > > + opp = temp_opp; > > + break; > > + } > > } > > } > > > > @@ -258,16 +263,21 @@ struct omap_opp *opp_find_freq_ceil(struct device > *dev, unsigned long *freq) > > { > > struct device_opp *dev_opp; > > struct omap_opp *temp_opp, *opp = ERR_PTR(-ENODEV); > > + unsigned long req_freq = *freq / 1000000; > > > > dev_opp = find_device_opp(dev); > > if (IS_ERR(dev_opp)) > > return opp; > > > > list_for_each_entry(temp_opp, &dev_opp->opp_list, node) { > > - if (temp_opp->enabled && temp_opp->rate >= *freq) { > > - opp = temp_opp; > > - *freq = opp->rate; > > - break; > > + if (temp_opp->enabled) { > > + unsigned long rate = temp_opp->rate / 1000000; > > + > > + if (rate >= req_freq) { > > + opp = temp_opp; > > + *freq = opp->rate; > > + break; > > + } > > } > > } > > > > @@ -305,16 +315,21 @@ struct omap_opp *opp_find_freq_floor(struct device > *dev, unsigned long *freq) > > { > > struct device_opp *dev_opp; > > struct omap_opp *temp_opp, *opp = ERR_PTR(-ENODEV); > > + unsigned long req_freq = *freq / 1000000; > > > > dev_opp = find_device_opp(dev); > > if (IS_ERR(dev_opp)) > > return opp; > > > > list_for_each_entry_reverse(temp_opp, &dev_opp->opp_list, node) { > > - if (temp_opp->enabled && temp_opp->rate <= *freq) { > > - opp = temp_opp; > > - *freq = opp->rate; > > - break; > > + if (temp_opp->enabled) { > > + unsigned long rate = temp_opp->rate / 1000000; > > + > > + if (rate <= req_freq) { > > + opp = temp_opp; > > + *freq = opp->rate; > > + break; > > + } > > } > > } Regards, Nishanth Menon -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
