[PATCH v6 02/10] phy: rockchip: samsung-hdptx: Prevent divide-by-zero when computing clk rate

Calculating 'sdm' fraction in rk_hdptx_phy_clk_calc_rate_from_pll_cfg()
could trigger a divide-by-zero, as it uses div_u64() with a denominator
read directly from hardware: the values ropll_hw.sdm_deno,
ropll_hw.sdc_deno, ropll_hw.sdc_n, and ropll_hw.sdc_num are populated
from PLL registers which, in theory, could be left by the bootloader
uninitialized/misconfigured.

Provide the necessary sanitization to avoid trusting the hardware state.

Reported-by: Sashiko <[email protected]>
Closes: https://sashiko.dev/#/patchset/[email protected]?part=1
Fixes: 3481fc04d969 ("phy: rockchip: samsung-hdptx: Compute clk rate from PLL config")
Tested-by: Diederik de Haas <[email protected]>  # NanoPC-T6 LTS
Reviewed-by: Dmitry Baryshkov <[email protected]>
Reviewed-by: Andy Yan <[email protected]>
Signed-off-by: Cristian Ciocaltea <[email protected]>
---
 drivers/phy/rockchip/phy-rockchip-samsung-hdptx.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/drivers/phy/rockchip/phy-rockchip-samsung-hdptx.c b/drivers/phy/rockchip/phy-rockchip-samsung-hdptx.c
index 710603afff86..d67ced2bf7b2 100644
--- a/drivers/phy/rockchip/phy-rockchip-samsung-hdptx.c
+++ b/drivers/phy/rockchip/phy-rockchip-samsung-hdptx.c
@@ -2270,10 +2270,20 @@ static u64 rk_hdptx_phy_clk_calc_rate_from_pll_cfg(struct rk_hdptx_phy *hdptx)
 
 	fout = PLL_REF_CLK * ropll_hw.pms_mdiv;
 	if (ropll_hw.sdm_en) {
+		val = 16U * ropll_hw.sdm_deno *
+		      (ropll_hw.sdc_deno * ropll_hw.sdc_n - ropll_hw.sdc_num);
+		if (!val) {
+			/*
+			 * The PLL config currently stored in hardware can't be
+			 * translated into a rate. The next .set_rate() should
+			 * program a valid configuration and help with recovery.
+			 */
+			dev_dbg(hdptx->dev, "Invalid ROPLL hw state: deno == 0\n");
+			return 0;
+		}
+
 		sdm = div_u64(PLL_REF_CLK * ropll_hw.sdc_deno *
-			      ropll_hw.pms_mdiv * ropll_hw.sdm_num,
-			      16 * ropll_hw.sdm_deno *
-			      (ropll_hw.sdc_deno * ropll_hw.sdc_n - ropll_hw.sdc_num));
+			      ropll_hw.pms_mdiv * ropll_hw.sdm_num, val);
 
 		if (ropll_hw.sdm_num_sign)
 			fout = fout - sdm;

-- 
2.55.0


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