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Date:   Tue, 1 Aug 2023 21:45:16 +0200
From:   Marco Felsch <m.felsch@pengutronix.de>
To:     Ahmad Fatoum <a.fatoum@pengutronix.de>
Cc:     Abel Vesa <abelvesa@kernel.org>, Peng Fan <peng.fan@nxp.com>,
        Michael Turquette <mturquette@baylibre.com>,
        Stephen Boyd <sboyd@kernel.org>,
        Shawn Guo <shawnguo@kernel.org>,
        Sascha Hauer <s.hauer@pengutronix.de>,
        Pengutronix Kernel Team <kernel@pengutronix.de>,
        Fabio Estevam <festevam@gmail.com>,
        NXP Linux Team <linux-imx@nxp.com>,
        linux-clk@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] clk: imx: composite-8m: avoid glitches when set_rate
 would be a no-op
Message-ID: <20230801194516.h6gxj2lqmmmls62k@pengutronix.de>
References: <20230801162731.3278396-1-a.fatoum@pengutronix.de>
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On 23-08-01, Ahmad Fatoum wrote:
> Reconfiguring the clock divider to the exact same value is observed
> on an i.MX8MN to often cause a short clock pause, probably because
> the divider restarts counting from the time the register is written.
> 
> This issue doesn't show up normally, because the clock framework will
> take care to not call set_rate when the clock rate is the same.
> However, when we configure an upstream clock (e.g. an audio_pll), the
> common code will call set_rate with the newly calculated rate on all
> children. As the new rate is different, we enter set_rate and compute
> the same divider values, write them back and cause the glitch (e.g.
> on a SAI's MCLK).
> 
> To avoid the glitch, we skip writing the same value back again.
> 
> Fixes: d3ff9728134e ("clk: imx: Add imx composite clock")
> Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>

Reviewed-by: Marco Felsch <m.felsch@pengutronix.de>