From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from metis.whiteo.stw.pengutronix.de (metis.whiteo.stw.pengutronix.de [185.203.201.7]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D8F0A1D5178 for ; Tue, 11 Feb 2025 07:47:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.203.201.7 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739260060; cv=none; b=A3dzORZdxxt6SFb6Bx5gPlyVjhVsfzR+zO5Rm/c65ij9DmZghvMWy7g1HEgv4ngDcRQGoZZvVXnA43Hi62koysGd9iKEcr+S68ennk9HnQb9rgvkcbyY5+95uaPde3/Y8n7Jqb4JuiAIqSkGLL+FCc9hJWflmo8+uXZk+VOti3w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739260060; c=relaxed/simple; bh=bszsusd0ALXbiJ8cte6QhE6oJEsnWRz1Y0Gw+xAdlWI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=GGkwvFgLT4hI+4FeOhESskZRWPyBJq4IEKCFVORAu6UJg4sgK+xMoTr/hskv3GHEJsV/kgtinY72yvaSvX/c/ZDyqKhULGiO4dv8vX6Qquod1NtI3QMk312/Is6SAG808vcUdN4fBOEXk5mbxLmmllzu6wHIba5dEWlRZOtoHXg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=pengutronix.de; spf=pass smtp.mailfrom=pengutronix.de; arc=none smtp.client-ip=185.203.201.7 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=pengutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=pengutronix.de Received: from drehscheibe.grey.stw.pengutronix.de ([2a0a:edc0:0:c01:1d::a2]) by metis.whiteo.stw.pengutronix.de with esmtps (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1thkzF-0007Hw-1Z; Tue, 11 Feb 2025 08:47:17 +0100 Received: from pty.whiteo.stw.pengutronix.de ([2a0a:edc0:2:b01:1d::c5]) by drehscheibe.grey.stw.pengutronix.de with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.96) (envelope-from ) id 1thkzE-000NbY-1A; Tue, 11 Feb 2025 08:47:16 +0100 Received: from sha by pty.whiteo.stw.pengutronix.de with local (Exim 4.96) (envelope-from ) id 1thkzE-0094Je-0o; Tue, 11 Feb 2025 08:47:16 +0100 Date: Tue, 11 Feb 2025 08:47:16 +0100 From: Sascha Hauer To: Alexander Stein Cc: Abel Vesa , Peng Fan , Michael Turquette , Stephen Boyd , Shawn Guo , Pengutronix Kernel Team , Fabio Estevam , linux-clk@vger.kernel.org, imx@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 3/3] clk: imx: clk-fracn-gppll: Support dynamic rates Message-ID: References: <20250210160012.783446-1-alexander.stein@ew.tq-group.com> <20250210160012.783446-3-alexander.stein@ew.tq-group.com> Precedence: bulk X-Mailing-List: imx@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250210160012.783446-3-alexander.stein@ew.tq-group.com> X-Sent-From: Pengutronix Hildesheim X-URL: http://www.pengutronix.de/ X-Accept-Language: de,en X-Accept-Content-Type: text/plain X-SA-Exim-Connect-IP: 2a0a:edc0:0:c01:1d::a2 X-SA-Exim-Mail-From: sha@pengutronix.de X-SA-Exim-Scanned: No (on metis.whiteo.stw.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: imx@lists.linux.dev Hi Alexander, On Mon, Feb 10, 2025 at 05:00:11PM +0100, Alexander Stein wrote: > The fracn gppll PLL so far only supports rates from a rate table passed > during initialization. Calculating PLL settings dynamically helps audio > applications to get their desired rates, so support for this is added > in this patch. > > The strategy to get to the PLL setting for a rate is: > > - The rate table is searched for suitable rates, so for standard rates the > same settings are used as without this patch > - Then try to only adjust mfn, on fractional PLLs only, which specifies > the fractional part of the PLL. This setting can be changed without > glitches on the output and is therefore preferred I wonder if this part is worth it. There might be cases in which a glitch free switch is required, but without being able to enforce a glitch free switch we can't rely on it. Also this makes the result depend on the current PLL settings, so the result is no longer reproducible. I.e. switching from a fari away frequency to the desired frequency might yield in different settings than switching from a nearby frequency to the desired frequency. Finally I think the glitch free switch doesn't work currently, because the PLL is fully disabled and re-enabled unconditionally in clk_fracn_gppll_set_rate(). That said, glitch free switching would be great to have sometimes. > - As a last resort the best settings are calculated dynamically > > Implementation is inspired by commit b09c68dc57c9d ("clk: imx: pll14xx: > Support dynamic rates") > > Signed-off-by: Alexander Stein > --- ... > + if (pll->flags & CLK_FRACN_GPPLL_FRACN) { > + if (!dist) { > + /* Disable fractional part upon exact match */ > + mfd = 1; > + mfn = 0; > + } else { > + mfd = 100; > + mfd = clamp(mfd, PLL_MFD_MIN, PLL_MFN_MAX); With mfd = 100 this clamp looks like a no-op. Do we need this? Sascha -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |