linux-kernel - Re: [PATCH 1/4] clk: Remove WARN_ON NULL parent in clk_core_init_rate

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Message-ID: <c196afc4-46e8-a61a-b0fe-c92f26614a8f@collabora.com>
Date:   Tue, 18 Oct 2022 16:35:04 +0200
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Maxime Ripard <maxime@...no.tech>, Stephen Boyd <sboyd@...nel.org>,
        Michael Turquette <mturquette@...libre.com>
Cc:     linux-kernel@...r.kernel.org, linux-clk@...r.kernel.org
Subject: Re: [PATCH 1/4] clk: Remove WARN_ON NULL parent in
 clk_core_init_rate_req()

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@...labora.com>
> Signed-off-by: Maxime Ripard <maxime@...no.tech>

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