drm/i915: Fix possible int overflow in skl_ddi_calculate_wrpll()

On the off chance that clock value ends up being too high (by means
of skl_ddi_calculate_wrpll() having been called with big enough
value of crtc_state->port_clock * 1000), one possible consequence
may be that the result will not be able to fit into signed int.

Fix this issue by moving conversion of clock parameter from kHz to Hz
into the body of skl_ddi_calculate_wrpll(), as well as casting the
same parameter to u64 type while calculating the value for AFE clock.
This both mitigates the overflow problem and avoids possible erroneous
integer promotion mishaps.

Found by Linux Verification Center (linuxtesting.org) with static
analysis tool SVACE.

Fixes: 82d354370189 ("drm/i915/skl: Implementation of SKL DPLL programming")
Cc: stable@vger.kernel.org
Signed-off-by: Nikita Zhandarovich <n.zhandarovich@fintech.ru>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240729174035.25727-1-n.zhandarovich@fintech.ru

diff --git a/drivers/gpu/drm/i915/display/intel_dpll_mgr.c b/drivers/gpu/drm/i915/display/intel_dpll_mgr.c
index 90998b037349d398e338af5a1b01c2ec80d91186..292d163036b12a3817f77f40906854b729a42c92 100644 (file)
--- a/drivers/gpu/drm/i915/display/intel_dpll_mgr.c
+++ b/drivers/gpu/drm/i915/display/intel_dpll_mgr.c
@@ -1658,7 +1658,7 @@ static void skl_wrpll_params_populate(struct skl_wrpll_params *params,
 }
 
 static int
-skl_ddi_calculate_wrpll(int clock /* in Hz */,
+skl_ddi_calculate_wrpll(int clock,
                        int ref_clock,
                        struct skl_wrpll_params *wrpll_params)
 {
@@ -1683,7 +1683,7 @@ skl_ddi_calculate_wrpll(int clock /* in Hz */,
        };
        unsigned int dco, d, i;
        unsigned int p0, p1, p2;
-       u64 afe_clock = clock * 5; /* AFE Clock is 5x Pixel clock */
+       u64 afe_clock = (u64)clock * 1000 * 5; /* AFE Clock is 5x Pixel clock, in Hz */
 
        for (d = 0; d < ARRAY_SIZE(dividers); d++) {
                for (dco = 0; dco < ARRAY_SIZE(dco_central_freq); dco++) {
@@ -1808,7 +1808,7 @@ static int skl_ddi_hdmi_pll_dividers(struct intel_crtc_state *crtc_state)
        struct skl_wrpll_params wrpll_params = {};
        int ret;
 
-       ret = skl_ddi_calculate_wrpll(crtc_state->port_clock * 1000,
+       ret = skl_ddi_calculate_wrpll(crtc_state->port_clock,
                                      i915->display.dpll.ref_clks.nssc, &wrpll_params);
        if (ret)
                return ret;