The calculated ideal rate can easily overflow an unsigned long, thus
making the best div selection buggy as soon as no ideal match is found
before the overflow occurs.
Fixes: 4731a72df273 ("drm/sun4i: request exact rates to our parents")
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxx>
Acked-by: Maxime Ripard <maxime.ripard@xxxxxxxxxxx>
---
Changes in v2:
- Add a comment to explain why we bail out after an overflow
- Add Maxime ack
- Use a goto instead of a break
---
drivers/gpu/drm/sun4i/sun4i_dotclock.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/sun4i/sun4i_dotclock.c b/drivers/gpu/drm/sun4i/sun4i_dotclock.c
index e36004fbe453..2a15f2f9271e 100644
--- a/drivers/gpu/drm/sun4i/sun4i_dotclock.c
+++ b/drivers/gpu/drm/sun4i/sun4i_dotclock.c
@@ -81,9 +81,19 @@ static long sun4i_dclk_round_rate(struct clk_hw *hw, unsigned long rate,
int i;
for (i = tcon->dclk_min_div; i <= tcon->dclk_max_div; i++) {
- unsigned long ideal = rate * i;
+ u64 ideal = (u64)rate * i;
unsigned long rounded;
+ /*
+ * ideal has overflowed the max value that can be stored in an
+ * unsigned long, and every clk operation we might do on a
+ * truncated u64 value will give us incorrect results.
+ * Let's just stop there since bigger dividers will result in
+ * the same overflow issue.
+ */
+ if (ideal > ULONG_MAX)
+ goto out;
+
rounded = clk_hw_round_rate(clk_hw_get_parent(hw),
ideal);
--
2.14.1
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