If a clock has CLK_SET_RATE_PARENT, but core->parent is NULL (most
likely because it's orphan), callers of clk_core_init_rate_req() will
blindly call this function leading to a very verbose warning.

Since it's a fairly common situation, let's just remove the WARN_ON but
keep the check that prevents us from dereferencing the pointer.

Interestingly, it fixes a regression on the Mediatek MT8195 where the
GPU would stall during a clk_set_rate for its main clock. We couldn't
come up with a proper explanation since the condition is essentially the
same.

It was then assumed that it could be timing related since printing the
warning stacktrace takes a while, but we couldn't replicate the failure
by using fairly large (10ms) mdelays.

Fixes: 262ca38f4b6e ("clk: Stop forwarding clk_rate_requests to the parent")
Reported-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
---
 drivers/clk/clk.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index c3c3f8c07258..37d623c7b73b 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -1459,7 +1459,7 @@ static void clk_core_init_rate_req(struct clk_core * const core,
 {
 	struct clk_core *parent;
 
-	if (WARN_ON(!core || !req))
+	if (!core || WARN_ON(!req))
 		return;
 
 	memset(req, 0, sizeof(*req));

-- 
b4 0.11.0-dev-7da52

Quoting Maxime Ripard (2022-10-18 06:52:56)
> If a clock has CLK_SET_RATE_PARENT, but core->parent is NULL (most
> likely because it's orphan), callers of clk_core_init_rate_req() will
> blindly call this function leading to a very verbose warning.
> 
> Since it's a fairly common situation, let's just remove the WARN_ON but
> keep the check that prevents us from dereferencing the pointer.
> 
> Interestingly, it fixes a regression on the Mediatek MT8195 where the
> GPU would stall during a clk_set_rate for its main clock. We couldn't
> come up with a proper explanation since the condition is essentially the
> same.
> 
> It was then assumed that it could be timing related since printing the
> warning stacktrace takes a while, but we couldn't replicate the failure
> by using fairly large (10ms) mdelays.
> 
> Fixes: 262ca38f4b6e ("clk: Stop forwarding clk_rate_requests to the parent")
> Reported-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
> Signed-off-by: Maxime Ripard <maxime@cerno.tech>
> ---

Applied to clk-fixes

Il 18/10/22 15:52, Maxime Ripard ha scritto:
> If a clock has CLK_SET_RATE_PARENT, but core->parent is NULL (most
> likely because it's orphan), callers of clk_core_init_rate_req() will
> blindly call this function leading to a very verbose warning.
> 
> Since it's a fairly common situation, let's just remove the WARN_ON but
> keep the check that prevents us from dereferencing the pointer.
> 
> Interestingly, it fixes a regression on the Mediatek MT8195 where the
> GPU would stall during a clk_set_rate for its main clock. We couldn't
> come up with a proper explanation since the condition is essentially the
> same.
> 
> It was then assumed that it could be timing related since printing the
> warning stacktrace takes a while, but we couldn't replicate the failure
> by using fairly large (10ms) mdelays.
> 
> Fixes: 262ca38f4b6e ("clk: Stop forwarding clk_rate_requests to the parent")
> Reported-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
> Signed-off-by: Maxime Ripard <maxime@cerno.tech>

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>