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

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Date:   Thu, 21 Jul 2022 14:54:54 +0800
From:   Xu Yilun <yilun.xu@...el.com>
To:     "Manne, Nava kishore" <nava.kishore.manne@....com>
Cc:     Nava kishore Manne <nava.manne@...inx.com>,
        "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

On Mon, Jul 18, 2022 at 06:46:32AM +0000, Manne, Nava kishore wrote:
> 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. 

If an external-fpga-config FPGA region needs to enable a power domain before
sub devices population, how could it config the DT? I assume in this
patch "power-domains" property is only used before & after
reconfiguration but external-fpga-config FPGA region may need no
reconfiguration.

> 
> > 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)

If a FPGA region needs 2 or more power domains for partial reconfiguration,
how could we find out and enable them all?

>From the 2 cases, I see as a generic driver, there may be need to enable
different power domains at different moments. And I'm afraid a simple
implementation of pm_runtime_get before reconfiguration may limit the
usage of "power-domains" property for of-fpga-region.

Thanks,
Yilun

>  
> > 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.