linux-kernel - Re: [PATCH v2 2/2] phy: rockchip: Add Samsung HDMI/eDP Combo PHY driver

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Message-ID: <61af7b121b23fe8ed06df5348692f862b9b125bf.camel@gmail.com>
Date: Mon, 12 Feb 2024 17:44:43 +0100
From: Luis de Arquer <ldearquer@...il.com>
To: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>, Rob Herring
 <robh+dt@...nel.org>, Krzysztof Kozlowski
 <krzysztof.kozlowski+dt@...aro.org>,  Conor Dooley <conor+dt@...nel.org>,
 Heiko Stuebner <heiko@...ech.de>, Johan Jonker <jbx6244@...il.com>, 
 Sebastian Reichel <sebastian.reichel@...labora.com>, Sascha Hauer
 <s.hauer@...gutronix.de>, Andy Yan <andy.yan@...k-chips.com>, Vinod Koul
 <vkoul@...nel.org>, Kishon Vijay Abraham I <kishon@...nel.org>, Philipp
 Zabel <p.zabel@...gutronix.de>, Algea Cao <algea.cao@...k-chips.com>
Cc: devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	linux-phy@...ts.infradead.org, kernel@...labora.com
Subject: Re: [PATCH v2 2/2] phy: rockchip: Add Samsung HDMI/eDP Combo PHY
 driver

Hi Cristian,

On Mon, 2024-02-05 at 13:24 +0200, Cristian Ciocaltea wrote:
> +
> +static bool hdptx_phy_clk_pll_calc(unsigned int data_rate,
> +				   struct ropll_config *cfg)
> +{
> +	const unsigned int fout = data_rate / 2, fref = 24000;
> +	unsigned long k = 0, lc, k_sub, lc_sub;
> +	unsigned int fvco, sdc;
> +	u32 mdiv, sdiv, n = 8;
> +
> +	for (sdiv = 16; sdiv >= 1; sdiv--) {
> +		if (sdiv % 2 && sdiv != 1)
> +			continue;
> +
> +		fvco = fout * sdiv;
> +
> +		if (fvco < 2000000 || fvco > 4000000)
> +			continue;
> +

What about adding a check to data_rate, maybe like

if (fout > 0x0FFFFFFF)
	return false;

or similar, before the for loop, to keep the multiplication safe?

Right now it would be redundant, given that data_rate was, at some
point, encoded in 28 bits within bus_width. But can prevent future pain,
especially after changing to phy_configure_opts_hdmi.

Luis