linux-kernel - Re: [PATCH v2 2/3] fpga: region: Add fpga-region 'power-domains' property

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Message-ID: <20220624162815.GA2142910@yilunxu-OptiPlex-7050>
Date:   Sat, 25 Jun 2022 00:28:15 +0800
From:   Xu Yilun <yilun.xu@...el.com>
To:     Nava kishore Manne <nava.manne@...inx.com>
Cc:     mdf@...nel.org, hao.wu@...el.com, trix@...hat.com,
        robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        michal.simek@...inx.com, linux-fpga@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, git@...inx.com,
        Rob Herring <robh@...nel.org>
Subject: Re: [PATCH v2 2/3] fpga: region: Add fpga-region 'power-domains'
 property

On Mon, May 23, 2022 at 07:15:16PM +0530, Nava kishore Manne wrote:
> Add fpga-region 'power-domains' property to allow to handle
> the FPGA/PL power domains.
> 
> Signed-off-by: Nava kishore Manne <nava.manne@...inx.com>
> Acked-by: Rob Herring <robh@...nel.org>
> ---
> Changes for v2:
>               - Updated power-domains description.
> 
>  .../devicetree/bindings/fpga/fpga-region.txt       | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/fpga/fpga-region.txt b/Documentation/devicetree/bindings/fpga/fpga-region.txt
> index 7d3515264838..f299c3749505 100644
> --- a/Documentation/devicetree/bindings/fpga/fpga-region.txt
> +++ b/Documentation/devicetree/bindings/fpga/fpga-region.txt
> @@ -196,6 +196,20 @@ Optional properties:
>  - config-complete-timeout-us : The maximum time in microseconds time for the
>  	FPGA to go to operating mode after the region has been programmed.
>  - child nodes : devices in the FPGA after programming.
> +- power-domains : A phandle and power domain specifier pair to the power domain
> +	which is responsible for turning on/off the power to the FPGA/PL region.

Could you help explain what is PL?

> +Example:
> +	fpga_full: fpga-full {
> +                compatible = "fpga-region";
> +                fpga-mgr = <&zynqmp_pcap>;
> +                #address-cells = <2>;
> +                #size-cells = <2>;
> +                ranges;
> +                power-domains = <&zynqmp_firmware PL_PD>;
> +        };
> +
> +	The PL_PD power domain will be turned on before loading the bitstream
> +and turned off while removing/unloading the bitstream using overlays.

I think the single power-domain may not cover some use cases that
of-fpga-region driver supports. It is possible there are already
devices in fpga-region for static OF tree, or an overlay with no
'firmware-name' but 'external-fpga-config'. In these cases power domains
may still be needed, is it?

Another case is the fpga-region may need multiple power domains?

Since the of-fpga-region driver is a generic fpga-region driver, we may
investigate more for a compatible power-domain solution.

Thanks,
Yilun

>  
>  In the example below, when an overlay is applied targeting fpga-region0,
>  fpga_mgr is used to program the FPGA.  Two bridges are controlled during
> -- 
> 2.25.1