Quoting AngeloGioacchino Del Regno (2021-01-13 10:38:13) > The function clk_gfx3d_determine_rate is selecting different PLLs > to manage the GFX3D clock source in a special way: this one needs > to be ping-pong'ed on different PLLs to ensure stability during > frequency switching (set a PLL rate, let it stabilize, switch the > RCG to the new PLL) and fast frequency transitions. > > This technique is currently being used in the MSM8996 SoC and the > function was assuming that the parents were always at a specific > index in the parents list, which is TRUE, if we use this only on > the MSM8996 MMCC. > Unfortunately, MSM8996 is not the only SoC that needs to ping-pong > the graphics RCG, so choices are: > 1. Make new special ops just to hardcode *again* other indexes, > creating code duplication for (imo) no reason; or > 2. Generalize this function, so that it becomes usable for a range > of SoCs with slightly different ping-pong configuration. > > In this commit, the second road was taken: define a new "special" > struct clk_rcg2_gfx3d, containing the ordered list of parents to > ping-pong the graphics clock on, and the "regular" rcg2 clock > structure in order to generalize the clk_gfx3d_determine_rate > function and make it working for other SoCs. > > As for the function itself it is left with the assumption that we > need to ping-pong over three parents. The reasons for this are: > 1. The initial model was MSM8996, which has 3 parents for the > graphics clock pingpong; > 2. The other example that was taken into consideration is the > SDM630/636/660 SoC gpu clock controller, which is ping-ponging > over two dynamic clocked and one fixed clock PLL. > > Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxxx> > --- Applied to clk-next but I modified it a bunch. Let me know if it doesn't work.
