linux-kernel - Re: [PATCH 2/6] drm: bridge: samsung-dsim: Fix PMS Calculator on imx8m[mnp]

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Date:   Mon, 17 Apr 2023 00:07:16 +0200
From:   Marek Vasut <marex@...x.de>
To:     Adam Ford <aford173@...il.com>, dri-devel@...ts.freedesktop.org
Cc:     m.szyprowski@...sung.com, aford@...conembedded.com,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Inki Dae <inki.dae@...sung.com>,
        Jagan Teki <jagan@...rulasolutions.com>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Robert Foss <rfoss@...nel.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Frieder Schrempf <frieder.schrempf@...tron.de>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/6] drm: bridge: samsung-dsim: Fix PMS Calculator on
 imx8m[mnp]

On 4/15/23 12:40, Adam Ford wrote:
> According to Table 13-45 of the i.MX8M Mini Reference Manual, the min
> and max values for M and  the frequency range for the VCO_out
> calculator were incorrect.  This also appears to be the case for the
> imx8mn and imx8mp.
> 
> To fix this, make new variables to hold the min and max values of m
> and the minimum value of VCO_out, and update the PMS calculator to
> use these new variables instead of using hard-coded values to keep
> the backwards compatibility with other parts using this driver.

[...]

>   static const struct samsung_dsim_driver_data imx8mm_dsi_driver_data = {
> @@ -470,6 +485,9 @@ static const struct samsung_dsim_driver_data imx8mm_dsi_driver_data = {
>   	 */
>   	.pll_p_offset = 14,
>   	.reg_values = imx8mm_dsim_reg_values,
> +	.m_min = 64,
> +	.m_max = 1023,
> +	.vco_min = 1050,

You might want to call this 'min_freq' since there is a 'max_freq' which 
seems to indicate what VCO max frequency is.

Note that the same datasheet contains the following information:
"
MIPI_DPHY_M_PLLPMS field descriptions

12–4 PMS_M
Specifies the PLL PMS value for the M divider
NOTE: The programmable divider range should be within 25 to 125 to 
ensure PLL stability.
NOTE: The M and P divider values should be considered together to ensure 
VCO ouput frequency
(VCO_out) range is between 350 MHz to 750 MHz.
Please refer to the topic DPHY PLL for more information.
"