linux-kernel - Re: [RFC v2 3/5] arm64: dts: imx8mq: Combine PCIE power domains

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Date:   Fri, 08 Feb 2019 10:45:17 +0100
From:   Lucas Stach <l.stach@...gutronix.de>
To:     Andrey Smirnov <andrew.smirnov@...il.com>
Cc:     Shawn Guo <shawnguo@...nel.org>,
        Fabio Estevam <fabio.estevam@....com>,
        Chris Healy <cphealy@...il.com>,
        Leonard Crestez <leonard.crestez@....com>,
        "A.s. Dong" <aisheng.dong@....com>,
        Richard Zhu <hongxing.zhu@....com>, linux-imx@....com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC v2 3/5] arm64: dts: imx8mq: Combine PCIE power domains

Am Donnerstag, den 07.02.2019, 16:29 -0800 schrieb Andrey Smirnov:
> According to NXP's FAE feedback and a comment in ATF firmware, PCIE1
> and PCIE2 power domains can't really be used independently. Due to
> shared reset line both power domains have to be turned on at the same
> time. Account for that quirk by combining PCIE power domains into a
> single 'pgc_pcie' power domain.
> 
> Signed-off-by: Andrey Smirnov <andrew.smirnov@...il.com>
> Cc: Shawn Guo <shawnguo@...nel.org>
> Cc: Fabio Estevam <fabio.estevam@....com>
> Cc: Chris Healy <cphealy@...il.com>
> Cc: Lucas Stach <l.stach@...gutronix.de>
> Cc: Leonard Crestez <leonard.crestez@....com>
> Cc: "A.s. Dong" <aisheng.dong@....com>
> Cc: Richard Zhu <hongxing.zhu@....com>
> Cc: linux-imx@....com
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: linux-kernel@...r.kernel.org

Nit below, otherwise:

Reviewed-by: Lucas Stach <l.stach@...gutronix.de>

> ---
>  arch/arm64/boot/dts/freescale/imx8mq.dtsi | 21 ++++++++++++++++++++-
>  1 file changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/boot/dts/freescale/imx8mq.dtsi b/arch/arm64/boot/dts/freescale/imx8mq.dtsi
> index 50436bd393ed..89babc531380 100644
> --- a/arch/arm64/boot/dts/freescale/imx8mq.dtsi
> +++ b/arch/arm64/boot/dts/freescale/imx8mq.dtsi
> @@ -273,9 +273,28 @@
>  						reg = <IMX8M_POWER_DOMAIN_MIPI>;
>  					};
>  
> -					pgc_pcie1: power-domain@1 {
> +					/*
> +					 * As per comment in ATF source code:
> +					 *
> +					 * PCIE1 and PCIE2 share the
> +					 * same reset signal, if we
> +					 * power down PCIE2, PCIE1
> +					 * will be held in reset too.
> +					 *
> +					 * So instead of creating two
> +					 * separate power domains for
> +					 * PCIE1 and PCIE2. We create
> +					 * a link between 1 and 10 and

1 and 10 is not something that directly shows up in the DTS, so I think
it could be confusing to the reader. I would just state that as "link
between both" or something to that tune.

> +					 * use what was supposed to be
> +					 * domain 1 as a shared PCIE
> +					 * power domain powering both
> +					 * PCIE1 and PCIE2 at the same
> +					 * time
> +					 */
> +					pgc_pcie: power-domain@1 {
>  						#power-domain-cells = <0>;
>  						reg = <IMX8M_POWER_DOMAIN_PCIE1>;
> +						power-domains = <&pgc_pcie2>;
>  					};
>  
>  					pgc_otg1: power-domain@2 {