On Tue, Dec 18, 2012 at 4:19 AM, Sascha Hauer <s.ha...@pengutronix.de> wrote: > On Thu, Dec 06, 2012 at 10:52:03AM +0800, Chao Xie wrote: >> hi >> When develop the clk drivers for SOCs based on common clock framework. >> I met a issue. >> For example there is a uart device, it's function clock comes from a >> divider, and the divider's parent is a mux. It means >> >> MUX --> DIV --> UART >> >> As we know that UART can work at low baudrate for a terminal, while it >> can also connect to GPS module which needs a high rate. So the MUX >> will provide two clock source, a low clock rate and high clock rate. >> >> The MUX clk driver clk-mux.c does not implement a ->round_rate callbacks. >> It means that when uart driver is used for a GPS and it want to change >> it clock, the driver will call clk_set_rate(); clk_set_rate will loop >> upward to DIV, and DIV will try to set its divider, and it need loop >> upward to MUX. >> In fact the current clk drivers have some issue. >> MUX clk driver should provide the round_rate callback, it then can >> provide a new_rate. It means that in clk_calc_subtree MUX can switch >> the clock source. > > It's not that simple. The input clocks to a mux may not only differ in > their rate but can also have other different properties, like for > example one input may be always present whereas another input only runs > when the CPU is in run mode. > > It may be a possibility to add a flag to the mux to explicitely > allow reparenting on a rate change. > > Sascha > > -- > Pengutronix e.K. | | > Industrial Linux Solutions | http://www.pengutronix.de/ | > Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | > Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-555
There is already a flag to do it. CLK_SET_RATE_PARENT if the mux does not want to changes the input for clk_set_rate called by its child, it can clear this flag. The question is whether we need add the round_rate/recalc_rate for MUX type of clock? Is there any special issue about it that why current MUX implementation does not have these callbacks? -- 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/