linux-kernel - Re: [PATCH v3] clk: core: Honor CLK_OPS_PARENT_ENABLE in clk_core_is

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Date:   Tue, 3 Jan 2023 12:53:04 +0100
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Chen-Yu Tsai <wenst@...omium.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>
Cc:     Nícolas F . R . A . Prado 
        <nfraprado@...labora.com>,
        Alexander Stein <alexander.stein@...tq-group.com>,
        Marcel Ziswiler <marcel.ziswiler@...adex.com>,
        linux-clk@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] clk: core: Honor CLK_OPS_PARENT_ENABLE in
 clk_core_is_enabled

Il 03/01/23 10:23, Chen-Yu Tsai ha scritto:
> In the previous commits that added CLK_OPS_PARENT_ENABLE, support for
> this flag was only added to rate change operations (rate setting and
> reparent) and disabling unused subtree. It was not added to the
> clock gate related operations. Any hardware driver that needs it for
> these operations will either see bogus results, or worse, hang.
> 
> This has been seen on MT8192 and MT8195, where the imp_ii2_* clk
> drivers set this, but dumping debugfs clk_summary would cause it
> to hang.
> 
> Prepare parent on prepare and enable parent on enable dependencies are
> already handled automatically by the core as part of its sequencing.
> Whether the case for "enable parent on prepare" should be supported by
> this flag or not is not clear, and thus ignored for now.
> 
> This change solely fixes the handling of clk_core_is_enabled, i.e.
> enabling the parent clock when reading the hardware state. Unfortunately
> clk_core_is_enabled is called in a variety of places, sometimes with
> the enable clock already held. To avoid deadlocking, the core will
> ignore readouts and just return false if CLK_OPS_PARENT_ENABLE is set
> but the parent isn't currently enabled.
> 
> Fixes: fc8726a2c021 ("clk: core: support clocks which requires parents enable (part 2)")
> Fixes: a4b3518d146f ("clk: core: support clocks which requires parents enable (part 1)")
> Signed-off-by: Chen-Yu Tsai <wenst@...omium.org>

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

Moreover, for MT6795 Xperia M5, MT8173 Elm, MT8192 Asurada, MT8195 Tomato:

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