On Fri, Mar 04, 2022 at 01:03:55PM -0800, trix@xxxxxxxxxx wrote:
> From: Tom Rix <trix@xxxxxxxxxx>
>
> Clang static analysis reports this issue
> intel_dpll.c:472:31: warning: The left operand of '-'
> is a garbage value [core.UndefinedBinaryOperatorResult]
> this_err = abs(clock.dot - target);
> ~~~~~~~~~ ^
>
> In a loop clock.dot is set on successful call to
> i9xx_calc_dpll_params(). If the call fails, the later
> *is_valid() will use the previous loop's clock.dot.
I don't think this can happen. intel_pll_is_valid() validates
all the dividers first and bails out if they are junk.
>
> The *_dpll_params functions return an arithmetic statement
> with the clock.dot as the variable. Change the error handler
> to set clock.dot to 0 and jump to the return statement.
>
> Fixes: dccbea3b0704 ("drm/i915: calculate the port clock rate along with other PLL params")
> Signed-off-by: Tom Rix <trix@xxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/display/intel_dpll.c | 32 ++++++++++++++---------
> 1 file changed, 20 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dpll.c b/drivers/gpu/drm/i915/display/intel_dpll.c
> index 0ae37fdbf2a5b..ba7cada704288 100644
> --- a/drivers/gpu/drm/i915/display/intel_dpll.c
> +++ b/drivers/gpu/drm/i915/display/intel_dpll.c
> @@ -309,11 +309,13 @@ int pnv_calc_dpll_params(int refclk, struct dpll *clock)
> {
> clock->m = clock->m2 + 2;
> clock->p = clock->p1 * clock->p2;
> - if (WARN_ON(clock->n == 0 || clock->p == 0))
> - return 0;
> + if (WARN_ON(clock->n == 0 || clock->p == 0)) {
> + clock->dot = 0;
> + goto end;
> + }
> clock->vco = DIV_ROUND_CLOSEST(refclk * clock->m, clock->n);
> clock->dot = DIV_ROUND_CLOSEST(clock->vco, clock->p);
> -
> +end:
> return clock->dot;
> }
>
> @@ -326,11 +328,13 @@ int i9xx_calc_dpll_params(int refclk, struct dpll *clock)
> {
> clock->m = i9xx_dpll_compute_m(clock);
> clock->p = clock->p1 * clock->p2;
> - if (WARN_ON(clock->n + 2 == 0 || clock->p == 0))
> - return 0;
> + if (WARN_ON(clock->n + 2 == 0 || clock->p == 0)) {
> + clock->dot = 0;
> + goto end;
> + }
> clock->vco = DIV_ROUND_CLOSEST(refclk * clock->m, clock->n + 2);
> clock->dot = DIV_ROUND_CLOSEST(clock->vco, clock->p);
> -
> +end:
> return clock->dot;
> }
>
> @@ -338,11 +342,13 @@ int vlv_calc_dpll_params(int refclk, struct dpll *clock)
> {
> clock->m = clock->m1 * clock->m2;
> clock->p = clock->p1 * clock->p2;
> - if (WARN_ON(clock->n == 0 || clock->p == 0))
> - return 0;
> + if (WARN_ON(clock->n == 0 || clock->p == 0)) {
> + clock->dot = 0;
> + goto end;
> + }
> clock->vco = DIV_ROUND_CLOSEST(refclk * clock->m, clock->n);
> clock->dot = DIV_ROUND_CLOSEST(clock->vco, clock->p);
> -
> +end:
> return clock->dot / 5;
> }
>
> @@ -350,12 +356,14 @@ int chv_calc_dpll_params(int refclk, struct dpll *clock)
> {
> clock->m = clock->m1 * clock->m2;
> clock->p = clock->p1 * clock->p2;
> - if (WARN_ON(clock->n == 0 || clock->p == 0))
> - return 0;
> + if (WARN_ON(clock->n == 0 || clock->p == 0)) {
> + clock->dot = 0;
> + goto end;
> + }
> clock->vco = DIV_ROUND_CLOSEST_ULL(mul_u32_u32(refclk, clock->m),
> clock->n << 22);
> clock->dot = DIV_ROUND_CLOSEST(clock->vco, clock->p);
> -
> +end:
> return clock->dot / 5;
> }
>
> --
> 2.26.3
--
Ville Syrjälä
Intel
