Am Dienstag, den 24.11.2015, 15:35 +0800 schrieb Bai Ping: > > On 2015/11/23 17:40, Lucas Stach wrote: > > Am Montag, den 23.11.2015, 22:07 +0800 schrieb Bai Ping: > >> The i.MX7Dual/Solo is a new series of the i.MX SOC family. > >> The existing cpufreq driver for 'i.MX6' or 'cpufreq-dt' can > >> NOT match the requirement of this new SOC. This patch adds the > >> cpufreq driver for i.MX7Dual/Solo. > >> > > So, what are those requirements, which could not be matched with > > cpufreq-dt? We should really try to not add another cpufreq driver. > the requirement is the PLL1 used to source the CPU core clock can NOT > change frequency on the fly, > during the PLL1 frequency change, not clock output from this PLL1 in a > short time. this will lead to glitch > to the core clock. so before we change the PLL1's frequency, we must > switch the CPU core clock to another > clock source, after the PLL1 frequency has been changed, we switch back > core clock to PLL1. > > I don't see anything special in here. A single regulator and some clocks > > needing to be controlled in the right way. That's already handled for > > i.MX5 with cpufreq-dt. Please look up how it is done there and try to do > > it the same way for MX7, or provide substantial information why it > > couldn't be done. > I have checked the i.MX5 cpufreq, As on i.MX5, no need to take care of > the PLL's frequency change flow, > so the cpufreq-dt is the best one to support cpufreq. But on i.MX7, the > PLL design is not the same as on i.MX5, > additional steps needed in CPU frequency changing flow. the issue that > can NOT be tackled by cpufreq-dt is > additional step used by PLL frequency change.
This is wrong, we have the step clock requirement on MX5 as well, that's why I asked you to look into this. The MX5 clock controller provides a virtual ARM clock, that implements the proper clock switch flow. This allows to reuse cpufreq-dt, thus reducing code duplication in the cpufreq drivers greatly. Regards, Lucas -- Pengutronix e.K. | Lucas Stach | Industrial Linux Solutions | http://www.pengutronix.de/ | -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
