On 16.05.2014 16:35, Rahul Sharma wrote: > On 16 May 2014 16:22, Tomasz Figa <t.figa@xxxxxxxxxxx> wrote: >> Hi Rahul, >> >> On 16.05.2014 12:39, Rahul Sharma wrote: >>> [snip] >>>> + gate->lock = &clkout_lock; >>>> + >>>> + mux->reg = reg + EXYNOS_PMU_DEBUG_REG; >>>> + mux->mask = EXYNOS_CLKOUT_MUX_MASK; >>>> + mux->shift = EXYNOS_CLKOUT_MUX_SHIFT; >>>> + mux->lock = &clkout_lock; >>>> + >>>> + clk = clk_register_composite(NULL, "clkout", parent_names, >>>> + parent_count, &mux->hw, >>>> + &clk_mux_ops, NULL, NULL, &gate->hw, >>>> + &clk_gate_ops, 0); >>>> + if (IS_ERR(clk)) >>>> + goto err_unmap; >>>> + >>> >>> Hi Tomasz, >>> >>> Do we really need a composite clock here? How about registering >>> a mux and a gate separately? >> >> What's wrong with a composite clock? It simplifies the code as just a >> single clock needs to be registered. I don't see any drawbacks compared >> to registering two clocks separately. >> > > I always took it as a thumb rule to not to use composite clocks if you > can easily represent the block using basic clocks structures. > > There can be a problem when drivers using such clocks assume that such > clock continue to offer composite functionality for all futures SoCs and > write code around it. This is what we faced when fixing drivers during > CCF migration. The drivers using CLKOUT need to be designed this way, because they are not Exynos-specific, such as drivers for HSIC hubs or audio codecs. They can't have any Exynos-specific knowledge about clock hierarchy. So regardless of whether this is implemented using the composite clock or not, consumer device drivers need to be able to use just a single clock to do whatever they need, e.g. gating or rate configuration. However I can see one problem here with my implementation - it is missing the CLK_SET_RATE_PARENT flag, so dividers of particular CLK_OUTs from CMU blocks could be reconfigured. Also the driver is missing save and restore of PMU_DEBUG register. I will fix both in next version. Best regards, Tomasz -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
