Re: [PATCH v5 02/10] phy: rockchip: samsung-hdptx: Prevent divide-by-zero when computing clk rate

[Manivannan Sadhasivam]

On Thu, Jul 23, 2026 at 10:41:45PM +0300, Cristian Ciocaltea wrote:
> 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 <sashiko-bot@xxxxxxxxxx>
> Closes: https://sashiko.dev/#/patchset/20260611-hdptx-clk-fixes-v3-0-67b1b0c00e16@xxxxxxxxxxxxx?part=1
> Fixes: 3481fc04d969 ("phy: rockchip: samsung-hdptx: Compute clk rate from PLL config")
> Tested-by: Diederik de Haas <diederik@xxxxxxxxxxxxxx>  # NanoPC-T6 LTS
> Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxxxxxxxx>
> Reviewed-by: Andy Yan <andy.yan@xxxxxxxxxxxxxx>
> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@xxxxxxxxxxxxx>
> ---
>  drivers/phy/rockchip/phy-rockchip-samsung-hdptx.c | 11 ++++++++---
>  1 file changed, 8 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..44e99343f249 100644
> --- a/drivers/phy/rockchip/phy-rockchip-samsung-hdptx.c
> +++ b/drivers/phy/rockchip/phy-rockchip-samsung-hdptx.c
> @@ -2270,10 +2270,15 @@ 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) {
> +			dev_dbg(hdptx->dev, "Invalid ROPLL hw state: deno == 0\n");

If the hardware state is invalid, why can't this be a hard failure?

- Mani

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