When the MFG PLL clock, which is upstream of the MFG clock, is changed, the downstream clock and consumers need to be switched away from the PLL over to a stable clock to avoid glitches. This is done through the use of the newly added clk mux notifier. The notifier is set on the mux itself instead of the upstream PLL, but in practice this works, as the rate change notifitcations are propogated throughout the sub-tree hanging off the PLL. Just before rate changes, the MFG mux is temporarily and transparently switched to the 26 MHz main crystal. After the rate change, the mux is switched back. Signed-off-by: Chen-Yu Tsai <wenst@chromium.org> [Angelo: Rebased to assign clk_ops in mtk_mux_nb] Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com> Reviewed-by: Miles Chen <miles.chen@mediatek.com> Link: https://lore.kernel.org/r/20220927101128.44758-5-angelogioacchino.delregno@collabora.com Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>