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Message-ID: <34b7503e-5d1e-4fd2-a909-d7f50e45c8e6@baylibre.com>
Date:   Mon, 6 Nov 2023 09:50:29 +0100
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Subject: Re: [PATCH v3 3/3] clk: mediatek: mt8188-topckgen: Refactor parents
 for top_dp/edp muxes
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>, sboyd@kernel.org
Cc:     mturquette@baylibre.com, matthias.bgg@gmail.com,
        wenst@chromium.org, msp@baylibre.com, yangyingliang@huawei.com,
        u.kleine-koenig@pengutronix.de, linux-clk@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org, kernel@collabora.com
References: <20231103102533.69280-1-angelogioacchino.delregno@collabora.com>
 <20231103102533.69280-4-angelogioacchino.delregno@collabora.com>
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From:   Alexandre Mergnat <amergnat@baylibre.com>
In-Reply-To: <20231103102533.69280-4-angelogioacchino.delregno@collabora.com>
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On 03/11/2023 11:25, AngeloGioacchino Del Regno wrote:
> The top_dp and top_edp muxes can be both parented to either TVDPLL1
> or TVDPLL2, two identically specced PLLs for the specific purpose of
> giving out pixel clock: this becomes a problem when the MediaTek
> DisplayPort Interface (DPI) driver tries to set the pixel clock rate.
> 
> In the usecase of two simultaneous outputs (using two controllers),
> it was seen that one of the displays would sometimes display garbled
> output (if any at all) and this was because:
>   - top_edp was set to TVDPLL1, outputting X GHz
>   - top_dp was set to TVDPLL2, outputting Y GHz
>     - mtk_dpi calls clk_set_rate(top_edp, Z GHz)
>   - top_dp is switched to TVDPLL1
>   - TVDPLL1 changes its rate, top_edp outputs the wrong rate.
>   - eDP display is garbled
> 
> To solve this issue, remove all TVDPLL1 parents from `top_dp` and
> all TVDPLL2 parents from `top_edp`, plus, necessarily switch both
> clocks to use the new MUX_GATE_CLR_SET_UPD_INDEXED() macro to be
> able to use the right bit index for the new parents list.

Reviewed-by: Alexandre Mergnat <amergnat@baylibre.com>

-- 
Regards,
Alexandre