Hi Elaine, On Wed, Mar 09, 2022 at 09:41:39AM +0800, zhangqing@xxxxxxxxxxxxxx wrote: > hi，all： > Let me explain the clock dependency： > From the clock tree, pclk_vo0 and hclk_vo0 are completely independent > clocks with different parent clocks and different clock frequencies。 > But the niu path is : > pclk_vo is dependent on hclk_vo, and the pclk_vo niu goes through hclk_vo > niu. Thanks, this is the information we are looking for. What is "NIU" btw? I think this is even documented in the Reference Manual. With the right pointer I just found: > A part of niu clocks have a dependence on another niu clock in order to > sharing the internal bus. When these clocks are in use, another niu > clock must be opened, and cannot be gated. These clocks and the special > clock on which they are relied are as following: > > Clocks which have dependency The clock which can not be gated > ----------------------------------------------------------------- > ... > pclk_vo_niu, hclk_vo_s_niu hclk_vo_niu > ... > The clock tree and NIU bus paths are designed independently > So there are three solutions to this problem: > 1. DTS adds a reference to Hclk while referencing Pclk. > 2, The dependent clock is always on, such as HCLK_VO0, but this is not > friendly for the system power. > 3. Create a non-clock-tree reference. Clk-link, for example, we have an > implementation in our internal branch, but Upstream is not sure how to > push it. I thought about something similar. That would help us here and on i.MX we have a similar situation: We have one bit that switches multiple clocks. That as well cannot be designed properly in the clock framework currently, but could be modelled with a concept of linked clocks. Doing this sounds like quite a bit of work and discussion though, I don't really like having this as a dependency to mainline the VOP2 driver. I vote for 1. in that case, we could still ignore the hclk in dts later when we have linked clocks. Sascha -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
