[PATCH] drm/i915: rework the error handling in *_dpll_params

From: trix
Date: Fri Mar 04 2022 - 16:04:15 EST


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.

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