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

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Message-ID: <DM6PR12MB39937A19AE147CD9105C8D52CD8C9@DM6PR12MB3993.namprd12.prod.outlook.com>
Date:   Mon, 18 Jul 2022 06:46:32 +0000
From:   "Manne, Nava kishore" <nava.kishore.manne@....com>
To:     Xu Yilun <yilun.xu@...el.com>,
        Nava kishore Manne <nava.manne@...inx.com>
CC:     "mdf@...nel.org" <mdf@...nel.org>,
        "hao.wu@...el.com" <hao.wu@...el.com>,
        "trix@...hat.com" <trix@...hat.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "michal.simek@...inx.com" <michal.simek@...inx.com>,
        "linux-fpga@...r.kernel.org" <linux-fpga@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "git@...inx.com" <git@...inx.com>, Rob Herring <robh@...nel.org>
Subject: RE: [PATCH v2 2/3] fpga: region: Add fpga-region 'power-domains'
 property

Hi Yilun,

	Please find my response inline.

> -----Original Message-----
> From: Xu Yilun <yilun.xu@...el.com>
> Sent: Friday, June 24, 2022 9:58 PM
> 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
> 
> CAUTION: This message has originated from an External Source. Please use
> proper judgment and caution when opening attachments, clicking links, or
> responding to this email.
> 
> 
> 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.

I am not sure which use case you are talking about. Can you please point me the exact use case here?
  
> 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?
>

It's an optional property user can decide whether he needs this support or not for 'external-fpga-config
Use case. 

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

In our use case full region and relevant partial regions have different power domains and
this patch is capable of handle different power domain regions (full and partial regions)
 
> Since the of-fpga-region driver is a generic fpga-region driver, we may
> investigate more for a compatible power-domain solution.
> 

Please share your thoughts here we will try to align with it.

Regards,
Navakishore.