From: Adam Ford aford173@gmail.com
[ Upstream commit 8208181fe536bba3b411508f81c4426fc9c71d9a ]
Currently, certain clocks are derrived as a divider from their parent clock. For some clocks, even when CLK_SET_RATE_PARENT is set, the parent clock is not properly set which can lead to some relatively inaccurate clock values.
Unlike imx/clk-composite-93 and imx/clk-divider-gate, it cannot rely on calling a standard determine_rate function, because the 8m composite clocks have a pre-divider and post-divider. Because of this, a custom determine_rate function is necessary to determine the maximum clock division which is equivalent to pre-divider * the post-divider.
With this added, the system can attempt to adjust the parent rate when the proper flags are set which can lead to a more precise clock value.
On the imx8mplus, no clock changes are present. On the Mini and Nano, this can help achieve more accurate lcdif clocks. When trying to get a pixel clock of 31.500MHz on an imx8m Nano, the clocks divided the 594MHz down, but left the parent rate untouched which caused a calulation error.
Before: video_pll 594000000 video_pll_bypass 594000000 video_pll_out 594000000 disp_pixel 31263158 disp_pixel_clk 31263158
Variance = -236842 Hz
After this patch: video_pll 31500000 video_pll_bypass 31500000 video_pll_out 31500000 disp_pixel 31500000 disp_pixel_clk 31500000
Variance = 0 Hz
All other clocks rates and parent were the same. Similar results on imx8mm were found.
Fixes: 690dccc4a0bf ("Revert "clk: imx: composite-8m: Add support to determine_rate"") Signed-off-by: Adam Ford aford173@gmail.com Reviewed-by: Abel Vesa abel.vesa@linaro.org Tested-by: Fabio Estevam festevam@gmail.com Link: https://lore.kernel.org/r/20230506195325.876871-1-aford173@gmail.com Signed-off-by: Abel Vesa abel.vesa@linaro.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/clk/imx/clk-composite-8m.c | 31 ++++++++++++++++++++++++++++++ 1 file changed, 31 insertions(+)
diff --git a/drivers/clk/imx/clk-composite-8m.c b/drivers/clk/imx/clk-composite-8m.c index cbf0d7955a00a..7a6e3ce97133b 100644 --- a/drivers/clk/imx/clk-composite-8m.c +++ b/drivers/clk/imx/clk-composite-8m.c @@ -119,10 +119,41 @@ static int imx8m_clk_composite_divider_set_rate(struct clk_hw *hw, return ret; }
+static int imx8m_divider_determine_rate(struct clk_hw *hw, + struct clk_rate_request *req) +{ + struct clk_divider *divider = to_clk_divider(hw); + int prediv_value; + int div_value; + + /* if read only, just return current value */ + if (divider->flags & CLK_DIVIDER_READ_ONLY) { + u32 val; + + val = readl(divider->reg); + prediv_value = val >> divider->shift; + prediv_value &= clk_div_mask(divider->width); + prediv_value++; + + div_value = val >> PCG_DIV_SHIFT; + div_value &= clk_div_mask(PCG_DIV_WIDTH); + div_value++; + + return divider_ro_determine_rate(hw, req, divider->table, + PCG_PREDIV_WIDTH + PCG_DIV_WIDTH, + divider->flags, prediv_value * div_value); + } + + return divider_determine_rate(hw, req, divider->table, + PCG_PREDIV_WIDTH + PCG_DIV_WIDTH, + divider->flags); +} + static const struct clk_ops imx8m_clk_composite_divider_ops = { .recalc_rate = imx8m_clk_composite_divider_recalc_rate, .round_rate = imx8m_clk_composite_divider_round_rate, .set_rate = imx8m_clk_composite_divider_set_rate, + .determine_rate = imx8m_divider_determine_rate, };
static u8 imx8m_clk_composite_mux_get_parent(struct clk_hw *hw)